Unit 14 - Echinoderms

Pentaradial symmetry, central disk, arms in multiples of 5, oral and aboral surfaces, larvae are bilaterally symmetrical, large coelom is main body cavity.

False, no head or metamerism

Dermal ossicles or spicules

Protrudes as spines

Pincer-like structure that helps keep body surface clean, protects papulae and helps in feeding.

Papulae (gills)

A porous screen that lets water in

Madriporite connects to stone canal, connects to ring canal, leads to radial canal. 1 per arm.

Tube feet used for food gathering and locomotion. Compression of ampulla elongates tube foot. Suckers often at end of tube feet.

Complete alimentary canal, short esophagus, cardiac stomach often evertable, pyloric stomach connects to pyloric ceca (digestive gland), short intestine leads to anus.

Pyloric ceca produce digestive enzymes and are also sites of digestion and absorption.

Coelomic fluid is circulated by cilia on the cells of the peritoneum. Gas exchange happens across thin walls in tube feet and papulae. Nitrogenous waste can be removed by coelomocytes

Nerve ring surrounds the esophagus, radial nerve cords under radial canals of water vascular system in the ambulacral groove

Crinoidea, Asteroidea, Echinoidea, Ophiuroidea, Holothuroidea

Sea lillies and feather stars, sessile in early part of life, tube feet and mouth faces up, No madreporite, spines or pedicellariae, has central disc called calyx

Sea stars, regenerators, predators to anything they can catch, feed on bivalves with 1k force.

Sea urchins and sand dollars, no arms, dermal ossicles connected to one large test. Powerful toothed chewing structure called aristotle's lantern for grazing on algae.

Brittle stars, Slender arms covered by articulated ossicles, Ambucural grooves covered.

Sea cucumbers, elongate and soft bodied, spicules, bilaterally symmetrical, Cuvierian tubules, tube feet.