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Chapter 11
Organ grade level or organization and complexity. No true systems (digestive tract has
some specialized organs but is overall very simple).
Phylum Platyhelminthes
General Characteristics
1) Triploblastic (applies all three phyla of acoelomates).
2) Bilateral symmetry (applies all three).
3) Body is flattened dorsoventrally (compressed dorsoventrally).
4) Ectoderm is very specialized w/ distinct epidermis in all three phyla. *Note:
specialized "flatworm" characteristics associated externally w/ epidermis.
a) some spp. epidermis is syncitial
1) Having one/few epidermal cells having many nucleus. Usually elaborating cilia in
many spp. Aid in locomotion and protection.
b) rhabdites - specialized epidermal cells and extracellular structures of many flukes,
which aid in locomotion.
c) Syncytial tegument - extraepidermal layer of one/few multinucleated cell(s) w/
protective covering. In many flukes.
d) Same cellular extraepidermal structures and epidermis. One nucleus/cell. Multicellular
arrangement of epidermis and sometimes ciliated structures.
5) Muscular development and arrangement into simple body wall muscles used mainly
for locomotion.
6) No body cavity (acoelomate).
7) Digestive tract is incomplete:
a) No mouth (oral opening directly into pharynx).
b) No true stomach structure (pharynx opens into a complex "intestinal" structure). In
some spp. there is no intestinal structure but rather GVC-like cavity. No
contact w/ mesoderm.
c) In tapeworms, there is no digestive tract; absorption of nutrients is direct through skin
(epidermis) and/or through oral opening. Direct absorption of soluble
nutrients by cells and tissues.
8) Simple arrangement of nerve cells and sensory organs (EX: eyespots of planaria).
9) Sense organs
10) Excretion - mostly passive diffusion of soluble wastes; some specialized cells and
organs protonephridia cells (("primitive excretory cells") (flame cells)) make
up simple excretory organs
11) Respiration (gas exchange by simple diffusion) no circulatory system therefore
intercellular diffusion and transport from cell to cell.
12) Reproduction
a) Sexual : monoecious spp.
b) Asexual : regeneration and fission
13) Range from free-living planaria to parasitic flukes and tapeworms.
Classification
Class Turbellaria - common name planaria - scientific name Dugesia sp.
1) Free-living
2) Mostly freshwater spp.
Class Monogenea
1) Mostly parasites of fish in skin/gills.
2) Free-living larval stages
3) Ciliated, mobile larvae
4) Some parasitic flukes in class
Class Trematoda - genus Fasciola spp. - Clonorchis spp.
1) Major parasitic flukes
2) Includes blood flukes and liver flukes.
Class Cestoda - tapeworms - Taenia spp. - pork tapeworm
1) All spp. are parasitic, which lack any type of digestive tract.
Class Turbellaria
1) Range from roughly 5 mm -> 50 cm
2) Usually covered w/ ciliated epidermis - cilia used mostly for locomotion; cilia
sometimes used to create water currents to draw water and food materials near
pharynx and into digestive tract.
Form and Function of planaria
External
a) Ciliated epidermis - specialized rhabdites, rod shaped wells of epidermis. Rhabdites
water- filled; Can discharge a release of water and a protective mucous
sheath around body of organism (mucous layer is composed of complex
polysaccharides). Carbohydrate polymers, simple and complex saccharides (sugars)
monosaccharides monomeric simple sugars. Glucose (C6H1206 or CH20) general
formula for carbs.
1) glucose - used for two types of metabolic processes
a) Catabolism : glucose breakdown (enzymatically) to yield energy in form of ATP.
b) Anabolism: biosynthesis; "building" complex organic molecules (enzymatically) from
simple starting materials such as glucose, e.g. glucose polymerize, complex
saccharides such as:
plants 1) starch : energy storage form of example.
animals 2) cellulose : structural polysaccharide of glucose
animals 3) glycogen : energy storage form of glucose
4) chitin : structural form of glucosamine
5) mucosal polysaccharide : complex forms of glucose and many other carbohydrates to
make mucous layers and/or structures.
2) Polysaccharide materials
a) protection
b) prevents desiccation (water loss under adverse conditions)
c) facilitate locomotion
d) capture food particles
Internal
Complex arrangement of body muscles attached to endodermal, mesodermal, and
ectodermal material, allowing contortion of body in several different planes
relative the longitudinal, central axis thus allow facilitation of locomotion. "Swimming"
mobility - collective use of cilia, muscles, mucous layer for locomotion.
Muscle fibers arranged circularly, laterally, and longitudinally.
Nutrition and Digestion : digestive tract is incomplete
1) "mouth" : oral opening (very simple and unspecialized) - simply an opening through
which pharynx (pharyngeal sheath) can be extended.
2) Pharynx : pharyngeal sheath. Opens externally toward posterior region of organism
and can be extended through oral opening; connects internally, directly to
intestines.
3) Intestines : major digestive and adsorptive region of digestive tract; very highly
branched and extends throughout bulk of interior of body. Aids in intercellular
transport (directly) of nutrients to other cells and tissues of body (active transport and
passive diffusion of partially metabolized structure). The inside (lumen) of
intestines is highly folded (convoluted) to provide greater surface area for more efficient
adsorption of nutrients w/in intestines.
4) Digestion of food particles is extracellular by digestive enzymes secreted by
specialized cells of intestinal lumen.
a) Complex food macromolecules such as polysaccharides, proteins, and fats are
extracellularly digested into their constituent numeric subunits:
polysaccharides ----------------->monosaccharide---------------->intercellular transported to
cells and tissues
starch & glycogen digestion glucose absorption
proteins---------------->amino acids-------------->transport catabolism and some anabolism
protease absorption
fats and fatty acids-------------------------->glucose------------->used for catabolism and
anabolism
directly metabolized
Digested materials (simple monomers)-->absorbed by convoluted lumen of intestine and
passed directly (intercellular transport) to cells that require specific
nutrients. Further metabolism of simple monomers occurs intracellularly.
Excretion and Osmoregulation
Removal insoluble wastes (for example cellulose) no external structure for removal of
wastes.
Removal soluble wastes: ionic forms of materials, toxic waste products
Protonephridis- simple, primitive organ-like structures which remove ions and control
osmotic pressure of cells of organism and constitute tissues (similar to role
of contractile vacuole of protozoa). Unicellular "animals".
Chapter 12
Structure
1) Body cavity designated as pseudocoel.
2) Simple arrangement of tissues and organs within pseudocoelomic cavity.
3) Triploblastic: three germ layers.
4) Ectoderm basically same as in all three, giving rise to epidermis (some specialized
structures present).
5) Endoderm basically same all three digestive system on tract derived from endoderm.
Key Differences
1) Complexity, arrangement, and function of mesoderm.
a) Acoelomates: mesoderm is in "continuous" contact with endoderm and ectoderm;
specific interaction with digestive portion of organism: NO BODY CAVITY.
b) Pseudocoelomates: mesoderm "discontinuous" with regard to endoderm but not
contact with ectoderm.
c) Coelomate: also called eucoelomate; body cavity derived and embedded within
mesoderm itself; mesoderm is complex and very specialized with two specific
tissues derived form mesodermal germ layer.
1) Mesentary: mesodermal tissue specialized for suspending and attaching to specific
digestive system organs; divides eucoelom into distinct chambers throughout
body, giving rise to internal segmentation (even early embryonic stage) and external
segmentation. Internal segmentation is primarily due to lateral partitioning by
mesentary; some longitudinal partitioning occurs within eucoelomate by longitudinal
arrangement of mesentary tissue.
2) Peritoneum: internal, mesodermal lining of eucoelom.
Functional Aspects
1) Pseudocoelom: provides anchor matrix of muscle fibers, etc., derived form mesoderm
for suspension of digestive system; fluid-filled cavity, therefore
hydrostatic pressure provides support for overall body structure and shape of organism;
mostly only mesodermally. Derived, longitudinal muscles for longitudinal
coiling of organisms (roundworms of Phylum Nematoda).
2) Eucoelom: very good anchoring and suspension internal organs by mesentary,
providing support, circulation is crude, open circulatory system of arthropods,
excretion and osmoregulation (some spp.), respiration (gas exchange) in some aquatic
spp. No digestion occurs within eucolom; only occurs within digestive
system suspended within eucoelom.
Pseudocoelomate Phyla:
1) Phylum Rotifera (rotifers) - small, microscopic multicellular aquatic.
2) Phylum Nematoda (roundworms) - common organisms. vinegar eels & nematodes.
3) Phylum Entoprocta - many microscopic hydra-like pseudocoelomates. lots specialized
internal structure, especially within eocoelom. mostly marine organisms.
Phylum Rotifera - having, bearing roti = wheel
External structures
Organisms bearing some type of specialized structure: corona (anterior, wheel-like
structure with many cilia for locomotion and feeding. Also close to mouth.
Internal structures
1) Digestive system is complete with mouth associated with a specialized external
structure (corona). pharynx is connecting mouth to digestive region and also with
gastric gland (stomach-like organ which secretes acids and enzymes for chemical and
enzymatic digestion of food particles). Intestine and anus present.
Chapter 13
Phylum Mollusca - means soft
1) True coelomic animals
2) Belong protostomates have blastopore
3) All organ systems present and well-developed
4) Tcochophore larva: Free-swimming ciliated marine larva
Biological Contributions
1) Radula---> rasping organ
2) Respiratory organs (lungs, gills) gas exchange.
3) Mantle: secretes shell or can be modified for different uses.
4) Open circulatory system: heart, vessels, blood sinuses.
5) Some of largest invertebrates due to respiratory system and coelomic cavity.
6) Foot: muscular organ used primarily in locomotion.
7) "Skin" eye: highly developed comergent with "brain" eye.
8) Terrestrial and aquatic - marine\freshwater
9) Secondary cavity within mesoderm
10) Mesodermal epithelium parietal to peritoneum.
11) Mesentary continuous of peritoneum.
12) Organs covered in visceral peritoneum
13) No crowding. Stable arrangement
14) Coelomic fluid usually ciliated lining through aids in movement in wastes and food.
15) Parity also acts as hydrostatic skeleton; variety of movements can be produced via
contraction of muscles.
16) All higher vertebrates and invertebrates have coelom.
17) Molluscs don't seem to really take advantage of it; theirs is limited to a space around
heart. Sometimes gonads and part of kidney.
Characteristics of Molluscs
1) Bilateral symmetry (some bilateral asymmetry) and usually with a definite head.
2) Ventral body wall is specialized as muscular foot; mainly for locomotion
3) Dorsal body wall forms a pair of folds (mantle); secretes shell (absent in some)
modified into gills or lungs. Mantle is ectodermal\coelomic cavity mesodermal.
4) Surface epithelium usually ciliated with mucous glands and sensory nerve endings.
Secreted mucous aids locomotion; forms "slime trait" in some.
5) Coelom limited to area around heart, perhaps lumen of gonads or kidneys.
6) Anus usually empties into mantle cavity. Complex digestive system : radula.
7) Open circulatory system (mostly closed in cephalopods) usually three chambered
heart, blood vessels, sinuses, blood pigments.
8) Gaseous exchange in lungs, gills, mantle, or body surface.
9) One or two metanephridia (kidneys) emptying into mantle cavity. Tubular, tissue
structure physically removing wastes.
10) Nervous system of pairs; cerebral, pleural, pedal, and visceral ganglia. Nerve cords,
subepidermal plexus, ganglia are centralized in nerve ring in gastropods
and cephalopods.
11) Sensory organs of touch, taste, smell, equilibrium and vision ("skin" eye); eyes highly
developed in cephalopods.
Chapter 14
Phylum: Annelida = "little ring"
I. Characteristics
A. Segmented body with bilateral symmetry.
1. Segments arranged in linear series and externally marked by circular grooves called
annuli.
2. Body segmentation is known as metamerism, and is internal as well as external.
B. Body wall with outer circular and inner longitudinal muscle layers; outer transparent
moist cuticle secreted by epithelium.
C. Chitinous setae often present; exception = leeches.
D. A true coelom which is divided by the septa; exception = leeches.
E. Closed circulatory system and segmentally arranged; respiratory pigments such as
hemoglobin, hemerythrin, and chlorocruorin often present; amoebocytes in
blood plasma.
F. Complete digestive system which is not metamerically arranged.
G. Respiration through skin, gills, or parapodia. Parapodia are paired lateral processes on
each side of most segments in polychaete annelids; variously
modified for locomotion, respiration, or feeding.
H. Excretory system typically a pair of nephridia for each metamere. Nephridia are
segmentally arranged, paired excretory tubules of many invertebrates,
notably the annelids. In a broad sense, any tubule specialized for excretion and/or
osmoregulation; with an external opening and with or without an internal
opening.
I. Nervous system with a double ventral nerve cord and a pair of ganglia with lateral
nerves in each metamere; brain a pair of dorsal cerebral ganglia with
connectives to cord.
J. Sensory system of tactile organs, taste buds, statocysts (in some), photoreceptor cells,
and eyes with lenses (in some).
K. Hermaphroditic; larvae, if present, are trochophore type; asexual reproduction by
budding in some; spiral and mosaic cleavage.
II. Body Plan
A. Prostomium: anterior "segment" which houses the head.
B. Pygidium: posterior terminal "segment" holding the anus.
C. Coelom develops embryonically as a split in the mesoderm on each side of the gut
(schizocoel).
1. This forms a pair of coelomic compartments in each segment.
2. Each compartment is surrounded with a peritoneum (layer of medodermal epithelium).
a) This peritoneum forms dorsal and ventral mesenteries.
b) Septa are formed where the peritonea of adjacent segments meet.
3. Coelom is filled with fluid and serves as a hydrostatic skeleton.
III. Classification
A) Class Polychaeta = "many long hairs"
1) Largest and most primitive: more that 5300 species, mostly marine.
2) Size: 5 to 10 cm, although some less than 1 mm and long as 3m.
3) Live under rocks, in coral crevices, abandoned shells, or burrow into the sand or mud;
some adopt tubes of other animals; some pelagic.
4) Form and Function
a) Different from other annelids in well-differentiated head with specialized sense organs,
paired parapodia, and no clitellum.
b) Many setae, usually arranged in bundles on parapodia.
c) No permanent sex organs, hermaphroditic, metamorphosis involving trochophore
larva.
d) Tube dwelling polychaetes secrete many types of tubes
1) Parchmentlike (14-5 pg. 300)
2) Calcareous (14-3a pg. 299)
3) Sand, seaweed, etc. cemented by mucous secretions.
4) Line burrows with mucous (14-7 pg. 301)
e) Has a true head, or prostomium.
f) Sense organs are highly developed and include eyes, nuchal organs, and statocysts.
g) Reproduction
1) Gonads appear as temporary swellings of the peritoneum and shed their gametes into
the coelom.
2) They are carried outside through gonoducts, through nephridia, or by rupture of the
body wall.
3) Fertilization is external.
5) Genus: Nereis - the clam worms
a) errant polychaetes that live in mucus-lined burrows in or near low tide.
b) grow 30 to 40 cm in length
c) prostomium bears a pair of stubby palps (touch and taste), a pair of short sensory
tentacles, and two pairs of small dorsal eyes that are light sensitive
d) peristomium bears the ventral mouth, pair of chitinous jaws, and four pairs of sensory
tentacles.
e) parapodium formed of two lobes: a dorsal notopodium and a ventral neuropodium.
1) these lobes are supported by one or more chitinous spines (acicula).
f) feeds on small animals, other worms, larval forms
B. Class Oligochaeta = "few long hairs"
1) Setae may be long/short, straight/curved, blunt/needlelike, single/in bundles although
less setae than in Polychaeta (hence the name)
2) Earthworms ("night crawlers")
a) "typical earthworm" is 12 to 30 cm long although giant tropical earthworms may have
from 150 to 250 or more segments and grow to as much as 4m in length.
b) Form and Function
1) mouth is overhung by a fleshy prostomium at the anterior end
2) in most, each segment bears four pairs of chitinous setae though some may have up to
100 or more per segment
3) seta is a bristlelike rod set in a sac within the body wall and moved by tiny muscles.
they project through small pores in the cuticle.
4) peristaltic movement: contractions of circular muscles in the anterior end lengthen the
body, pushing the anterior end forward where it is anchored by setae;
contractions of longitudinal muscles then shorten the body, pulling the posterior end
forward.
c) Nutrition
1) scavengers feeding mainly on decayed organic matter
2) food is moistened by secretions from the mouth, then drawn in by sucking action of
the muscular pharynx
3) calciferous glands along the esophagus secrete calcium ions into the gut and so reduce
the calcium ion concentration formed by the calcium in the soil - they
also regulate pH of the body
4) after esophagus, food is stored temporarily in the thin-walled crop before being passed
on into the gizzard, which grinds the food into small pieces
5) digestion and absorption take place in the intestine with the aid of intestinal folds
known as typhlosoles
6) chlorogogue tissue surrounds the intestine and dorsal vessel and serves as a center for
the synthesis of glycogen and fat (equivalent of liver cells)
7) when ripe, the chlorogogue cells are released into the coelom where they float free as
cells called eleocytes which transport materials to body tissues
8) chlorogogue cells can pass through segments, and are often found in places of damage
d) Circulation and Respiration
1) double transport system: coelomic fluid and circulatory system carry food, wastes, and
respiratory gases
2) blood is carried in a closed system of blood vessels, including capillary systems in the
tissues and five main blood trunks (aortic arches) running lengthwise
through the body
e) Excretion
1) a pair of metanephridia, the organs of excretion, is found in each somite except the
first three and the last one
2) each nephridium occupies parts of two successive somites
3) nephrostome, a ciliated funnel, lies just anterior to intersegmental septum and leads by
a small ciliated tubule through the septum into the somite behind, where
it connects with the main part of nephridium
4) this part of nephridium is made up of complex loops of increasing size, terminating in
bladderlike structure leading to nephridiopore which opens to the outside
to release the waste
f) Nervous system and sense organs
1) CNS made of pair of cerebral ganglia(brain) above the pharynx and a pair of
connectives passing around the pharynx connecting the brain with the first pair of
ganglia in the nervecord
2) each pair of fused ganglia gives off nerves to the body structures, which contain both
sensory and motor fibers
3) neurosecretory cells for endocrine function are found in the brain and ganglia
4) for rapid escape movements most annelids are provided with several giant axons or
giant fibers located in the ventral nerve cord - this large diameter increases
the rate of conduction and makes possible simultaneous contractions of muscles in many
segments
5) many small sense organs; no eyes but many lens-shaped photoreceptors in the
epidermis; mostly negatively phototactic to strong light and positively phototactic
to weak light
g) Reproduction and development
1) monoecious
2) two pairs of small testes and two pairs of sperm funnels are surrounded by three pairs
of large seminal vesicles
3) eggs discharged by ovaries in coelomic cavity where they are carried by oviducts to
the outside through female genital pores
h) primary representative is Lumbricus sp., which is used for study in most classrooms
3. Freshwater oligochaetes
a) usually smaller and have more conspicuous setae than earthworms
b) more mobile and better developed sense organs
c) generally benthic forms that creep about on bottom or burrow in the soft mud
C. Class Hirudinea = "characterized by leech"
1) predominately freshwater although some marine and few terrestrial
2) most between 2 and 6 cm, but the largest is 30 cm
3) hermaphroditic
4) lost setae in exchange for suckers for attachment while sucking blood
5) gut specialized for storage of large quantities of blood
6) Form and Function
a) fixed # of somites (usually 34 although 17 or 31 in some groups) although they appear
to have more because each somite is marked by transverse grooves to
form from two to 16 superficial rings or annuli.
b) leeches lack distinct coelomic compartments and coelom is filled with connective
tissue and system of spaces called lacunae.
c) movement by looping movements of body, by attaching first one sucker and then the
other and pulling up the body
d) aquatic leaches swim with graceful undulatory movement
7) Nutrition
a) predaceous
b) fluid feeders which prefer to feed on tissue fluids and blood pumped from wounds
already open
c) some have cutting plates or "jaws"
8) Respiration and excretion
a) gas exchange through skin except in some fish leeches which have gills
b) 10 to 17 pairs of nephridia for excretion
9) Nervous and sensory systems
a) 2 brains - one in head and composed of six pairs of fused ganglia forming a ring
around the pharynx, and the other in the tail composed of seven pairs of fused
ganglia
10) Reproduction
a) hermaphroditic but practice cross-fertilization in copulation
11) Circulation
a) some retain oligochaetic circulation
b) in others, no traditional vessels but the coelomic sinuses form the system is which
blood is propelled by contractions of certain longitudinal channels
Chapter 15
Phylum Arthropoda
This is the most extensive phylum in the animal kingdom. It is composed of 3/4 of all
known species. Approximately 900,000 species of arthropods have been
recorded. Included are spiders, scorpions, ticks, mites crustaceans, millipedes, centipedes,
insects, and some others. There is an extended fossil record.
Arthropods are eucoelomate protostomes with well-developed organ systems. Most
species have combined or fused somites and appendages into functional
groups called tagmata for specialized purposes.
Although all types - carnivorous, omnivorous, and symbiotic - occur, the majority are
herbivorous. In diversity of ecological distribution, the arthropods have no
rivals.
Characteristics
1) Bilateral symmetry; metameric body divided into tagmata consisting of head and
trunk.
2) Jointed appendages; primitive, one pair to each somite. Often modified for specialized
functions.
3) Exoskeleton of cuticle (protective noncellular organic layer secreted by external
epithelium) containing protein, lipid, chitin, and often calcium carbonate
secreted by underlying epidermis and shed (molted) at intervals.
4) Complex muscular system with exoskeleton for attachment, striated muscles for rapid
actions, smooth muscles for visceral organs; no cilia.
5) Reduced coelom in adult; most of body cavity consisting of hemocoel (sinuses in
tissues) filled with blood.
6) Complete digestive system; mouthparts modified form appendages and adapted for
different methods of feeding.
7) Open circulatory system with dorsal contractile heart, arteries, and hemocoel.
8) Respiration by body surface, gills, tracheae (air tubes), or book lungs.
9) Paired excretory glands called coxal, antennal, or maxillary glands present in some,
homologous to metameric nephridial system of annelids; some with other
excretory organs (malpighian tubules).
10) Nervous system w/ dorsal brain connected by a ring around gullet to a double nerve
chain of ventral ganglia; fusion of ganglia in some species; well-developed
sensory organs.
11) Sexes usually separate, with paired reproductive organs and ducts; usually internal
fertilization; oviparous of ovoviviparous; often metamorphosis;
parthenogenesis in few forms.
Similarities between Arthropoda and Annelida
1) External segmentation
2) Segmental arrangement of muscles
3) Ventral nerve cord w/ metamerically arranged ganglia and dorsal cerebral ganglia
4) Spiral cleavage (found in some arthropods)
Differences between Arthropoda and Annelida
1) Fixed number of segments (in adults)
2) Usually lack intersegmental septa
3) Pronounced tagmatization (compared w/ limited tagmatization in annelids)
4) Coelomic cavity reduced; main body cavity a hemocoel
5) Open circulatory system
6) Special mechanisms (gills, tracheae, book lungs) for respiration
7) Exoskeleton containing chitin
8) Jointed appendages
9) Compound eyes (also present in a few annelids) and other well-developed sense
organs
10) Absence of cilia
11) Metamorphosis in many cases
Arthropods are very successful:
1) versatile exoskeleton
a) cuticle : outer covering secreted by underlying epidermis.
1) endocuticle : inner, thicker cuticle. contains chitin bound w/ protein. this makes it
flexible and lightweight, while still protective.
2) epicuticle : outer, thinner cuticle. composed protein and lipid. Protein is stabilized and
hardened by tanning, adding further protection.
Both are composed of several layers.
May be soft and permeable or may form a veritable coat of armor. Between body
segments and between segments of appendages it is thin and flexible, creating
movable joints and permitting free movements. It may also line foregut and hindgut, line
and support trachea, and be adapted for biting mouthparts, sensory
organs, copulatory organs, and ornamental purposes.
It does, however, impose important restrictions on growth. To grow, an arthropod must
shed its outer covering at intervals and grow a larger one - called ecdysis
or molting. Weight limits ultimate body size.
2) Segmentation and appendages more efficient locomotion.
a) Somites provided w/ pair appendages
1) Arrangement modified: segments and appendages specialized for adaptive functions.
EX: limb segments essentially hollow levers moved by internal muscles.
Jointed appendages equip w/ sensory hairs and also been adapted for sensory functions,
food handling, swift and efficient walking legs, and swimming appendages
3) Air goes directly to cells.
a) Highly efficient tracheal system of air tubes. Deliver oxygen directly to tissues and
cells and makes high metabolic rate possible. Also helps limit body size
b) Aquatic breathe through some form gill also quite efficient
4) Highly developed sense organs
a) Have great variety. Range from compound (mosaic) eye to simpler senses of touch,
smell, hearing, balancing, chemical reception, and so on.
5) Complex behavior patterns
a) Exceed most other inverts in complexity and organization of their activities. Innate
(unlearned) behavior unquestionably controls much of what they do, but
learning also plays an important part in most of them
6) Reduced competition through metamorphosis
a) Many arthropods pass through metamorphic changes, including larval form quite
different from adult in structure. Larval form often adapted for eating different
kind of food from that of adult. Therefore less competition w/in species.
Subphylum Trilobita
Believed to have beginnings before Cambrian period, in which they flourished. All
species in this subphylum has been extinct about 200 million years.
Subphylum Chelicerata
The chelicerate arthropods are an ancient group that includes eurypterides, horseshoe
crabs, spiders, ticks and mites, scorpions, and sea spiders. Characterized
by having paired appendages that include a pair of chelicerae, pair pedipalps, and four
pairs of walking legs (except horseshoe crabs). Most chelicerates suck up
liquid food from their prey.
Class Merostomata
Subclass Eurypterida
a) All Eurypterids are now extinct. They are considered ancestors of horseshoe crab and
scorpion, which accounts for their common name giant water scorpion.
Subclass Xiphosurida - horseshoe crabs
Only five species survive today. Found in all oceans, but most abundant in polar waters.
Structure
a) Unsegmented, horseshoe-shaped carapace (hard dorsal shield)
b) broad abdomen w/ long telson (tailpiece)
1) six pairs broad, thin appendages fused in median line
c) Cephalothorax bears five pairs of walking legs and pair chelicerae
d) Book gills (flat leaflike gills) are exposed on some abdomen appendages
e) Two compound and two simple eyes on carapace.
Swim by means of abdominal plates and can walk with its walking legs. Feeds on worms
and small molluscs at night. It seizes w/ chelicerae.
Class Pycnyogonida - sea spiders
Characteristics
1) Range from few millimeters long and larger.
2) Small, thin bodies and usually four pairs long, thin walking legs.
UNIQUE 3) Somites can be reduplicated.
4) Subsidiary pair of legs (ovigers) in males, used to carry developing eggs.
5) Equipped w/ chelicerae and palps.
Structure
1) Mouth located tip long suctorial proboscis used to suck juices from soft-bodied
animals.
a) Tubular sucking or feeding organ w/ mouth at end.
2) Most have four simple eyes
3) Circulatory system is limited to simple dorsal heart
4) Excretory and respiratory systems are absent
5) Long, thin body and legs provide large surface in proportion to volume, that is
sufficient for diffusion of gases and wastes.
6) Due small size, digestive system extends into legs and most gonads are found there.
Class Arachnida
This class not only includes spiders, but also scorpions, pseudoscorpions, whip scorpions,
ticks, mites, daddy longlegs (harvestmen), and others. The differences
lie in form and appendages. Mostly free living and more common in warm, dry regions
than elsewhere.
Arachnid tagmata are a cephalothorax and abdomen. The cephalothorax usually bear pair
chelicerae, pair pedipalps, and four pairs walking legs. Antennae and
mandibles are lacking. Most arachnids are predaceous and may be provided w/ claws,
fangs, poison glands, or stingers. Usually have sucking mouthparts or
strong sucking pharynx.
Some species of arachnids are dangerous, but most are harmless to humans.
Order Araneae - Latin for spider
Large group of 35,000 species distributed all over the world.
Body structure
1) Cephalothorax (prosoma) - fused head and thorax of arthropod
2) Abdomen (opisthosoma)
Both unsegmented and joined by slender pedicel
3) Chelicerae - anterior appendages in pair
a) fangs have poison glands
4) Pedipalps - second pair appendages that contain basal parts with which they chew
5) Four pairs walking legs terminate in claws.
6) Simple eyes contain lens, optic rods, and retina
a) Used chiefly for perception of moving objects, but some actually see images.
7) Sensory setae
a) All used to communicate some information about environment.
Feeding habits
All predaceous, largely feed on insects. Quickly kill prey with fangs and poison. They
chase prey, ambush them, or trap them in a net of silk. Unique adaptation of
spinning glands. After prey is seized with chelicerae and venom injected, tissues liquefied
with digestive fluid and sucked up. Spiders with teeth at bases of
chelicerae crush or chew up prey, aiding digestion by enzymes from mouth.
Respiration
Breathe by means book lungs or tracheae or both. Book lungs are unique to spiders,
consisting of many parallel air pockets extending into a blood-filled chamber.
Air enters chamber by slit in body wall. Tracheae make up system of air tubes that carry
air directly to tissues form openings called spiracles.
Excretion
Unique excretory system of malpighian tubules, which work with specialized rectal
glands. Potassium and other solutes and waste materials are secreted into
tubules, which drain fluid into intestine. Rectal glands reabsorb most of potassium and
water, leaving behind such wastes as uric acid. Many spiders have coxal
glands - modified nephridia which open at coxa , or base, of first and third walking legs.
Web-spinning
Important factor in lives of spiders. Two or three pairs spinnerets containing hundreds of
microscopic tubes run to special abdominal silk glands. A scleroprotein
secretion emitted as a liquid apparently hardens as a result of being pulled from
spinnerets and forms a silk thread. Stronger than steel threads of same diameter.
Believed to be second only in strength to fused quartz fibers.
Web used for trapping insects is the most familiar, but varies with different species.
Also other uses. Line nests; form sperm webs or egg sacs; build draglines; make bridge
lines, warning threads, molting threads, attachment discs, or nursery webs;
or wrap up prey securely. Not all spiders use webs either. Wolf spiders, jumping spiders,
and fisher spiders simply chase and catch their prey.
Reproduction
Male spins small web, deposits a drop of sperm on it, and then picks sperm up and stores
it in the special cavities of his pedipalps. When he mates, he inserts
pedipalps into female genital opening to store sperm in his mate's seminal receptacles.
Usually a courtship ritual before mating. The female lays her eggs in a silken
net, which she may carry about or may attach to a web or plant. A cocoon may contain
hundreds of eggs, which hatch in approximately 2 weeks. Young usually
remain in egg sac for a few weeks and molt once before leaving it. Several molts occur
before adulthood.
Dangerous Spiders
a) Black widow - Latrodectus mactans - venom neurotoxic.
1) Small to moderate in size
2) Shiny black w/ bright orange or red "hourglass" on underside of abdomen
b) Brown recluse - Loxosceles reclusa - venom hemolytic.
1) Smaller than black widow
2) Brown w/ violin-shaped dorsal stripe on its back
Order Scorpionida - scorpions
Found mostly in tropical and subtropical regions. They are secretive, hide in burrows,
under objects, and feed at night.
Structure
1) Short cephalothorax, bearing appendages.
a) Small, three jointed chelicerae
b) Large, six jointed chelate (pincerlike) pedipalps
2) Pair of large median eyes and two to five pairs of small lateral eyes.
3) Preabdomen has seven segments
4) Postabdomen, or tail, has five segments
a) End has stinging apparatus: bulbous base and curved barb injects venom
5) On ventral side of abdomen are comblike pectines - tactile organs used for exploring
ground or in sex recognition
Reproduction
1) Perform complex mating dance.
a) Male deposits a spermatophore and female takes it into her orifice.
2) Either ovoviviparous or viviparous
Order Opiliones: harvestmen
More of a scavenger than regular spiders. Often called daddy longlegs
Structure
1) Abdomen and cephalothorax are broadly joined, without constriction of pedicel.
2) Abdomen shows external segmentation
3) Four pairs of long, spindly legs
4) End of chelicerae are pincerlike
Order Acari: ticks and mites
Many acarines are parasitic during one or more stages of their life cycle. Most medically
and economically important group of arachnids. Spider mites are serious
agricultural pests on many plants. Chiggers cause an irritating dermatitis and some also
transmit Asiatic scrub typhus. Other species cause mange in domestic
animals. There are additionally ticks which transmit disease, such as Rocky Mountain
spotted fever, and cattle ticks.
Structure
1) Complete fusion of cephalothorax and abdomen
2) No external division or segmentation
3) Mouthparts on anterior projection are called capitulum
4) A chelicerae can be found on both sides of the mouth
5) Ventral bases of pedipalps are fused to form hypostome
6) Rostrum or tectum - snoutlike projection on the head- extends dorsally over the mouth
7) Four pairs of legs
Reproduction
1) Sperm transferred directly
2) Most species transfer sperm indirectly by spermatophore
Mite structure
1) Long, hairlike setae on legs for swimming (aquatic forms)
2) Convex dorsal surface
More Notes