Download Legend Ectoderm – covering cells, sensory and nerve cells, cells

Legend
Ectoderm – covering cells, sensory and nerve cells, cells that cover the front and back
of the digestive system
Endoderm – cells that cover most of the digestive system, glands and digestive
organs.
Mesoderm – all other tissues, muscles and reproductive organs/cells. Its initial
function is the sex cavity.
Fuckies = reproduction.
Kingdom Protista
Phylum Protozoa
Exists.
Kingdom Animalia (Multicellular)
Subkingdom Parazoa
Phylum Porifera (Sea Sponges)
Come in a variety of shapes and sizes, from millimeters to meters. Most are marine,
but freshwater exist as well. The flow of water determines the hardness of the
organism. They lack a nerve system or definite sensory cells.
Choanocytes – ciliated cells of symbiontic origin that filter food particles.
Pinacocytes – A form of epithelial cells.
Fuckies is asexual by budding and fragmentation, most species are dioecious.
Structural types:
 Asconoid – Simplest and least effective.
 Syconoid  Leukonoid – Most efficient, these grow to become the largest.
Sponges are an evolutionary dead end. Predatory species have been described.
Subkingdom (Eu)Metazoa (True Tissues)
Superphylum Coelenterata (diplobalastic)
Phylum Cnidaria (Primary radial symmetry)
All are aquatic, some are marine, Gastrovascular feeding system
Cell types
Epithelio-muscular cell – serves for motion and protection, not a muscle cell, contains
contractile fiber. These are the only cells not replenished by interstitial cells. Nerve
and sensory cells form an array between them.
Cnidocyte (cnidoblast) – serves as a weapon, contains an organelle called a
nematocyst. The nematocyst (20 different types) is made of a sac containing a
corrosive liquid and a coiled barbed wire. The cnidocil is a sensitive hair outside
which triggers the explosive reaction and is primed by a chemical trigger secreted by
the prey. The discharge mechanism is osmotic pressure, which causes the discharge of
the barbed wire. Cnidocytes are concentrated on the tentacles and around the mouth.
Some cnidaria have array of nematocysts inside their digestive tract. These cells are
disposable and are replaced by differentiation of interstitial cells.
Interstitial cells
Sensory cell
Mesoglea – not actually a cell, but worth mentioning.
Nutritive-muscular cell – feeding cells that perform phagocytosis and perform
intracellular digestion.
Gland cells – secrete digestive enzymes for extracellular digestion.
Nerve cells – bipolar.
Class Hydrozoa (‫)הידרות‬
Most are marine and colonial, most have a benthic and a pelagic stage, some live in
freshwater and lack a pelagic stage, some are marine and lack a benthic stage.
Some polyps think they're acrobats and flip in a gay manner.
Medusae are small and have vellum, contain contractile fibers for swimming, not
actual muscles.
Digestion is both extracellular and intracellular.
Breathing is done via diffusion throughout the entire surface area of the body.
Sensory perception is based on sensory cells and a non-centralized nervous system.
Fuckies usually by two stages unless mentioned otherwise.
Genus Hydra
A solitary animal, lives in freshwater, has no pelagic stage, and performs symbiosis
with zoochlorellae.
Resting eggs - coated with a protective layer that allows them to survive harsh
conditions
Genus Obelia
Marine colonial organism in its (primary) polyp stage (sexual generation) that
reproduces asexually, has a medusoid (asexual generation) stage that reproduces
sexually. Obelia prefer darker conditions as to not compete with algae and to provide
better conditions for the planula.
Genus Milleporina (fire corals)
Excrete a hard calciform skeleton, have a medusoid stage (sexual) and a polyp stage
(asexual) where colonies are grown. Not actual corals (don’t belong to anthozoa).
Genus Physalia (Species Physalis)
An intermediate between a colony and a multicellular organism. One polyp inflates to
form the sail and the entire colony floats near the surface. The rest are either
gastrozoid or gonozoids.
Class Scyphozoa (‫אמיתיות‬/‫)מדוזות סוכך‬
Mostly marine, solitary, lack a vellum, the medusoid stage is the primary one. The
mesoglea is exceptionally thick and causes stability. They are usually large compared
to the Hydrozoan medusae.
Ring canals – allow contraction.
Radial canals – improves diffusion of oxygen and nutrients.
Rhopalium – contains a cluster of sensory cells (also found around the mouth), which
contain photoreceptors, chemoreceptors, mechanoreceptors and a statocyst (for
balance).
Manubrium – oral tentacles
The nervous system is effectively a net of nerves.
Gastral filaments line the entercoel, containing cnidocytes, and paralyze struggling
prey. These detach to open water especially when the organism is dying.
The life cycle is: zygote  ciliated planula larvaue that swims to the ground
scyphistoma  young strobila  strobila  ephyra  medusa.
Movement is achieved by rhythmic contraction of the umbrella (contains contractile
filaments at the edges). Higher water temperature generates faster movement.
Solid waste is removed through the mouth, liquids and gases (ammonia included) are
diffused outward.
Genus Rhopilema nomadica (‫)חוטית נודדת‬
Invaded the Red Sea from the Mediterranean, created giant populations.
Genus Cassiopeia andromeda
Lives in the shallow water of Eilat, starts as pelagic and becomes benthic (lays on its
umbrella). Its mouth closes up at an early stage and small holes for feeding open up.
Genus Rhizostoma pulmo
Colorful, bell shaped.
Class Anthozoa
The largest class of cnidarians, all are marine. Lack a medusoid stage, have the largest
polyp of all cnidarians, some are solitary, some colonial. Most are supported by both
an internal and external skeleton.
Subclass Hexacorallia (Zoantharia)
The gastrovascular cavity is divided into six sections, divided by septa. Septa can be
complete or partial (primary -complete, secondary and tertiary - incomplete), and are
useful for increasing the surface area of the gastrovascular tract. The pharynx is
covered in ectoderm as the body folds inwards to create the septa.
Order Actinaria (sea anemones)
Colorful, maintain symbiotic ties with plankton, fish and mollusks, usually on firm
ground (some can stay on soft).
Fuckies is both sexual and asexual. Asexual is done via tearing of the body. The
sperm is released into the water, enters the female and fertilization occurs in the
gastrovascular tract. Mostly dioecious and gonochroistic (separate sex organs).
Genus Radianthus (‫ )שושנתן‬and Amphiprion (‫)שושנון‬
Common in warm water, lives in symbiosis with amphiprion (Radianthus protects the
fish which is believed to herd prey to the anemone in return).
Genus Anemonia sulcata (‫)דונגית צורבת‬
Mediterranean, lives in shallow water, colored bright red. Does not contract. Lives on
small fish and such.
Genus Actinia equine (‫)שושנה אדומה‬
Mediterranean, very common, lives on rocks in shallow water, can live outside of
water. Colored deep red, can move by disconnecting its pedal disc, lives on plankton.
Order Scleractinia (stone corals)
Excrete calcium carbonate from the ectoderm to form a hard exoskeleton, all are
colonial reef builders, mostly in war clear and photic water.
The gastrovascular tract is joint amongst the entire colony.
Symbiosis with zooxanthellae where the polyp supplies nutrients and the algae
supplies energy through photosynthesis (explains the need for photic water). Subject
to coral bleaching due to increased pathogenic activity, which in turn is because of
rising ocean temperatures due to global warming.
Asexual fuckies is via tearing and growing nearby (doesn't start new colonies), sexual
fuckies consists of simultaneous release of gametes in synch with the lunar cycle.
Fertilization is external, forms a planula and continues like the anemones. Some are
monecious.
Genus Favia (‫)אלמוגן‬
Spherical colony of polyp, separated by cones. Important reef builders.
Genus Platygyra (‫)מוחן‬
Looks like a brain because of the structure of the colony.
Genus Fungia (‫)אלמוג הפטריה‬
Single polyp, benthic, is not attached to the ocean floor, the young ones are mobile, if
slowly.
Subclass Octocorallia (Alcyonaria)
Eight-based symmetry, have eight tentacles, all are colonial and have a joint
gastrovascular tract, the polyp are connected by gastrodermal tubes called solenia.
The endoskeleton is inside the coenchyme, a soft tissue formed within the mesoglea,
made of a matrix of sclerites made of calcium carbonate or chitin. These can
intertwine and create a rock-hard skeleton.
Genus Gorgonacea (‫)גורגונאים‬
Colonies of soft corals containing an endoskeleton, live in cold and deep water.
Family Pennatulidae (‫)נוצות ים‬
Found in the Mediterranean, have a endoskeleton made of chitin. Live polyps bud of
the arms.
Phylum Ctenophora
Exists.
Phylum Platyhelminthes (bilateral symmetry, triploblastic,
acoelomata, protostomia, spiral cleavage, schizocoelic, determinate cleavage,
cephalization, advanced nervous system, advanced muscular system)
Development of the mesoderm
The mesoderm allowed the formation of muscles, which allowed for greater mobility,
which required cephalization and a more complex nervous system. The development
of muscles caused an increase in body mass, which led to the formation of bodily
systems: vascular, respiratory, excretory and skeletal. Cephalization gave the body
directions, and is a staple of bilateral symmetry.
Class Turbellaria (free living ciliates)
First appeared during the Cambrian. Live in marine, freshwater or moist terrestrial
environments. Contain 3,000 species.
The mesoderm becomes a soft tissue called parenchyme (due to its mesodermal
origin, also called a mesenchyme), which contains muscle and internal organs. It also
serves as an internal support which the muscles contract against since there is no
skeleton.
Rhabdite – rod like structures (created in cells also called rhabdites) which are formed
in the mesenchyme or the ectoderm, excreted and dissolve, presumably for defense.
The head contains:
Auricles – concentrations of chemoreceptors.
Ocelli – A pair of simple eyes, connected to an optic nerve. They cannot form an
image, but can detect different levels of light and its direction. The cornea is made of
transparent ectoderm. Ectoderm in other areas contains a dark pigment to prevent
light from entering from all directions.
Lateral cord?
Dorsal cord?
Digestion
The digestive system is gastrovascular, beginning with a mouth attached to the
pharynx which leads to leads to the digestive system. The type of digestive system is
used for taxonomic division into orders (see below).
Motion
Mucus secretion gland - Movement is achieved either by cilia grown on the ventral
side which move along an excreted layer of mucus, or by complex coordination of
muscles in a pulling-pushing motion.
Sensory system
Nerve strands and ganglions – Nerve cells are arranged in fibrous and strip-like
structures. Where these strips meet or diverge, clusters of nerve cells called ganglions
form. The nerve system includes a ring of nerve cells around the head and divergence
into strips along the body. A more advanced structure is the pair of cerebral ganglions
out of which two primary strands extend along the body and diverge along the way
(forms a ladder structure).
Types of sensory cells:
Mechanoreceptors – highly concentrated on the ventral side.
Rhotactic cells – sense the water current.
Chemoreceptors – highly concentrated on the head.
Photoreceptors – for light (cuz that's what they do)
Breathing
Breathing is done via diffusion throughout the entire surface area of the body.
Excretion
Protonephridia (a.k.a flame cells, though it looks like a penis with three testicles) –
Consist of a dual system of tubes along the body with openings for excretion and
drainage. These tubes branch out into smaller tubes, the ends of which contain flame
cells (the protonephridia itself) which are blind (have no second opening). Matter
from the mesenchyme diffuses into the flame cells.
Flame cell – The cavity contains flagella that beats and generates pressure that moves
waste and metabolites along the tubules and then tubes towards nephridiopores,
excretory openings. During this movement, nutrients and water are reabsorbed. This
system maintains osmoregulation and ionoregulation.
Excretion of solids is done via the mouth.
Fuckies
Fuckies is achieved asexually via fragmentation or budding of new individuals. This
form of fuckies is based on the organism's regenerative ability through cells in the
mesenchyme. It can also feed on its own tissue and reduce it weight by 2/3.
Most turbellarians are dioecious, so two random worms, strangers to each other, end
up having sex which results in double impregnation (twice the number of unwanted
children and evil stepparents). Each worm has a penis and a sexual atrium.
Eggs are laid one at a time or in groups, and are coated with a protective layer that
allows them to survive harsh conditions (resting eggs).
Order Rhabdocoela (‫)חסרי סעיפים‬
Exists.
Order Polycladida (‫סעיפיים‬-‫)רב‬
Exists.
Order Tricaldida (‫סעיפיים‬-‫)תלת‬
Genus Dugesia (Planria!!)
Dorsoventrally flattened (like a pita), the pharynx is detachable and is located in the
posterior end, ventral side. Planrians have developed latitudinal, longitudinal, oblique
and circular muscles.
Parasitic classes
Adaptations to parasitism include: decay of digestive system, development of
complex reproductive cycle (possibly several intermediate hosts), development of
methods of attachment to the host.
Class Trematoda
Genus Schistosoma mansoni (‫)בילהרציה‬
Class Cestoda (‫)שרשורים‬
Genus Echinococcus (‫)שרשור הכלב‬
Genus Taenia saginata (‫)שרשור הבקר‬
Phylum Nematoda (pseudocoelomata)
Exists.
Phylum Annelida (coelomata, segmentation, circulatory system, some
have secondary radial symmetry)
Segmentation
Segmentation consists of a metameric structure, either homomeric or heteromeric.
Segmentation occurs via development of a series of consecutive coelom sacs along
the digestive tract. Partitions between the right and left side of the body occur on the
dorsal and ventral sides and are called mesentry. Between adjacent coelom sacs are
septum that divide the sacs. Segmentation serves as the beginning of the evolution of
bodily divisions.
Each segment contains:
 latitudinal, longitudinal and oblique muscles for advanced independent
movement.
 a coelom which serves as a genital atrium, vascular system, hydrostatic
skeleton and protective perivisceral cavity
 excretory organs – nephridia occur in pair in each segment.
 nervous system, ganglions - The primary nerves strands run along the length
of the body, but are only ventral. Every segment contains a pair of ganglions.
Vascular systems
The coelom contains two primary blood vessels (dorsal and ventral) that grow along
the entire body and pass through all the segments. The blood is pumped by five pairs
of accessory hearts, thick aortic arches which surround the digestive systems. The
primary vessels branch off towards the segment wall and organs in every segment.
The blood vessels serve as an additional vascular system to the coelom and both are
closed systems – no excretion through the gastric system.
Peritoneum (‫ – )קרום צפק‬epithelial cells of mesodermal origin, that surrounds the
coelom sacs.
Sensory system
Some polychaetes have a ladder-like nervous systems, others and most annelids show
a merging of the two nerve strands and cerebral ganglia.
The two large cerebral ganglia lie above the pharynx, a smaller subpharyngeal
ganglion lies just beneath and each segment has a pair of ganglia.
Large ventral nerve strands run along the annelid's body, branching out to the
ectoderm where they connect to sensory cells: mechano-, chemo- and photoreceptors.
Worms have ocelli.
Breathing
Breathing is done via diffusion through the entire surface of the body, the terrestrial
forms are moist, the aquatic forms have parapodia that serve as gills.
Digestion
Digestive system is as follows: food enters through the pharynx  esophagus (‫)ושט‬
 crop (‫ )זפק‬ gizzard (‫ )קיבה טוחנת‬ intestine (‫ )מעי‬ rectum (‫ )מעי גס‬ anus.
The entire system is pharynx to intestine and covered in ectoderm.
Food is stored in the crop, where it is subjected to digestive enzymes from the saliva,
the gizzard mechanically degrades the food and releases enzymes (acidic
environment), the intestine repeats the process in an alkaline environment and begins
the absorption of nutrients, the rectum reabsorbs water and feces are excreted through
the anus.
Excretion
Nephridia (a.k.a. metanephridia) serve as an excretory system, one pair in each
segment, where each is a ciliated funnel (nephrostome) connected to a long tube that
twists in order to increase time allowed for salts and water to be reabsorbed (the area
is surrounded by blood vessels), with an exit on the other end (nephridiopore). The
nephridiopore exists in one segment, while the tube and nephridiopore are in the next.
The coelom fluid drains here.
Fuckies
Different for each class, see below.
Class Polychaeta (‫זיפיות‬-‫)רב‬
Contain over 10,000 species, mostly marine, 5-10 cm in size, live in crevices. Some
are benthic, others free living (errantia).
Homomeric, have eyes and palps (‫)בחנינים‬, have cuticular jaws (which is deteachable,
as is the pharnx). All have parapodia –muscular extensions of the body wall, serve to
aid swimming and as a primitive gill. This requires circulation into the parapodia.
Benthic types have secondary radial symmetry due to the expansion of a circular array
of feathery arms extending out from near the palps that are used mostly for breathing
and filter feeding. The rest of the body is encased in a hard excreted tube, sometimes
containing calciumcarbonate, parapodia are retracted.
Others dig themselves into the ground and use their frontmost paradpodia as food
collecting arms, the others serve as gills. These species have the smallest parapodia.
Fuckies is achieved via fragmentation, meaning a new head segments is grown which
grows a few segments and then cuts off the original organism (autotomy). Polychaeta
are more primitive and hence have greater regenerative abilities. These abilities don’t
exist in polychaetes and hirudineans.
Polychaetes are dioecious, meaning internal fertilization isn't necessary. The gonads
are no more than a bulge of the peritoneum, and reside in every segment. The gametes
are stored within the sex atriumas. Sex cells are released through the nephridiopores,
sex tubes or breakage of the segment wall. Some species grow gamete producing
segments which break off and discharge the cells.
The polychaetes developmental cycle is such that the larvae (trochophores) do not
externally resemble the adults (metabolous).
Genus Eunice viridis (‫)פאלולו‬
In Fiji and Samoa, these marine worms synchronically appear due to the lunar cycle.
Freaky people on the island eat these worms. Ewwwwww.
Class Oligochaeta (‫זיפיות‬-‫)דל‬
Contain 3,500 species, live in freshwater and moist earth. These worms specialized in
digging and their parapodia have degenerated.
These species evolved thicker bristles called seta for movement, which are attached to
their oblique muscles. They are useful for digging into the ground and for holding on
to mates during fuckies.
This class is monoecious and mating individuals mutually fertilize each other. The
possess a thick band called clitellum (‫ )חגורת התבגרות‬the excretes mucus that allows
the transfer of sex cells.
The male reproductive system contains two pairs of testes, three pairs of vesiculae
seminalis (‫ )שלפוחיות זרע‬and a pair of semen tubes.
The female reproductive system contains a pair of ovaries, a pair of egg sacs, pair of
egg tubes and two receptacula seminis (‫)שקי זרע‬
During fuckies, both individuals attach to each other and through the secretion of
mucus transfer sperm from the vesiculae seminalis to the receptacula seminis. Both
individuals then dig into the ground and lay eggs.
The larvae appear as smaller versions of the adults. (‫)התפתחות ישירה‬
Class Hirudinea (‫)עלוקות‬
Contain 500 species, found mostly in freshwater and in moist earth, live as both
ectoparasites and predators. They have suckers around their mouth and on their rear
end. Named after the anti-coagulant they excrete into the bite-wound: hirudinin.
Some of the segments are lost in this class via fusion, though externally their
appearance remains like the other classes'.
Their digestive system is more massive and branched to maintain all the blood they
consume.
They possess both ovaries and testes.
Mandatory reading on leeches.
At the center of the head are three jaws, each containing 100 tiny cuticular teeth. The
bite sign looks like the Mercedes logo.
The larvae appear as smaller versions of the adults. (‫)התפתחות ישירה‬
Phylum Arthropoda ()
75% of the species in the world.
Produce food and are quite tasty too.
The reasons for the tremendous success of the arthropod design are:
1. An external skeleton, both light and durable – the skeleton serves as a durable
structure for muscles, allowed the development of massive muscles. Its
relative lightness allows for nimble efficient movement, including jumping
and flying. It also served as mechanical defense and protection for loss of
water. Molting started off as a handicap (since the body cannot grow when
encased in a skelton), but ended up as an ecological advantage, as there is no
competition between younglings and adults.
2. Bodily divisions (heteromeric) and focus of function – this division allows
each part of the body to serve a different function.
3. Jointed limbs adapted to different functions – allows for advanced motion, as
well as adaptation to serve different functions (climbing, jumping, flying,
digging, swimming etc.)
The exoskeleton
1. Durability
It allows for greater strength based on much less volume. Pressure due to bending is
much smaller as opposed to an endoskeleton.
Is made of cuticular matter which is excreted by the epidermis, it contains proteins,
fats, chitin and sometimes carbonate.
The cuticle is made of two primary layers:
 Epicuticle – external layer.
 Procuticle – internal later, comprised in turn of two layers:
o Exocuticle
o Endocuticle
Small canals run through the cuticle from the epidermis beneath, through which the
different cuticular substances are excreted.
In addition, excretory canals also run through the cuticle to excrete substances such as
pheromones.
The cuticle refracts light and can cause iridescence, color of physical (as opposed to
chemical) origin.
Due to segmentation, each segment's cuticle forms a plate. Plates are named based on
their location:
 Tergite – dorsal plates
 Pleurite – side plates
 Sternite – ventral plates
A thin, flexible cuticle connects the plates. In some cases, the sternite and tergite fuse
together (decapods exhibit this, as well as calcification of the exoskeleton.)
2. Attachment for muscles
An inward fold called the apodem serves as an attachment site for muscles, which
appear in each segment as in annelids. The muscles attach at this one site, as opposed
to an endoskeleton, in which the muscles cover the bone.
3. Changes in form and function
 Holometabolous (‫ – )גלגול מלא‬There is a chrysalis stage, during which the
larvae becomes and adult.
 Hemimetabolous (‫ )גלגול חסר‬- There is no chrysalis stage, the larvae gradually
grows into an adult.
The development of the exoskeleton required the disappearance of the hydrostatic
skeleton, and the division of the body required the fusing of segments and the
disappearance of the septa, causing the coelom to fuse. There became no use for a
complex circulatory system, and the blood and coelom liquid mixed to form
haemolymph. The joint blood-coelom system is called the haemocoelom.
Jointed limbs
Jointed limbs are an extrusion with its own skeleton, jointed muscles and connected to
the body by a joint. The origin is probably a muscular extrusion. There is no clear
evolutionary connection between parapodia and jointed legs.
Types
Defense and food handling (crab pincer)
Motion (insect leg)
Swimming (in some insects)
Sensory (antennae)
Mandible
Reproductive organ (in crabs)
Bodily divisions
Head + body - millipede
Cephalothorax + abdomen - shrimp
Head + thorax + abdomen - ant
This allowed centralizing function in one area, such as an excretory system in insects
located around the abdomen, and excretory glands in crustaceans located in the head.
The reproductive system is centralized in the abdomen.
Nerve and sensory system
Arthropods display a variety of nervous systems, ranging from primitive to modern:
 Primitive ladder-like system (crabs)
 A thread lined with ganglia (annelids)
 Cephalic, thoracic and abdominal ganglia (insects)
 Cephalic and abdominothoracic ganglia (insects)
 Abdominocephalothoracic ganglia (chelicerates)
More advanced insects developed three brains – protocerebrum, deuterocerebrum and
tritocerebrum. This allows for greater sensory perception and social communication.
Sensation is generated by extracting a hair (sensillae or seta) through the cuticle, and
the bending of the hair causes a change in the voltage in the hair socket, transferred
via neuron.
Chemoreception occurs by extending hollow hairs through the cuticle through which
signaling molecules can enter.
Sight
Larvae have lateral ocelli which become centralized in the adult, which also develops
compound eyes.
The ocelli concentrate light through one lens and absorb it through several retinulae
which are surround by pigmented cells to prevent light from entering from all
directions. Ocelli can only discern levels of light.
The compound eye is distinct to arthropods, comprised of individual structures called
omatidia. Each one is independent, like its own ocellus. The overall picture is mosaic.
Omatidia are built much like ocelli, but the retinuale surround a central rod-like
structure called a rhabdom that contains rhodopsin, which degrades and reforms. The
photons pass through the rhabdom. Each omatidia is surrounded by pigmented cells to
prevent a photon activating one cell from activating others (which would cause
amplification of light).
Breathing
Aquatic arthropods breathe through gills. The gills are stored in a gill chamber that
can store water for temporary adventures out onto land. Gas exchange is haemolymph
mediated.
Terrestrial arthropods have book lungs with a large surface area. Book lungs are
intrusions of the body wall, creating thin partitions surrounded by haemolymph. Air
flows in and passes through the partitions where gas exchange with the haemolymph
occurs.
The most terrestrial forms developed trachea, breathing tubes that originate from the
body wall that branch off and reach the target organ. This allows for one-way
breathing, the air enters the body through small openings that line the body called
spiracles. Gas exchange is done without haemolymph mediation.
Classification by antennae:
One pair – Trilobita and Uniramia
Two pairs - Crustacea
None – Chelicerata
Classification by legs:
Uniramous – Uniramia, Chelicerata
Biramous – Crustacea, Chelicerata
Classification by breathing system:
Book lungs – Checlicerata
Trachea – Uniramia
Gills - Crustacea
Subphylum Trilobita (‫אונתיים‬-‫)תלת‬
Extinct. Marine group consisting of 4000 species. Their body was divided into three
segments: cephalon, thorax and pygidium. The head-shield contains three lobes: one
front, two side. A skin flap growing from the head backwards covered the body, but
segmentation can still be seen. They lacked mandibles.
Subphylum Uniramia (‫)חד סעיפיים‬
Contains two forms of segmentation: cephalon-thorax-abdomen and cephalon-thorax.
In both cases, only the thorax has legs (in the former configuration the abdomen may
contain leg remnants.)
The head appendages include a pair of pre-oral antennae and three pairs of jaws:
mandibles, maxillae (fused in insects to form the labrium) and hypopharynx. The last
two have palps.
Excretion
The decidedly terrestrial forms have malpighian, blind tubes which drains into the
rectum, which prevents water loss.
Subphylum Checlicerata (‫)עכבישניים‬
Their body is segmented into two parts: cephalothorax and abdomen. Lack antennae.
Excretion
Via a series of coxal glands (originally part of the coelom), a long tube called a
labyrinth connects them to a bladder, excretion via the hip of the rear legs.
Class Merostomata (‫)גוף חרב‬
Class Pycnogonida (‫)עכבישי ים‬
Class Arachnida (‫)עכבישים‬
Subphylum Crustacea (‫)סרטנים‬
Two pairs of antennae.
The most diverse of arthropods (not the richest, but contains some 75,000 species).
Common in marine and freshwater environments, and their significance to aquatic
ecology is similar to insects' in terrestrial ecology.
The crustacean body shows a clear evolutionary trend of fusing segments, reduction
of the number of appendages and their specialization. This is obvious in the transition
from brachipoda to malacostraca.
Crustaceans have a flap of skin that folds backwards over their body (like the
trilobites) that fuses with the cuticle to form a strong carapace, usually reinforced by
carbonate. In some, the carapace forms the gill chamber which allows some decapods
to venture out to land.
Crustaceans have five pairs of head appendages:
Two pairs of pre-oral diantenata, a short first pair (antennule) and a second longer
pair (antenna).
Three post-oral appendages – anterior gnathobasic mandibles, a maxillule pair and a
maxilla pair.
Excretion
Via a pair of excretory glands in the head.
Class Malacostraca (‫)סטנים עילאיים‬
Class Brachipoda (‫)סרטנים ירודים‬
Phylum Echinodermata (Deuterostomia, enterocoelic, secondary
radial symmetry, non-segmented)
Marine animals, 6,500 recent, 13,000 fossilized. Have an endoskeleton (residing
under the epidermis made of small calcerous plates) that surrounds the body with
calciform protrusions that resemble spikes. The secondary radial symmetry is
pentamerous (five-based), with the larvae being bilaterally symmetrical.
Unlike the cnidarians, the oral side is also the basal side.
Mobility
Mobility is achieved primarily by the ambulacral system of "water legs". An opening
called the madreporite allows water to enter the stone canal which is held in place by
skeletal protrusions. The stone canal leads to the circular ring canal which breaks of
into water canals in each arm. Branching from the water canals in the hundreds are
ampullae, small sacs that taper downward to form the legs themselves. The sac ends
compress and become the legs become rigid (unidirectional valves prevent the flow of
water backwards). The legs contract with the contraction of a longitudinal muscle.
Nervous and sensory system
A nerve ring form in the center, send radial nerves off into the arms which branch out
under the epidermis. There is no central nervous system of formation of ganglia.
Ocelli are spread out over the body and the ambulacral system is partially sensory.
Feeding
Some have a detachable pharynx and expel digestive fluids onto their prey
(Astroidea). A central stomach branches off as a pyloric tube into each arm, each
containing its own pyloric caecum.
In sea urchins, a chewing mechanism called Aristotle's Lantern contains five united
teeth made of calcium carbonate with a fleshy protrusion within.
The ambulacral legs can be used to attach to and pry open clams.
Small pincers called pedicellaria remove waste, plankton and parasites.
Breathing and excretion
Diffusional. Small flexible protrusions serve as gills.
Fuckies
Asexual – based on regenerative ability.
Sexual – gonads extend into each arm and open up into the external environment to
discharge gametes. Fertilization is usually exterior. The zygote develops in a larva
which undergoes metabolous development.
Similarities between echinodermata and chordates
Radial cleavage, non-determinate development, both are deuterostomes, both are
coelomata, but echinoderms are enterocoelomates while chordates are
schizlocoelomates.
Class Astroidea (‫)כוכבי ים‬
Class Ophiuroidea (‫)נחשוני ים‬
Class Echinoidea (‫)קיפודי ים‬
Class Holothuroidea (‫)מלפפוני ים‬
Class Crinoidea (‫)חבצלות ים‬
Phylum Hemichordata
Sister phylum of both echinodermata and chordata. Worm-like marine animals, have
the pharyngeal gill slits typical of chordates as well as a post-anal tail, have a dorsal
nerve cluster which does not form into the typical chordate spinal cord, no notochord
but a mass of cells forms a firm structure in the anterior.
The larva is called a dipleurula and carries a cilia belt around its mouth and underside,
as opposed to the trochophore (annelids and platyhelminthes) which has one around
the body under the mouth.
Their mesoderm forms in the enterocoelic fashion.
Phylum Chordata (deuterostomia, bilateral symmetry)
The primary features of chordates are:
1. Notochord – made of vertebrae in most, the limbs connect to it, as fins in
aquatic forms and limbs in terrestrial forms.
2. Dorsal nerve cord
3. Post-anal tail
4. Pharyngeal gill slits
5. Ventral heart (where present)
6. Arterial arches around the gills.
7. Segmentation of muscles around the notochord
8. Developed coelom
9. Closed vascular system
Subphylum Protochordata
Class Urochordata (Tunicata)
2,000 species
Class Cephalochordata (acraniata)
25 species
Lancelets (Amphioxus, ‫)איזמלון‬
Additional features:
1. Lacks a skull or brain
2. Simple digestive tract, intracellular digestion.
3. Hepatic diverticulum
4. Single layer of epithelial cells
5. No heart, but arterial arches present
6. Diffusional breathing, the blood has no pigment.
The lancelet has three exocrine glands which are thought to be precursors to
vertebrate endocrine glands:
1. The endostyle, which is thought to become the vertebrate thyroid gland (an
experiment was done with iodine, which concentrates in the thyroid, and was
seen to concentrate in the endostyle).
2. Hatscheks pit, which is thought to become the adenohypophysis.
3. Kolliker's pit, which is thought to become the pineal gland.
Has flame cells much like the flat worms, functionally similar to the vertebrate
pronephros.
The pharyngeal gill slits are used for filter feeding, not breathing.
Subphylum Vertebrata
Primary features
Notochord – made of vertebrae in most, the limbs connect to it, as fins in aquatic
forms and limbs in terrestrial forms.
Craniata – have a skull and skeletal structure in general. The cartilage forming it
originates in the neural crest.
5 brains – exist in all except cyclostomata, reside in the anterior part of the nerve
cord.
Nerves - 10 or 12 pairs of nerves in the head, segmental nerves.
Bodily division – head, abdominothorax and tail. Terrestrials have a neck.
Skin – Multilayered epidermis and dermis.
Heart – located ventrally, 2-4 chambered with arterial arches that connect it to the
dorsal arteries.
Digestive system – Complex, with many secretion glands as well as two large glands
(liver and pancreas).
Developed coelom – contains a thoracic (pericard) and abdominal cavity
(peritoneum).
Excretion – developed organs that excrete outside the body.
Endocrine – Many glands.
Dioecious – the reproductive system has ducts leading outwards.
Class Cyclostomata (craniata, agnatha)
The sucker is called petromyzon, the larva is called ammocoetes.
Muscular pharynx for propulsion of water through the gills.
Has a primitive inner ear.
The life cycle begins in the ground in streams, metamorphosis over several years,
emergence and migration towards lakes where the parasitize fish.
The larva have a pronephros, adults have a mesonephros. Have a functional thyroid
gland.
Higher vertebrates
Embryogenesis
Gametogenesis
Summarized by meiosis.
Fertilization
The egg consists of the nucleus, a polar body which ejects after fertilization, yolk, an
inner plasma membrane and external vitelline membrane and cortical granules. A jelly
coat surrounds the egg.
An incoming sperm releases acrosomal enzymes which digest the jelly coat, proteins
on the sperm head bind to a receptor located in the egg, the cortical granules discharge
and form a fertilization membrane (which sets the size of the blastula) and an electric
discharge prevents any other sperm cells from entering. The sperm and egg nuclei
fuse and the polar body is ejected. Cleavage begins.
Cleavage
The zygote rapidly divides, causing the entire cell mass to contain more cells whose
total weight never changes. The cells created by these divisions are called
blastomeres. The first three divisions are perpendicular to each other, two vertical,
one horizontal.
As the cells divide and move, they form a space in the middle (morula stage).
Cleavage can be one of two types: holoblastic or meroblastic. Eggs come in three
types, depending on the amount of yolk in them: isolecithal, merolecithal or
telolecithal.
 In lower vertebrates and mammals we see radial holoblastic cleavage of
isolecithal eggs.
 In amphibians there is radial holoblastic cleavage of mesolecithal eggs.
 In birds we see discoidal merblastic cleavage of telolecithal eggs, meaning
division occurs only at the animal pole where there is a lower yolk
concentration.
In meroblastic division, smaller cells are called micromers and larger cells are called
macromers.
When the egg reaches the blastula stage (after the morula's space closes up), a fate
map determines the fate of each type part of the embryo.
Gastrulation
In the vegetal pole (macromers), invagination occurs and the cells migrate inwards to
form the endoderm. This is because micromere division occurs faster and pushes the
heavier macromers inwards, and also because the macromers actively migrate inwards
(determined in advance by genetic programming).
Invagination continues until the endoderm touches the ectoderm from its internal side.
This contracts the blastocoel until it disappears, the gastrocoel (archenteron) forms.
The blastopore closes up and the future anus opens up nearby (deuterostomes).
Vertebrates are deuterostomes and hence enterocoelous. The gastrula "falls over",
elongates and starts exhibiting bilateral symmetry. The lower part is the endoderm,
the upper part is the mesoderm.
The difference between the archenteron and enteron is that a true enteron is
surrounded by gastroderm alone. The archenteron has a mesoderm roof.
Neuralation
A part of the ectoderm sinks in wards and folds around a central axis to form the
neural tube in which the spinal cord will form.
Organogenesis
The central part of the mesoderm roof because the notochord. The mesoderm on both
sides is called the lateral mesoderm. These break off and close up, forming cavities
within. These cavities are enterocoelic (originate in the archenteron). The mesoderm
with the cavity is called a somite. Segmentation occurs in vertebrates, so each
segment will have a pair of somites. This exists in echinodermata and chordates, but
not other invertebrates. The rear segments of amphioxus are schizocoelic in origin,
connecting the chordates with the invertebrates. Their coelom is schizocoelic.
In chordates somehow, each pair of somites actually forms a schizcoelic cavity, after
an enterocoelous one already exists. WTF?!
The schizocoel separates the splanchnopleura (touches the endoderm) from the
somatopleura (touches the ectoderm). The somites of both side join together later on
and form the abdominal cavity, but not in it's top part where they remain separate
(mesentry – like in annelids).
The splanchnopleura forms the smooth muscles of the intestines (only the interior is
endodermal) and the vascular tissue.
The somatopleura forms connective tissue
The notochord causes the part of the somite lateral to it from both sides to form
cartilage (doesn't happen in amphioxus, which simply maintains it notochord). The
cartilage closes around the notochord and becomes the future vertebrae, initially
cartilagous and later made of bone. This part is called the sclerotome.
The upper part of the somite becomes the myotome (develops into segmented muscles
around the vertebrae). The later part of the somite will become the dermatome,
forming connective tissue.
Growth and Differentiation
Infraphylum Gnathostomata
Class Osteichthyes – origin of the modern digestive system
Digestive system
The digestive system is fundamentally the same in fish and humans. It originates in
the splanchnopleura.
The digestive system has to be able to mechanically degrade the food in order to
increase surface area for chemical digestion. The enzymes are proteases that break
down materials such as proteins into fundamental amino acids. The digestive system
most also move food along it, absorb the nutrients and excrete waste.
Fish have homodontic teeth on both jaws, that are meant only to break food down into
large chunks, which requires a large pharynx and esophagus.
Teeth originated from the exoskeleton, resulting in placoid teeth. There are no
salivary glands in aquatic forms.
Mammalian teeh are heterodentic and sit in small craters – thecodontic teeth. This
doensn't occur in other animals save for alligators. Avians lack teeth due to
adapatations to flight, but retain the potential to develop teeth.
Evolutionary trends are towards the reduction of the number of gills, and fish use
these for breathing, not food filtering.
The large intestine is useful for storing large amounts of food. The intestine is
comprised of two parts:
 Cardiac/fundic  Pyloric The intestine releases hydrochloric acid in order to kill bacteria and perform
hydrolysis. The inner part of the gut is lined by epithelial cells which excretes a
mucopolysaccharide which reacts with the acid and protects the gut. This protection
isn’t perfect, so an auxiliary mechanism causes rapid division of the epithelial cells.
This mechanism exists throughout the length of the digestive system. Pepsin works in
this acidic environment.
The mesodermal splanchnopleura creates smooth circular, longitudinal and oblique
muscles around the gut. A pyloric sphincter separates the two parts of intestine and
prevents food from rushing into a much smaller space at once.
The next area is called the duodenum. Food here is digested much faster because of
two large exocrine glands: the liver and pancreas (two pancreae in fish and human
embryos):
 The pancreas secretes most of the enzymes associated with digestion, as well
as antacids since its enzymes operate in alkaline conditions.
 The liver originated in the digestive tract and originally was used to create bile
(stored in higher vertebrates in the gall bladder). Bile is used as an emulsifier
to increase the surface area of fatty substances. The liver serves other
functions, such as flotation in fish by aggregation of fat.
There are four ways in which surface area is increased:
1. Longer intestine (longer in herbivores than carnivores)
2. Creation of creases in the gut and intestine called plicae
3. Lining of the plicae with small finger-like structures (villi)
4. Lining of the villi with microvilli
A spiral valve increases the surface area further and drains into the rectum which
opens into the cloaca (which concentrates the liquid waste, solid waste and sex
products).
The rectal gland above the rectum does not aid digestion but rather desalinizes the
blood (much salt enters the system from the water) and deposits it in the rectum. This
occurs in sharks, while in bony fish the gills are in charge of desalinization.
Respiratory system
Developed from the pharynx in all cases. Breathing can be either aerobic or anaerobic
(redox reaction based). An anaerobic system is energetically inefficient but doesn't
require oxygen.
Gills are the staples of fish.
Amphibians breathe through lungs and via diffusion through skin.
Reptiles, birds and mammals breathe through lungs exclusively.
There are seven gills in most vertebrates. The first becomes the jaw, the seond
becomes the tongue arch.
The mouth forms via the recession of the endoderm and ectoderm towards each other,
which connects the pharynx with the external environment.
Along the sides of the head, this happens as well, forming gills slits. In sharks there
are five. A bone forms inside the gill, dividing it into two hemibranchae, which
together form a holobranch. The epithelial cells lining the gills absorb the oxygen and
exchanges them with the blood vessels also form by the mesoderm.
In order for there to be efficient diffusion, there must be a large surface area (A), a
thin epithelial layer to minimize diffusion distance (l), long transfer time (dt) and a
large concentration gradient (dC):
 Surface area: increased by forming horizontal filaments (‫ )עלעל‬that have
vertical lamelae growing upon them.
 Diffusion distance: epithelial cells are stretched very thin over the lamelae and
filaments.
 Transfer time: Smaller exits for the water to create long contact time.
 Concentration gradient: oxygen-poor blood flows opposite to the direction of
water (counter-current)
Muscular pharynx for propulsion of water through the gills.
Urogenital system
The mesoderm between the splanchno and somatopleura is called the intermediate
mesoderm and forms the urogenital system.
Each segment develops a tubule called a nephron. Its opening is to the coelom and is
called a nephrostome. Every nephron has a small indentation called a Bowman
capsule which holds onto a bulb of artery (both coming in and going out) called a
glomerulus, and together form a Malpighi corpuscle, the basic filtration unit. This is
the basic structure of the pronephros. Only the lamprey larvae use this as a functional
kidney. The pronephric duct connects the pronephros to the cloaca.
In every segment there is a pair of nephrons open to coelom.
In the mesonephros (opistonephros is the rear part in sharks), located in the middle of
the body after development from the pronephric duct, several nephrons develop in
each segment, but few have a nephrostome opening to the coelom. The mesonephros
exists in adult lampreys, fish and amphibians. In amniotes, the mesonephric duct
continues further and forms the active kidney, the metanephros.
None of the metanephros nephrons have nephrostomes, and they are much greater in
number. The nephrons reabsorb water and nutrients.
The part of the mesonephric duct in which waste is transferred is called the Wolffian
duct.
A genital ridge forms from the intermediate mesoderm and is called an indifferent
gonad. If it becomes an ovary the center will atrophy and the perimeter will develop,
the opposite is true for a testicle. There is migration of endodermal cells through the
mesentry into the indifferent gonad which become the germ cells. They always
migrate to the developed part (depending on the gonad).
An oocyte will be covered by mesodermal cells (collectively called a follicle). The
follicles develop individually and expells the egg into the coelom. The Mullerian duct
(oviduct) forms a funnel into the coelom that receives the oocyte. The Wolffian duct
atrophies.
The male reproductive system uses the Wolffian ducts to expel semen. The Mullerian
duct atrophies.
A primitive amiotic sac exists in fish, and the embryo gets its nutrients from the
mother.
In mammals the Mullerian ducts fuse at the end. In higher mammals, the "horns" of
the uterus meet to form the uterus as we know it.
During fuckies, the semen is ejaculated into the pre-cervical area and migrate up to
the Mullerian tubes to fertilize the oocyte. The zygote migrates to the uterus and
reaches it as a blastocyst.
The vascular system
Initially there are angiogenic cell clusters, some cells of which later form an amorphic
system of tubes, while others form blood cells. The tubes later fuse so that in to
ventral area there is a large artery, while two dorsal arteries form and fuse in the back
towads the tail. They branch off into the organs which in turn send arteries towards
the ventral artery.
The ventral blood vessel is the parallels of veins. Where there is a heart, it forms from
the ventral artery folding into an S shape. Four areas are formed:
Organs  Sinus venosus  atrium  ventricle  Conus arteriosus  ventral artery
 gills  dorsal arteries.
Blood flows from the sinus venosus to atrium to the chamber to the ventral artery
which absorbs oxygen. The sinus venosus degenerates in higher vertebrates.
The heart has its own pacemaker (sinoatrial node), independent of the central nervous
system.
Portal systems, where one blood vessel enters and exits, do not replace the normal
artery-vein system.
Arterial types: gills and glomeruli
Veinous types: Portal renal vein (kidneys) does not exist in mammals, another one
filtered by the liver, a third in the pituitary gland.
In fish hearts, sometimes oxygen rich blood is pumped, sometimes it is oxygen-poor.
In amphibians, there is partial separation. In reptiles it is more advanced. In alligators,
birds and mammals it is complete.
Superclass Tetrapoda
Class Amphibia
The advantages of climing on to land were high concentrations of oxygen and plenty
of food. Several problems stood in their way:
1. Lack of water to maintain cellular function.
2. Bearing of weight in a lighter medium (air)
3. Breathing oxygen in a gaseous phase
4. Thermoregulation – temperature isn’t steady as it is in water. Homeothermy
requires a fast metabolism.
5. Sensory – absorption of non-soluble molecules, maintaining wetness of the
eye and perceiving alternating levels of light, perceiving sound waves
transmitted through air.
6. Embryonic development – requires an aquatic environment.
Solutions:
1. Amphibians live their lives next to an aquatic environment. Those who
venture further away have glands that keep their skin moist. To prevent
aggregation of pathogens, they secrete germicidal agents as well (Magainin).
They also developed salivary gland for lubrication.
2. The first solution was reduction of weight by fusion of bones. Illium, ishium
and pubis – three hip bones fused into one to relieve pressure off the smaller
bones. To keep body mass above the ground, the pectoral and pubic fins
became legs. Muscles – adductors and abductors (‫)מקרבים ומרחיקים‬, flexors and
extensors (‫)כופפים ופשוטים‬.
3. Since the skin is moist, oxygen can dissolve into it and all that's required is a
circulatory system to lead it away. The air sac underneath the mouth is
covered with blood vessels and is inflated. Lungs develop in lower pharyngeal
area, the primary organ being the trachea that branch off into two bronchii,
each of which branch off into many bronchioli that ends in alveoli. These are
covered by small blood vessels.
Tidal breathing means that breathing is inhaled and and then exhaled, which is
less efficient.
Nostrils become open into the pharynx in order to breath while holding on to
food.
Two circulatory systems developed: heart body heart and heart lungs heart.
The right atrium received the blue blood, the left atrium receives the red blood
and the ventricle is still one. A spiral structure separates the blood types more
or less. In reptiles division of the ventricle begins.
Six pairs of arterial arches exist: the first two degenerate, the 3rd becomes he
carotid artery, 4th becomes the systemic artery (goes to the body through the
dorsal arteries), the 5th connects the 4th and the 6th, and the 6th becomes the
pulmocutaneous artery. If 5th is open, blue baby syndrome.
4. Not solved (poikytherms/ectotherms), only by slight behavioral means. Three
types of chromatopores are developed: melanophores that absorb light and
protect from UV rays, xanthophores for camouflage and reflective iridophores.
Hibernation is also a mechanism
5. The area inside the nostrils secretes a fluid that dissolves signaling molecules.
Hearing is improved by focusing sound onto on point. One of the gills slits
closes up and the outer ear becomes the ‫אוזן יצונית‬, an internal bone ( ‫עמודית‬
‫ )השמע‬touches it on the point. Lagena - three arches that are used for balance
in the inner ear.
Lacrimal glands keep the eyes moist. Eyelids and blinking evolve. Eye
muscles evolve, to regulate the amount of light entering the eyes.Color vision
evolves.
6. Solution not given, metaolous development. Remained next to bodies of water
where they reproduce. Most of the embryological development occurs after
hatching. Metamorphosis occurs and adaptations for land are made.
The zygote has a large fertilization membrane which focuses light into
pigments in the animal pole to energize development. The gray crescent
develops opposite to the sperm's entrance and signifies the movement of
matter inside the cell. As signified by cloning, these materials are unique to
the oocyte. Cleavage is radial holoblastic of a mesolecithal cell. Before
hatching into the water, there is no mouth, but there is an anus and gills. Initial
nutrition is vegetative.
Order Anura
jumping motions
Order Urodela
move primarily with their tail.
Order Apoda
snake-like motions.
Superclass Amniota
Class Reptilia
Reptiles have rapid ectodermal divisions that creates a layer of dry dead cells for
protection (keratin). Underneath there are bony plates for protection. They have the
same chromatophores as amphibians and lack sweat glands.
Loss of limbs and limb-supporting systems is secondary, as in snakes.
The skull develops in size and hinges powerful muscles upon (crocodiles), allows
crushing of prey. Homodontic teeth (thecodontic in crocs) do not allow chewing. Only
mammals have a lower jaw made of one bone.
The condyle (‫ )פול‬connects the spinal column with the skull creating a spherical joint,
allowing for more varied motion as opposed to amphibians. This is true in aves as
well. Mammals and amphibians have two.
The snake jaw is connected via tissue, which allows for massive opening of the jaw.
This creates a weaker skull, which caused the development of venom glands. Since
the prey blocks the trachea, it's moved up into the mouth.
Breathing is done entirely via lungs, so the alveoli have a greater surface area. Air is
moved via rib movement. Air is sucked in by creation of a local sub-pressure region
(lizards and snakes). Turtles and crocs pull the lower part of the lungs downwards.
Croc breathe with a diaphragm. Tidal breathing.
The vascular systems is further developed, there is a near complete division of the
ventricles.
Thermoregulation isn’t solved in reptiles, is mostly on a behavioral basis.
Reptiles have the middle ear like the amphibians, and some have a Jacobson's organ.
Tree snakes have sharp vision. Pit organs allow snakes excellent vision in he infrared
spectrum.
The kidneys are metanephric. To conserve water, nitrogenous waste is excreted as
uric acid. Reptiles that live near or in water also excrete urea and ammonia. There is a
veinous gate system.
Osmoregulation is achieved in turtles and crocs by special glands in the eyes and
nostrils that excrete salts in a manner similar to fish.
Amniotes have 12 nerve pairs in the skull.
To solve the problem of embryonic development, which required internal fertilization,
the male inserts his penis (an extension of the cloaca) into the female. The egg travels
through the oviduct which covers it with nutriets and it is later covered by a hard
mechanical defensive layer, usually calcium based. Fertilization temperature
determines the sex, not genes.
Turtles
Order Squamata (lizards and snakes)
Order Sphenodonta
Order Crocodila
Class Aves
Their bodies are entirely adapted to flight, which is why all avians body are very
similar. Evolved from reptiles.
They have one condyle, like reptiles, and several jaw bones. Quadrate (upper jaw)and
articular (lower jaw) connected by a joint. Like amphibians, one bone in the middle
ear. Archaeopteryx was probably an evolutionary forerunner.
Uric acid is excreted to prevent water loss. The have scales, like lizards, though most
have become feathers. On the legs they are many times still present.
Flight allowed the exploitation of a new niche with lots of food, escape from
predators, new attack vector. Extensive migration to better conditions.
Feathers are a common to all avians. Feather protrude initially in sheaths in a scalelike fashion, a expand from the hard middle part, rachis or shaft. Oblique slits cut the
feather along is length, and each barb is separated from the next by barbules to
maintain cohesion.
Feather types
Flight feathers
Contour feathers
Filoplume feathers (‫ )חוטית‬- sensory
Down feather (‫ )פלומה‬regulate temperature
Powder feather – degrade into a powder, repel water
Feathers change gradually to maintain balance. Different rates of change in each
season. Some feathers are colored by pigments, others are iridescent.
Adaptations to flight
Feathers.
The skeleton has to be strong to stand the winds yet light to decrease payload. The
anterior limbs became wings, the posterior remained legs. To keep balance, avians
have a horizontal hip to adjust the center of gravity for upright posture.
The skull bones became thin and teeth were lost. Avian bones have vertical supports
inside to compensate for decreased density.
Arm and leg bone are fused (carpometacapus and tarsometatarsus). The three hip
bones fused into the synsacrum.
The sternum widened and the crista was formed to allow attachment of muscles. The
clavicles became the furcula.
Pectoralis major lowers the wing, pectoralis minor raises it. To prevent heat loss, leg
muscles were moved towards the body and the legs were covered in scales.
The heart is 15% of the avian's body weight, and shows complete separation between
ventricles and atria. The heart beats hundreds of times per minute. Erythrocytes are
nucleated, unlike mammals and like all other vertebrates. The left systemic artery
degenerates (opposite in mammals).
A crop in the pharynx can store food. There is no aggregation of feces or urine to
lessen the payload. One Mullerian duct and ovary degenerates. Males have two
Wolffian ducts as sperm are light. Salt glands above the eye perform ionoregulation.
Gas exchange happens mostly during inhalation. In avians, the lungs contain 4 pairs
of air sacs and one lone sac in which gas exchange does not occur. Air rushes in,
washes the lungs and gas exchange occurs, enters the sacs, and during exhalation
washes the lungs again, during which exchange occurs.
The lung isn't made of cysts but rather tubules.
The breathing mechanism is cross-current, which allows for the lungs to consistently
be washed by air.
Inhalation 1: Air enters the lungs and the posterior sacs.
Exhalation 1: Air from the posterior sacs is flows into the lungs, and since the anterior
sacs are also compressed, the air from the lungs has nowhere to go.
Inhalation 2: New air enters the lungs and posterior sacs. Old air from the sacs moves
to the posterior sacs.
Exhalation 2: The air in the posterior sacs moves to the lungs (can't flow out due to
high pressure) and the air in the anterior sac is exhaled out.
An arterial portal system exists in the kidney (glomerulus), a veinous one exists in the
liver and in the pituitary gland (for the hypothalamus to regulate it), as in all
vertebrates.
The kidney portal system exist in fish, amphibians, reptiles and partially in avians.
Using a valve, blood can either be filtered by the kidneys or continue to the heart for
faster metabolism.
Class Mammalia
Caring for young – develop of the placenta, breastfeeding, protection.
Advanced systems in the adult – development of the neocortex, homeothermy, hair.
Monotremes
Have a cloaca, no penis. Lay eggs. No nipples (milk is excreted onto the skin). Adults
have no teeth and the shoulder belt contains many bones.
Marsupials
Have a similar placenta to placental mammals. The young are born early and move to
the marsupium, where they have find a nipple. The time spent in the marsupium is six
times the time spent in the placenta.
Placentals
The embryo develops from the inner cell mass. The outer cell mass are shed.
Nipples develop ventrally in pairs (2-12). The ectorderm sinks in and branches off and
the end cells become lactic glands. Sinuses store milk produced in the glands. In
marine mammals, the milk is inected by pressure into the offspring's mouth.
Prolactin is the hormone that mediates the activity of lactic glands. It causes the
glands to develop further, synthesize and secrete milk. The sinus enlarges.
Sucking stimulates the release of prolactin causes a feedback loop.
Keratin-based hair develops initially to thermoregulate. Additional functions include
camouflage, mechanical defense, inter- and intra-special communication and sense.
Marine mammals have degenerate hair.
Hair types include soft hair and hard hair for defense, such as in porcupines and
hedgehogs. Hair develops by pushing ectoderm upwards, which dies and becomes
keratin.
The arrector pili extends the hair for thermoreulation (goosebumps).
The epidermis is a dead layer, the dermis gets bloodflow and nerves, which is why the
hairs are anchored in the dermis.
Newly developed glands include sweat glands (non-analogous to the amphibian type)
which also ionoregulate. Sebaceous glands lubricate hair. Mammary glands produce
milk. Scent glands are developed for communication and protection (skunks).
Increase in size of the cortex is a major development.
The diaphragm develops.
The ventricles are now completely separate. In mammals the right systemic artery
degenerated. The veinous portal system is gone, and is compensated by changing
nitrogenous waste into urea.
Osmoregulation
In salt water, osmotic pressure is maintained by osmoconformation by keeping
dissolving urea in the blood. An alternate mechanism is by desaltization of the blood
(shark's rectal gland or excretion via gills in fish).
In freshwater, osomoregulations is done by absorbing less water in the nephrons.
In terrestrials, water isn't lost via the skin (sweating is thermoregulatory, not primarily
osmoregulatory), water is reabsorbed through the kidneys. Henle's loop allow better
absorption.
Ear structure
Pinnae focus sound waves, three bones transfer sound. The cochlea develops to allow
more contact area for neurons.
Reproduction
Males have a penis that channels urine and sperm. Females have separates ducts for
sex and excretory products.
Skeleton
In all mammals there are 7 vertebra in the neck. The jaw is jointed by the dentary
(lower jaw) and the squamosal, as opposed by the quadrate-articular configuration of
lower animals. A fossil intermediate has been found.
The limbs are now ventral, not lateral. Allows for erect posture. Less bones in the
pelvic and pectoral girdleand the skull. The spinal column is divided into neck,
thorax, waist, hip and tail.
The roof of the mouth separates the nasal and oral cavities, so mammals can breathe
and feed simultaneously.
Heterodont and thecodont teeth exist, and teeth change twice (diphydont). Chewing
mucles develop.
Movemement is dorsoventral, not dorsolateral like in fish and reptiles.
Phylogenesis of the skeletal system
Three primary parts:
Skull cranium – contains the neurocranium and viscerocranium.
Trunk – spinal colum, ribcage and sternum.
Limbs
The mammalian skull has less bones and the ribs end after the thorax. The pectoral
fins became the forelimbs, pelvic fins become the hindlimbs.
The skeleton serves as a support for the muscles. Segmentation weakens the skeleton
but allows greater motion. The skeleton also protects internal organs: the skull
protects brain, the vertebrae protect the spinal cord, ribs protect the lungs and heart,
the hip bones protect the ovaries and uterus.
Hematopoietic stem cells originate in the bone marrow and differentiate into blood
cells. Calcium and phosphorus are stored in bones.
Types of skeleton
Hydrostatic – water pressure.
Solid skeletons are made of calcium carbonate or sodium phosphate. When reduction
of weight was necessary when vertebrates moved onto land, skull bones fused and
niches appeared to reduced weight and allow anchoring of muscles.
Exoskeleton – Chitinous in insects, calcium phosphate in vertebrates. Can be one or
several pieces. Primitive vertebrates had an exoskeleton, but it was too cumbersome.
It was made of three layers: compact, spongy, compact. The external layer was the
precursor of teeth. The teeth originated in the mesodermal dermatome, making it a
dermal skeleton. Fish covered it with ectodermal scales.
The remnants of the exoskeleton in vertebrates include teeth, scales and armor.
Endoskeleton – The vertebrae form around the notochord. Ribs anchored onto the
vertebrae as well as the pelvic and pectoral girdles. Enchondral bones form first in
most cases (dermal bones form sometimes, originate in the exoskeleton).
The neural crest cells form the skull and gill slits (ectodermal in orign, not
mesodermal like the rest of the skull).
The sclerotome forms the cartilage around the chorda and the spinal cord. The lateral
somatomesdoderm forms the ribs. The part that connects to the sternum remains
cartilagous.
The formation of bone from a cartilagous precursor
Based on hyaline cartilage. Blood vessels enter the middle part and the blood carries
chondroblasts which build cartilage and chondroclasts which destroy cartilage in the
middle part. Osteoblasts trigger the growth of bone in the middle part (diaphysis).
This process later repeats in the peripheral parts (epiphysis). In between is a
cartilagous plate that grows and expands and is extends forming more bone in the
same process. Towards the end of growth, this plate is destroyed.
This process occurs in the limb bones as well are vertebrae.
While the bone grows, osteoblasts enter the diaphysis and kick some osteocyte ass
while the epiphysis contnues growth, causing the stretching of the bone. The hollow
is the bone marrow, occupied by hematopoietic stem cells. The connective tissue
around the bone is called the periost. The layers are periost, compact bone, spongy
bone and bone marrow.
Bone forms around blood vessels in circular structure to form the osteon/Haver's
canal (compact bone). This is by osteoblast aggregation around the vessel and
excretion of bone forming materials. Once it stops, it is called an osteocyte. The blood
vessel oxygenates the layers via Volkmann canals, inner and outer rings. Outer rings
are osteoblastic. Bone formation and destruction is a system in Dynamic equilibrium.
When the blood leaves the bone (the bone marrow is the last stop), it leaves with new
blood cells.
The spongy bone is made of small plates distanced apart.
The notochord induces the segmentation of the somite pairs. The sclerotome pairs
surround it and the nerve tube, and serves as the basis of the vertebrae. The myotome
develops the segmented muscles and attaches to the vertebrae.
Neurocranium and viscerocranium
The jaw formed from the first gill arch, the second became the base of the tongue. The
last five serve as gills in fish and the tracheal cartilage in tetrapods.
The brain developed centers for different centers which are protected by the skull,
formed of neural crest cells. The trabeculae and parachodalia close the braincase
from beneath.
The hyomandiblula is a joint bone that connects to the middle ear and serves as the
hearing bone.
The nervous system
Nerves serve to collect information (sensory nerves), while others relay information
(motoric nerves).
Advantages: Quick and precise response to stimuli.
Disadvanages: Requires a large and complex network of cables, as well as a
consistent signal.
The endocrine system is based on glands that secrete hormones into the bloodstream.
Hormones are either proteins, peptides and amino acids and its derivatives, or rather
steroids.
Advantages: Utilizes an existing network blood.
Disadvantages: No spatial or temporal control after release into the blood system.
The chorda causes the ectoderm above it to sink inside and form the neural groove,
which closes creates the nerve canal. The tube is initially open in both ends
(neuropores), but later closes, remaining hollow. The dorso-lateral cells remaining are
the neural crest.
The anterior part swells and these three swellings become the brain (pro-, meso- and
rhombencephalon). In fish onwards, the anterior and posterior swelling divide in two:
Cerebrum
Diencephalon
Mesencephalon
Cerebellum
Medulla oblongata
Spinal chord
These are all filled with CSF, so a lumbar puncture can inform us about the brains.
Due to sclerotome growth around the neural canal, despite the brain being ectodermal,
the surrounding tissue is mesodermal.
During segmentation, neural crest cells migrate laterally, forming one pair of spinal
ganglia in each segment, adjacent to the spinal cord and remain inside the vertebrae.
Others, which migrate further, forms sympathetic ganglia. These are not segmental.
Other neural crest cells migrate far away unevenly, creating parasympathetic ganglia.
The cells forming the perimeter of the neural canal divide rapidly both inwards and
out, causing the shrinking of the canal. These cells divide into two types:
Neuroglia – most cells become these, and serve as supports and can further
differentiate:
Astrocytes – form the blood-brain barrier.
Oligodendrocytes – form the myelin sheathes on the neurons.
Microglia – macrophage analogs.
Ependyma – pad the central canal of the neural groove.
Neurons – contain dendrites and axons.
Dendrites – incoming signal
Axons – outgoing signal
Neural crest cells, called in this case Schwann cells, cover the long branch (axon or
dendrite) and wrap themselves around the branch, forming myelin sheaths. This
serves to protect and increase speed of conductivity of the electric signal.
Neurons can be either bipolar or multipolar (10,000 is the largest known number).
The junction between a neuron and another cell is called a synapse. There is no actual
contact between the two cells, a synaptic cleft separates them. The signal is
transferred chemically via neurotransmitter, released from presynaptic vesicles.
Differentiation into a neuron requires a further differentiation:
Somatosensory and viscerosensory nerves or somatomotory (controlled nervous
system) and visceromotory (autonomous sympathetic and parasympathetic nervous
systems).
The cells forming perimeter of the nerve canal. The cell bodies (grey matter) migrate
and the fibrous (white matter) and stays outside. The cells agglomerate as two pairs of
"horns", the dorsal being sensory, the ventral being motoric. Outside the vertebra, the
cables of sensory and motor cells are joined together.
Reflexes evolved to override the brain in order to prevent damage (touching a hot
surface). Learning, both cognitive and kinesthetic, is based on synapse formation.
Meninges
Piamater – cyclostome and onwards.
Arachnoid – Mammals.
Dura mater – fish and onwards.
Sympathetic (thoracolumbar) and parasympathetic (craniosacral) systems
Sympathethic
Ganglia in some segments, outside the vertebrae, reaching out to the thorax and
abdomen, short preganglion strand (acetyl choline) and long postganglion strand
(noradrenaline), myelinated,
Parasympathetic
Ganglia all over the place, all connected to the brains, long preganglion strand (acetyl
choline) and short postganglion strand (acetyl choline), unmyelinated
The two systems are antagonistic. The parasympathetic is active during rest and the
sympathetic system is active during non-routine events.
Phylogenesis of the nervous system
In amphioxus, there is a nerve chord, no proper brains. There is no joining of the
"horns", similar to our higher brains.
The number of horns is 31 pairs, grey matter in the middle, white matter on the
outside, sensory in the dorsal side, motory in the ventral. In the higher brains the
center is white matter, perimeter is grey.
Craniates show the development of brains (five in fish and onwards). Amniotes have
12 pairs of neurons in the brains. The mesencephalon serves as the basis for sight
The medulla oblongata induces the development of the auditory system. The brains
developed as center of sense.
The cerebrum
The large brain. Made of two hemispheres.
It originated in cyclostomes where it was served soley as an olfactory center
In fish, it developed into two pallia, paleopalium and archipalium. In the anterior part,
basal nuclei form which send branches to the mesenchephalon, which was the
primary brain in fish.
Reptiles – the basal nuclei become highly developed, which become dominant nad
expands into the ventricle. The archipalium is pushed aside.
Avians – further developed the basal nuclei. The inner part is the caudate nucleus
(tail-bearing nucleus), at the end of which is the amygdaloid (center of pleasure). In
the middle of it are the putamen and the globus pallidus. Higher birds have another
layer covering the basal nuclei – hyperstriatum.
Mammals – also developed the basal nuclei (called striatum), but invested more
energy in development of the neopallium. This became very developed, and began to
take control over the basal nuclei as well as other brains. It began to push the
paleopallium and archipallium. The archipallium was shriveled up and was known as
hippocampus. The neopallium became condensed and rough. The paleopallium
becomes pear shaped – corpus pyriformus, still the olfactory center. Mammals
developed an additional layer above the entire neopallium, the necortex (80% of the
brain in man).
A longitudinal fissure separates the left and right hemispheres. Smaller fissures are
called sulci, the bulging areas are called gyri. The central sulcus divides the
prefrontal and parietal lobes. Behind the parietal is the occipital lobe (visual cortex
and visual association area), while the temporal lobes (auditory cortex and auditory
association area) are located at the temples. These cortexes are interconnected.
The area anterior to the central sulcus is the primary motor cortex, parallel and
posterior to it is the primary somesthetic cortex, the first controlling motion, the latter
receiving sense. These areas are paired up and pertain to areas in the body, each areas
size depending on the complexity of the area's momement and sensitivity.
Each hemisphere controls the opposite side of the body. The horizontal connections
between them are called the corpus callosum.
The hippocampi (archipallium) of the two hemispheres connect to each other and then
to the hypothalamus, the metabolic center. Together with the amygdaloid, they form
the limbic system.
All the other brains are called the brain stem.
The diencephalon
Still controls the eyes. Originally sent two branches, left and right. Has two more
upward branches that originally served as additional eyes. The parietal eye still exist
in the sphenodon, but is degenerate in all others. The pineal eye became the pineal
gland which secretes melatonin (regulator of the photoperiod), and still contains
photoreceptors.
A fifth branch connects to the hypothalamus, which regulates activity via hormonal
discharge, as well as controls the pituitary gland.
The dienchephalon controls essential functions and has thus changed very little.
Mesencephalon
Tectum – sensory area (dorsal)
Tegmentum – motoric area (ventral)
Cerebellum
Pyramidal tract – the railing for the somatomotor nerves. Connect to the spinal cord.
It helps coordinate complex movements, so animals with complex movements have a
more complex cerebellum.
Medulla oblongata
Serves as the breathing, balance, blood pressure and hearing center. Sytenic. The
cortex can override some of its functions. In extreme conditions, the override is
reversed.