ECHINODERMATA (e-kī′nō-der′m ă -t ă )

GERM LAYERS  Echinoderms have three germ layers (triploblastic)  Endoderm becomes the digestive tube (archenteron)  Mesoderm creates future skeleton, between the endoderm and ectoderm  Ectoderm becomes the outer layer

COELOM  Def: A body cavity (fluid or air filled space separating the digestive tract from the outer body wall) lined by tissue derived only from mesoderm.  In deuterostomes, the mesoderm buds from the wall of the archenteron, so the cavity made becomes the coelem

SYMMETRY  Only adults have radial symmetry; echinoderm larvae are bilaterally lateral and later develop pentaradial symmetry  The body is arranged in five parts around a central axis

DIGESTIVE TRACT  Very simple digestive gut  Leads from mouth to stomach to anus

CEPHALIZATION  Definition: an evolutionary trend toward the concentration of sensory equipment the anterior and of the body.  Echinoderm have no sensory head region.  Have a diffuse network of nerves and neurons that make a ring around the mouth

SEGMENTATION  Echinoderms have no segmentation

SKELETON AND APPENDAGES  Echin- spiny, derma-skin  Thin epidermis covers a hard, flexible endoskeleton made of calcareous plates  No appendages; organs found in all spokes of the body

CIRCULATORY SYSTEM  Echinoderms have no well defined circulatory system  Open circulatory system- fluid bathes organs directly with oxygen with no distinction between blood and other fluid

RESPIRATORY SYSTEM  A very simple system  They have gills and tube feet to take in oxygen and take out carbon dioxide.

REPRODUCTION  Echinoderms are gonochric (separate sexes)  Fertilization is external- gametes are released into the water  They have free living larva

HABITAT  Echinoderms are found at every ocean depth from the seashore (intertidal zone) to the very bottom of the ocean (abyssal zone)

FUN FACTS  Water Vascular System- unique to echinoderms. It is a network of hydraulic canals branching into extensions, called tube feet, that work in locomotion, feeding, and gas exchange.