Major Division in the Animal Kingdom
•
•
Phylum Ctenophora “comb jellies”
•
Similar to Cnidarians; all marine and planktonic
•
No nematocysts; some have sticky cells called colloblasts on tentacles.
•
Statocyst- sense organ for balance
•
Comb jellies have comb plates for movement- fused cilia
•
Often bioluminescent when agitated
Phylum Bryozoa “lace or “moss” animals
•
All are marine, colonial, sessile, & common
•
Small polyp- like animals; uses a lophophore or
circlet of tentacles (cilia on tentacles) for filter feeding
•
Colonies form masses that covers substrate (rock or shell)
•
Others form small stalked animals
•
Major Division in Animal Kingdom; due to Symmetry
•
Division Radiata- radial symmetry; body arranged in a circle
•
•
Good design for sessile forms that filter-feed
•
Ex: Sponges, Corals, jellyfish, Ctenophores, Bryozoans
Division Bilateria- bilaterally symmetric
•
Body arranged as mirror-halves down midline.
•
Found in all higher animal forms; an important evolutionary step.
•
Associated with cephalization (having a head) and mobility (most important)
•
Animals with bilateral symmetry usually elongate in Direction of Movement.
•
*Enigma: Bilateral symmetry is obviously a more advanced body plan than radial symmetry. Yet
both are exhibited in early Cambrian deposits (570 million years ago)
•
Embryological Cell Layers
•
Acoelomates- animals with 3 cell layers; with no coelom
–
Coelom means body cavity
Ex: Flatworms and Ribbonworms
•
Ectoderm- skin, bones, nervous tissue
•
Endoderm- digestive system, viscera
•
Mesoderm- muscles
•
Coelomates- animals with a coelom that is lined with mesoderm
–
These animals have a digestive system with 2 openings !
•
Phylum Platyhelminthes- the flatworms
•
Bilaterally symmetric; non-segmented
•
Can be marine, freshwater or parasitic
•
Two anterior nerve ganglia & two ventral nerve cords; some have eyespots
•
Incomplete digestive system (acoelomate); primitive excretory system called flame cells
•
No appendages; “like wet tissue paper”; glides across substrate on cilia that covers ventral
surface
•
Marine forms – usually small, common, live under rocks, between sand grains; some tropical
forms are brightly colored
•
3 Classes
–
Turbellaria- free living forms
•
•
Trematoda - the flukes (parasites)
–
•
Ex: Planaria (freshwater)
Ex: Liver and Blood flukes
Cestoda - tapeworms
–
Ex: Diphillobothrium latum- can get from eating raw fish
•
Phylum Nemertina (Rhynchocoela)- the ribbon worms
•
Elongated, ribbon-shaped, “noodle-like”; can break apart easily
•
Live on bottom under rocks, shells, seaweed,
•
Move by gliding on trail of slime, or by muscular contractions
•
No segments or appendages
•
Have a complete digestive system; simple circulatory system; mouth on anterior end (not midventrally as in flatworms)
•
Size ranges from few inches to several meters
•
Have long, tongue-like proboscis well suited for capturing prey, defense and for burrowing
•
Proboscis is housed in a primitive body cavity called the Rhynochocoel
•
Carnivorous – eats small worms, molluscs, and crustaceans
•
Some are very colorful; often found around coral reefs
•
Pseudocoelomate- a “false” body cavity
•
Phylum Nematoda- roundworms
10,000 species
•
Body is cylindrical; pointed at both ends; covered by a cuticle for protection; size ranges from
microscopic to 12 inches. Body form is almost identical between species.
•
Can be terrestrial, freshwater, marine, or parasitic; found in almost all environments. May be
the most abundant animal on Earth!
•
Free-living forms are important members of food web by breaking down organic detritus
(waste)
•
Pseudocoelomate- a “false” body cavity
•
Phylum Rotifer “Wheel worms”
•
Microscopic filter feeders
•
Body features:
–
Corona- twin bands of cilia; produces water current for feeding
–
Mastax- internal jaws; grinds up swallowed food
–
Retractable foot with “toes” for attachment
–
Pseudocoelomate- a “false” body cavity
•
Phylum Annelida- segmented worms
15,000 species
•
True- segmented worms; most highly developed of the worm-like invertebrates; includes the
Earthworm (Class Oligochaeta), the leeches (Class Hirudinea), and marine fanworms (Class Polychaeta)
•
Body has segments called somites; both internal and external; evolutionary significance- forms a
“hydrostatic skeleton”
•
Each segment (with a partition) can be used to change internal pressure. This results in
conservation of energy and faster motion.
•
Have a circulatory system, nervous system, and a complete digestive system (coelomate)
•
Class Polychaeta
•
(meaning many bristles) is the most commonly encountered marine worm
•
Each segment has small “bristled” appendages on each side called parapodia- which aid in
locomotion, respiration, and filter feeding
•
Some are free-swimming; most burrow or live in tubes, thus they can be called infaunal filter
feeders
•
Live in sand, mud, under seaweed & rocks; or attached to pilings
•
Morphologically Diverse! range from simple to bizarre shapes
•
This class includes: fanworms, tubeworms, lugworms, and scaleworms
•
Trochophora larva
•
Ciliated larval form-planktonic - This larval form is found in flatworms, ribbonworms, annelids
and molluscs. Because these various phyla have this larval form in their life cycles, suggest a common
ancestor