ECHINODERMATA
(e-kī′nō-der′mă-tă)
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.