Echinoderms Section 38 1 Echinoderms Examples sea stars

Echinoderms Section 38. 1

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

4 Unique Characteristics: 1. Ossicles: calcium carbonate plates that make up exoskeleton 2. 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 Ø 6 classes of echinoderms (only 5 discussed in textbook): Ø Class Crinoidea Ø Class Ophiuroidea Ø Class Echinoidea Ø Class Holothuroidea Ø Class Asteroidea

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

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

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

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

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

Sea Stars Section 38. 1 continued

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

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

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

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

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

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