(mollusks, annelids,
arthropods, echinoderms)
I. The coelom: A major divergence in animal evolution
A. Development
of a True Coelom (Eucoelomate)
1. Has a lining of mesoderm (peritoneum)
2. Two methods of embryonic formation
a. solid
mass of mesoderm forms and splits to form two lateral coelomic
cavities (schizocoelous)
b. two
pouches (evaginations) from the gut from the mesoderm with a pair of
coelomic cavities (enterocoelous)
B. These
two methods of coelom formation = the two major lines of evolution
1. Protostome line
a. mouth--first
opening to form in the embryo
b. cells
division in a spiral pattern
c. schizocoelous
2. Deuterostome line
a. mouth--second
opening
b. anus
or terminal opening first
c. cells
division in a radial pattern
d. enterocoelous
II. Phylum Mollusca - snails, clams and their relatives
A. Protostomes
B. Soft
bodied (= mollus)
C. Shell
of calcium carbonate for protection
D. Mantle
- a tissue folded over the body to make the shell
E. Gastropods
- stomach footed
1. Diverse - found in all habitats except the air
2. Primitive forms with a twisted body so that the anus empties on
the head
3. Flattened foot
which is muscular and slimy
4. Shell usually coiled
5. A few very advanced forms--no shell as an adult, but the larvae
with shell (veliger)
6. Radula - a muscular belt-like tongue with teeth that scrape food.
F. Bivalves - two shells, one on each side
1. Foot usually a blade-like extensible structure for burrowing in
sand and mud.
2. Some (oysters and muscles) stick--hard substrates like rocks or
boats
3. Filter feeders
4. Siphons out of the mud or sand
G. Cephalopods - Ahead
foots@
1. Foot = arms or tentacles around the mouth
2. Predators - beak for biting prey
3. Mantle cavity = a contractile chamber for "jet propulsion"
4. Only mollusks with a closed circulatory system
a. constant volume
b. high pressure
c. found in high metabolism organisms
5. Well developed nervous system
1. Eyes
2. Some ability to learn
3. Complex behavior
III. Annelida - ringed worms
A. Segmented - many repeat units - some same; others modified
1. Evolutionary (specialization of parts)
2. Redundancy (serial homology)
B. Closed circulatory system
C. Organ systems well developed
D. Marine, fresh water and terrestrial
E. Example - earthworm
1. Nephridia for excretion
2. Muscles
3. Nervous system
4. Digestive system
5. Reproduction -
hermaphroditic
F. Marine worms
G. Leeches
IV. Arthropoda - jointed legs
A. Characteristics
1. Exoskeleton
a. protection
b. muscle attachments
c. restrict water loss on land
d. must shed (molt) to increase in size
2. Jointed appendages
3. Highly
specialized segments
4. Compound eyes
5. Division of labor in life cycle
6. Open circulatory system
a. larval stages ecologically different from adults
b. sometimes terminal stage for reproduction only
c. dispersal increased
B. Most successful group of organisms in the history of life on
earth (greatest number of species)
C. Chelicerata - spiders and their kin
1. Evolved in the oceans; now mostly terrestrial
a. horseshoe crabs and sea spiders
b. scorpions, spiders, ticks and mites
2. Characteristics
a. four pairs of legs
b. pedipalps for
sensation and mating
c. chelicerae - fangs with poison glands
d. two main body divisions--Cephalothorax and Abdomen
e. book gills or book lungs
D. Subphylum Mandibulata - specialized mouth parts
1. Crustacea - crabs, crayfish and relatives
a. hard, yet flexible crust (exoskeleton)
b. great variety of organisms
c. varied number of segments
d. marine, freshwater and terrestrial
2. Insecta
a. characteristics
1. 6 walking legs
2. Dorsal wings
3. Three body parts
- head, thorax and abdomen
4. Trachea
b. most numerous organisms by number of species
c. freshwater, terrestrial and aerial
d. complex life cycles
1. Gradual - young to adult
2. Nymphs
3. larva, pupa,
adult
e. pollinators
f. insects,
lice, fleas
3. Myriapods -
centipedes and millipedes
a. heads
b. trunk
of many segments each with a pair of legs
V. Deuterostome line of evolution
VI. Echinodermata - starfish and
relatives
A. Characteristics
1. Calcium skeleton in the body wall
2. Water-vascular system with tube feet
3. Decentralized nervous system
4. Radial symmetry
a. bilateral
larvae
b. adaptation
to slow movement - sessile
5. Marine only
B. Diversity
1. Starfish
2. Brittle stars
3. Sea cucumbers
4. Crinoids (sea
lilies)
WADSWORTH
Mollusca Arthropoda
8272 - 8275 9272 - 9287
Chelicerates
8277 - 8281 9290 - 9298
Mandibulates
8283 - foot 9330 - 9334
9200 - 9202 9359 - 9362
9215 - 9223 Echinoderamata
Annelida 9389 - 9404
9224 - 9230 9408*
9257 - 9261