Animals III: Mollusca, Arthropoda, & Echinodermata

Phylum Echinodermata


Embryonic Development: Triploblastic Eucoelomate Deuterostome

Circulatory: 3 systems: reduced open hemal (around gut), ciliated eucoelom (for gas exchange via gills), and ciliated hydrocoel (for gas exchange via tube feet)

Digestive: Complete

Nervous: Nerve ring

Symmetry: Pentamerous radial

Special Features: Calcareous endoskeleton, tube feet & pedicellaria, hydrostatic skeleton and water vascular system with madreporite

Classes:
 * Echinoidea sea urchins
 * Asteroidea starfish
 * Holothuroidea sea cucumbers
 * Ophiuroidea brittle stars





Phylum Mollusca


Embryonic Development: Triploblastic Eucoelomate Protostome

Circulatory: Open (except for cephalopods which have closed circulatory systems); gills

Digestive: Complete

Nervous: Most have localized ganglia and a pair of nerve cords along with statocysts (balance organs).

Clade: Lophotrocazoa

Symmetry: Bilateral with cephalization

Special Features: Visceral mass, radula, mantle (which secretes shell), muscular foot, torsion (gastropods)

Classes:
 * ​Polyplacophora chitons
 * Bivalvia clams, mussels, oysters
 * Gastropoda snails, slugs, abalone
 * Cephalopoda octopus, squid

Phyla Arthropoda (Marine)
Also see: Terrestrial Arthopods

Embryonic Development: Triploblastic eucoelomate protostome

Circulatory: Open

Digestive: Complete

Symmetry: Bilateral with cephalization

Special Features: Segmentation, chitonous exoskeleton, jointed appendages

Classes:
 * ​Crustacea lobsters, crab, crayfish, pillbugs
 * Arachnida spiders, scorpions, mites
 * Myripoda centipedes, millipedes
 * Insecta Insects