Echinoderms Section 38.1

Echinoderms Examples: sea stars, sand dollars, sea urchins, & sea cucumbers Marine environments Brilliantly colored Radial symmetry

4 Unique Characteristics: Ossicles: calcium carbonate plates that make up exoskeleton Water-vascular system: network of water-filled canals inside body

3. Tube feet: small, movable extension of w-v system which aid in movement, feeding, respiration, & excretion 4. Pentaradial symmetry: body parts extend from center along 5 spokes

Classification 6 classes of echinoderms (only 5 discussed in textbook): Class Crinoidea Class Ophiuroidea Class Echinoidea Class Holothuroidea Class Asteroidea

Class Crinoidea Examples: sea lilies, feather stars Crinoid means “lily-like” 5 main arms that branch to form up to 200 more arms Filter feeders Mouth faces up

Class Ophiuroidea Largest class with examples such as basket stars & brittle stars Ophiuroidea means “snake-tail” Live on bottom of ocean Regeneration of broken arms Long, narrow arms allow for quick movement

Class Echinoidea Examples: sea urchins & sand dollars Echinoidea means “spinelike” Test: compact, rigid endoskeleton that surrounds internal organs Spines can have barbs or venom

Class Holothuroidea Example: sea cucumber Holothuroidea means “water polyp” Armless Ossicles are not connected thus soft bodies Tentacles around mouth to capture prey

Class Asteroidea Example: sea star (starfish) Asteroidea means “starlike” Variety of sizes, shapes, and colors Compete with humans for oysters, clams, etc

Sea Stars Section 38.1 continued

External Structure Several arms extending from central region Two rows of tube feet on underneath side of each arm Oral surface: side where mouth is located Starfish = underside Aboral surface: side opposite of mouth

Rough texture due to short spines Pedicellariae: tiny pinchers surrounding of each spine that keep body free of foreign objects

Water-Vascular System Network of water-filled canals that are connected to the tube feet Water movement: Madreporite (sievelike plate on aboral surface)  stone canal  ring canal (encircles mouth)  radial canal (extends to each arm)  tube feet Ampulla: bulblike sac at end of tube feet that allows for movement and suction

Feeding & Digestion Prey: mollusks, worms, clams Cardiac stomach: can be turned inside out through mouth during feeding Digestive pathway: Mouth  cardiac stomach  pyloric stomach  digestive glands in each arm  anus

Other Body Structures No circulatory, excretory, or respiratory systems! Skin gills: thin walls of tube feet that allow gas exchange Nervous system = nerve ring (around mouth), radial nerves (length of each arm), eyespots (end of each arm), tentacles

Reproduction & Development Separate sexes – each arm has sex organs External fertilization After 2 months of swimming they settle to bottom of ocean and metamorphous into adult Regeneration (asexual) As long as part of the central region stays in tact