Download Concept 1: sponges are basal animals that lack true tissues

Biology 102
Chapter 33
Invertebrates
Concept 1: sponges are basal animals that lack true tissues
Sponges are basal animals ( arise from the
base of animal tree) and lack true tissues .
Sponges belong to phylum Porifera and are thought to be monophyletic (has
only one ancestor ) .
Most of these species are marine (live in water ) and range from millimeters
to meters in length .
Sponges are filter feeders (feed on suspended particles in water) , water
goes through pores into a cavity called spongocoel and goes out through an
opening called osculum (some sponges have several oscula (plural for
osculum ) .
Sponges cells ,layers :
1- Choanocytes: interior to the spongocoel and flagellated used to engulf
bacteria and other particles by phagocytosis.
2- The mesohyl: the wall of sponges consists of two layers separated by a
gelatinous matrix called the mesohyl.
3- Amoebocytes : cells that move through the mesohyl (use pseudopods )
and do various functions:
a) Digest food from water and Choanocytes.
b) Carry nutrients to other cells.
c) Manufacture skeletal fibers in the mesohyl (made from calcium
carbonate or silica), other sponges produce more flexible fibers made of
a protein called spongin.
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d) They are totipotent ( they are capable of becoming any other type of
sponge cells).  see figure:
Most sponges are hermaphrodites (an
individual has both sexes) and produce both sperms and eggs
.They can also cross fertilize each other if the sperm is released to
the water.
The fertilized egg forms a zygote which
develops into a flagellated moving larvae which then settles to a
substrate.
Sponges produce many antibiotics such as
cribrostatin (‫ )سيريبروستاتين‬which can kill cancer cells and penicillinresistant bacteria streptococcus.
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Concept 2 : Cnidarians are an ancient phylum of Eumetazoans :
123456-
Properties of cnidarians:
Most of them are diploblastic and have radial symmetry.
They have a central sac that resembles the gastrovascular cavity.
A single opening in the gastrovascular cavity is both mouth and anus.
They are predators and use tentacles around their mouth to capture the
prey , also digestive enzymes are secreted into the gastrovascular cavity.
They have no brain, and the nerve net is associated with sensory
structures around the body, thus it can respond from any direction.
Their tentacles are equipped with cnidocytes (cells unique to cnidarians)
and their function is defense and capturing preys. These cells contain
organelles called cnidae ( some specialized cnidae called nematocysts
contain a thread to poison the prey).see the figure 
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7- The gastrovascular cavity acts as a hydrostatic skeleton.
8- Cnidarians have two shapes : shown in the table
Properties\shape
Polyp
Medusa
movment
Sessile ( doesn’t
move a lot)
Aboral side is
downward
Motile
Hydrozoans
(Hydras \sea
anemone)
Scyphozoans
(Jellies) \
cubazoans (box
jellies)
Aboral side ( the side
opposite the
mouth\anus opening)
example
Aboral side is
upward
A hydrozoan called the sea wasp is very poisonous and may
lead to respiratory failure and cardiac arrest and death
within minutes.
Some of the cnidarians change their forms in their life time.
See the life cycle of the hydrozoan obelia which has the two
shapes during his life. See the figure
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Bilaterians are divided into three clades:
1- Lophotrochozoans (concept 3)
2- Ecdysozoans (concept 4)
3- Deuterstomia (concept 5 and chapter 34)
Concept 3: lophotrochozoans (triploblastic, bilateral animals):
So named because some of them develop a structure called lophophore, and
others go to a distinctive stage called trochophore larva and others have
neither of these.
A lophophore is a crown of ciliated tentacles for feeding. See the figure 
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Lophotrochozoans have the widest range of body forms and include 18
phyla (you will study only 3 of them, flatworms, mollusks and annelids).
1- Flatworms( phylum Platyhelminthes):
They include parasitic and non-parasitic species and named after their flat
body (dorsoventrally) and range in length from few micrometers to more
than 20 meters long .
They are triploblastic acoelomates with large surface area to exchange gases
by diffusion such as ammonia.
They have an excretory apparatus that consists of protonephridia (a network
of tubules with ciliated structures called flame bulbs).
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Flatworms have only one opening in the gastrovascular cavity.
Flatworms are separated into two lineages, Catenulida and Rhabditophora.
Catenulida is small clade of only 100 species and reproduce asexually by
budding and form a chain of identical individuals (called chain worms).
Rhabditophora is a clade of 20000 worms and we will study them in detail.
Free living species of Rhabditophora :
They are predators and scavengers and the
most known are Planarians (Dugesia).
They move by cilia on the ventral surface or
gliding along mucus and some use muscles to move in water ( undulating
motion ).see figure 
Planarians are hermaphrodites (They produce
sexually and asexually ).
They produce asexually by fission and sexually by cross fertilization.
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Parasitic Rhabditophora include Trematodes and tapeworms :
Trematodes: they alter between sexual and
asexual stages and require an intermediate (a snail) before infecting the host
(a vertebrate), they case a disease called Schistosomiasis and include
symptoms like pain, anemia and diarrhea
They evade the immune system of a host by
mimicking its surface proteins which creates a camouflage for itself, thus
manipulating the host immune system to tolerate its existing as a parasite
and can live more than 40 years.
See figure 
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Tapeworms:
They consist of Scolex armed with suckers and hooks to attach to the host
intestine.
They lack a mouth and a gastrovascular cavity.
Posterior to the Scolex there are units called Proglottids (sex organs), which are
sacs that contain fertilized eggs that get out in feces to enter an intermediate host
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(pigs or cattle) and encyst in their muscles. They infect hosts by eating
undercooked meat containing cysts. See figure 33.12 page 691
2- Molluscs , soft bodied animals with hard shells of calcium
carbonate:
Molluscs include snails, slugs, oysters, clams, octopuses and squids.
Some Molluscs have reduced shells like octopuses.
Molluscs are coelomates with three major parts: foot, visceral mass, and a
mantle. See the figure 
Most of Molluscs have separate sexes and many snails are hermaphrodites,
mollusks include a ciliated larvae (trochophore) in their life cycles.
Phylum Mollusca has eight clades and we will study only three, gastropoda,
bivalvia and cephalopods.
Gastropods (snails and slugs) :
Most gastropods have shells (secreted by glands at the edge of the
mantle) which have many functions including protection from injury and
dehydration and defense from predators by hiding inside the shell.
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They feed on plants (herbivores) and some of them are predators, the
teeth in the radula are modified and act as poison darts.
Aquatic snails have gills while terrestrial snails use their mantle cavity as a
lung. They either move by muscular foot or cilia.
Bivalves, a clade of aquatic species (clams, oysters, scallops):
Their shells are divided into two halves that
have powerful muscles to draw them together to protect the animal’s
soft body. see figure 
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They are suspension feeders and have no
radula, water goes in through a siphon and the gills are used for eating as
well as gas exchange.
They prefer sedentary non motile life. But
some are limited motile.
Cephalopods, marine predators:
They use their tentacles to capture prey and poison it with their saliva.
Their foot was modified into an excurrent siphon used for moving by
firing a jet of water and steer by moving the siphon.
They have a reduced or internal shell, the only cephalopod with an
external shell is chambered nautiluses (ammonites).
They are the only clade of Molluscs which have a closed circulatory blood
system. ( all others have an open system)
Some squids reach a length of 14 meters .
Annelids (a phyla of segmented
worms):
Annelids are coelomated worms which have a length from 1mm to more
than 3 meters.
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Annelids used to be classified into three groups:
Polychaeta
1- Oligochaeta
2- Hirudinea (leeches)
Chaeta : hair like extensions made of chitin grow from the segments of the
worm
But further studies put the first two groups together and the new classification is
as follows :
Annelids are grouped into two clades:
1- Errantians ( mostly marine living in seas and oceans) :
o Mostly mobile either by crawling on sea floor or swim among the
plankton which are small organisms.
o Some of them are immobile like Platyneries (species used for studying
neurobiology)
o Mostly each segment has a pair of parapodia used for locomotion
(movement). Each parapodium has numerous chaeta.
o Parapodia are rich in blood vessels and function as gills
2- Sedentarians:
o Less mobile species and use gills or tentacles for filter feeding.
o They include oligochaetes which contains both leeches and earth
worms.
Leeches: (Sedentarians)
1- Mostly live in fresh water but some are terrestrial (live on land).
2- They range in length from 1-30 cm . they are predators and feed on
vertebrates and some them are parasites that feed on animal blood.
3- Leeches secrete an anesthetic (‫ ) مخدر‬on the skin of an animal. They also
secrete a chemical called Hirudin which prevents the blood from clotting or
coagulating.
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4- They suck blood ten times their weight and can last for month without
another meal.
5- Leeches are used in medicine as bloodletting (suck extra blood) after
surgeries, and its chemical (Hirudin) is used to dissolve unwanted blood clots.
Earthworms: (Sedentarians)
1- They eat soil extracting nutrients from it as the soil passes through the
alimentary canal.
2- They are hermaphrodites (reproduce sexually and asexually), sexually by
cross fertilizing and asexually by fragmentation followed by
regeneration.( ‫) يعني ازا قطعتها من النص بترجع بتكون حالها‬
3- See its anatomy in the figure:
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Concept 4: Ecdysozoans, from ecdysis (peeling of the skin)
Ecdysozoans shed their skin (cuticle) in a
process called molting.
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They contain eight phyla but we will only
study two of them, Nematodes and Arthropods.
Nematodes (round worms) :
 They range from 1mm to 1m in length, having a round body which has
a tip at its posterior end and blunter tip(‫)عريضة‬at its anterior end.
 Their body is covered by a tough exoskeleton called cuticle, and as it
grows it sheds off this cuticle and forms a new one.





They compose of a pseudocoelom, and it transports nutrients through
the body (because they lack a circulatory system).
They contain 25000 known species and a lot more unknown, one of
them is studied carefully and became a model in biological studies
such as aging in humans, its called C.elegans.
Nematodes are parasitic species on both animals and plants, some
are beneficial as they attack insects.
There is a nematode that attacks humans called Trichinella spiralis
which is acquired by eating undercooked meat as it contains juvenile
worms encysted in the animal meat (muscle tissue), also this
nematode develops into sexually mature worm in the humans
intestine, the females of the worm produce more juvenile worms
which travel through the body by lymphatic vessels into the muscles
where they encyst.
Some of these adapt well in the host body such as plant parasites
(they induce the plants roots to absorb more nutrients for the worm),
also the earlier mentioned nematode Trichinella spiralis regulates
some genes to make muscles more elastic to house the worm, And
gives the worm more nutrients.
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3- Arthropods (most abundant species) :
 Regulation of 2 existing hox genes led to this diversity of
arthropods.
 Arthropods are originated from Lobopods that developed through
time such as Lucigenia.
Properties of arthropods:
1- Their bodies are completely covered by a cuticle (an exoskeleton made of
chitin and layers of protein).
2- The exoskeleton is used for protection and provides attachment points for
the muscles to move the appendages (feet, mouthparts, pincer, etc)
3- In order for the arthropod o grow it has to shed its skin and produce a larger
one.
4- Arthropods have developed sensory organs such as olfactory (smell
receptor) and antennae (touching and smelling).
5- Butterflies taste food from their legs.
6- They have an open circulatory system, the heart propels the hemolymph
(instead of blood) to a space called sinuses or hemocoel  then the
hemolymph returns to the heart through pores equipped with valves
7- Although arthropods are coelomates, the main body cavity in them is the
hemocoel.
8- They exchange gasses depending on their habitat, aquatic arthropods use
gills but terrestrial ones use their specialized internal surface for gas
exchange. See figure 
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9- They are divided into three clades:
 Chelicerates.
 Myriapods.
 Pancrustaceans.
Chelicerates (spiders, scorpions,
horseshoe, ticks, mites):
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 They were named after their feeding appendages called chelicerae, and they
are divided into two main body parts: posterior abdomen and interior
cephalothorax, and most of them have simple eyes.
 The earliest members of this clade are eurypterids (water scorpions) which
can reach to 3 meters in length, and most of them are extinct.
 Some of the Chelicerates that live in the sea are sea spiders (pynogoinds)
and horseshoe crab.
 A group of modern Chelicerates are Arachnids which include spiders, mites
(parasites), ticks (blood sucking parasites) and scorpions.
 Arachnids have six pairs of appendages (one chelicerae pair for feeding and
one Pedipalps pair for sensing and defense and four pairs for walking).
 Gas exchange between hemolymph and air occurs by book lungs in spiders
stacked in the abdomen which have a large surface area.
 Many spiders have the ability to produce webs of silk (made of protein)
through specialized abdominal glands called spinnerets. They use this silk for
catching prey, escape, move, cover for eggs and mating.
Myriapods (land living species):
 They include millipedes and centipedes. And have a pair of antennae and
three pairs of appendages used for feeding including the mandibles (jaw
like appendage).
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 Millipedes (herbivorous animals): segmented worms. and each trunk
segment is formed by fusing two segments and have two pairs of legs.
 Centipedes (carnivorous animals) : each trunk segment has only one pair
of legs, they also poison the prey and paralyze it before feeding.
Pancrustaceans (paraphyletic groups
which include crustaceans and insects ) :
1- Crustaceans (crabs, lobsters and shrimps): they have many appendages
including antennae ( they are the only species that have two pairs of
antennae ) and mandibles and walking legs. They exchange gas by gills or
small cuticle but have a pair of glands to regulate salt balance.
They also have separate sexes.
Crustaceans are divided into three groups:
 Isopods : like pill bugs and wood lice
 Decapods: the cuticle is hardened by calcium carbonate ( the cover
that is on the dorsal side is called carapace). They include lobsters and
shrimps and crabs.
 Copepods : planktonic species, like shrimplike krill which grow to
about 5cm ( a major food source for humans and whales)
Other group is called barnacles (sessile species) are also among the
Crustaceans.
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2- Insects (hexapoda have six legs) : see internal anatomy 
 Most insects have flying wings that extend from the cuticle
 Many insects go through metamorphosis from larval stage (caterpillar)
into adults.
 A nymph (young insect) goes through series of molts until it reaches
the adult stage. See figure 
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 Reproduction in insects is sexual with separate sexes and fertilization
is internal. Female insects have a sac called Spermatheca to store
sperm, and its enough to lay eggs more than once ( ‫يعني الحشرات تتزوج‬
‫)مرة وحدة بحياتهاو بتضل تنزل بيض بعد هيك بدون اي عملية تزاوج‬
 Insects are classified into thirty orders.
Concept 5 : Echinoderms and Chordates are Deutereostomes
Echinoderms (slowly moving sessile marine animals):
They have a water vascular system (which is unique to them), a network of
hydraulic canals branching into tube feet that function in locomotion and
feeding.
Reproduction is sexually and they have separate sexes as they release their
gametes into water.
They include five clades:
1- Asteroidean (sea stars and sea daisies) :
Sea star have a central disk which has arms radiating from it, under these
arms are the tube feet. Under the tube feet there are flattened disks for
adhering to other molecules. see figure 
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Sea stars also use their feet to grasp the prey, then they secret their
digestive juices into the sea clamp through the stomach and begins
digesting.
Sea stars can regenerate: if they lose an arm it can regrow.
This clade also include sea daisies which absorb nutrients through a
membrane that surrounds their bodies.
2- Ophiuroidea (Brittle stars ) :
They have a central disk and long flexible arms but unlike sea stars the are
motile.
Their base lack a tube foot but secrets adhesive chemicals like sea stars.
Some of these are suspension feeders, others are scavengers.
3- Echinoidea (sea urchins and sand dollars $) :
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They have no arms but have five rows of tube feet used for slow moving.
Sea urchins have muscles that pivot their spines which help them in
protection and locomotion. They also have a mouth in the under side to
eat sea weed.
Sea urchins are spherical but sea dollars are flat disks.
4- Crinoidea (sea lilies and sea feathers) :
Sea lilies live attached to a substrate ( sessile ), but sea feathers crawl
using their long arms.
They are both suspension feeders and their mouth is upward.
5-
Holothuroidea (sea cucumbers) :
They lack spines and have a reduced endoskeleton, yet they have five
rows of tube feet around the mouth as feeding tentacles.
End of the chapter ‫الحمدهلل‬
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