Echinoderms and Molluscs

Echinoderms and Molluscs

Phylum Echinodermata

Includes sea stars, brittle stars, sand dollars, sea urchins, & sea cucumbers

• Start life as bilateral, free-swimming larva and change to sessile or sedentary adult

• Adults have radial symmetry • Have a true coelom (body cavity)• Capable of extensive regeneration • Have a nervous system but no head or brain

in adults

Phylum Echinodermata

• No circulatory, respiratory, or excretory systems • Tube feet on the underside of arms help in moving &

feeding • One-way digestive system consists of mouth with

oral spines, gut, & anus • Separate sexes • Reproduce sexually & asexually • Includes 5 classes:

          * Crinoidea - sea lilies & feather stars          * Asteriodea – sea stars          * Ophiuroidea - basket stars & brittle stars          * Echinoidea - sea urchins & sand dollars          * Holothuroidea - sea cucumbers

Phylum Mollusca• have a true coelom (body cavity)

Similar larval stage as Echinoderms• Bilateral Symmetry

• Characteristics of Mollusks· Visceral Mass (organs)· Foot (muscle, movement)· Shell in most· Radula - tongue-like structure, sharp· Gills for respiration· Most have separate sexes

• Types of Mollusks· Gastropods - snails, slugs, nudibranchs ("stomach foot")· Bivalves - clams, oysters ("two doors")· Cephalopods - nautilus, cuttlefish, squid, octopus ("head foot")