echinoderm

a member of phylum Echinodermata

Classifying Echinoderms

can be found in all ocean zones; have three germ layers; have radial symmetry; most also have an endoskeleton made of ossicles

water-vascular system

a system of canals and tubes within echinoderms that are used for circulating nutrients, moving, and capturing food

tube foot

a small, soft, tubular structure in echinoderms used for locomotion and food capture; part of the water-vascular system

Echinoderm Structure

they breathe through their tube feet or gills; have a closed digestive system; have a nerve net like cnidarian that enables them to sense and respond to their environment; have an open circulatory system; some can regrow a lost limb

Brittle Stars

class Ophiuroidea; look like starfish but have long, thin arms; readily discard their arms when attacked/disturbed, and then regenerate them

Sea Stars

class Asteroidea; most familiar echinoderms; variety of colors; various numbers of arms

Sea Lilies

class Crinoidea; sessile; look more like plants; found as fossils

Sea cucumber

class Holothuroidea; live in shallow tropical seas; widely distributed throughout the world's oceans; lack ossicles

Sea Urchins

class Echinoidea; like marine porcupines or hedgehogs; have sharp spines

Echinoderm Reproduction

both sexually and asexually; sexually usually via external fertilization;

Echinoderms in the Environment

marine ecosystems (acting as algae grazers, scooping up detritus, hunting other animals); food source for humans; source of limestone to fertilize farm fields