Starfishes, sea urchins, sea cucumbers Phylum Echinodermata Starfishes, sea urchins, sea cucumbers

General Characteristics Echino- (spiny) derm (skin) Exclusively Marine – usually shallow, coastal waters and ocean trenches Unsegmented Body Larvae are free-swimming and bilaterally symmetrical Adults become bottom-dwelling with radial symmetry Most have five radii or multiples of five which is known as pentaradial symmetry Unique water vascular system

General Characteristics cont. First phylum with endoskeleton (with exceptions) With dermal calcium plates (calcareous ossicles) Some with protruding spines or spicules Complete Digestive System No defined circulatory, respiratory, or excretory systems (no kidneys) Instead, have tiny tube feet that aid in movement, feeding, respiration, and excretion Distinct males and females reproduce sexually and/or asexually Have a nervous system but no head or brain.

Class Asteroidea (“star-like”) Examples: Sea Stars Found all over coastal shores around the world Use tube feet to pry open the shells of oysters, clams, and other sea food that are used by people 4

Body Plan of the Sea Star Oral surface: mouth located on the underside of the body Aboral surface: top of the body (anus is located here) Ossicles: sharp protective spines made of calcium plates, covered with thin epidermal layer (this is what makes it spiny) Pedicellariae: tiny forceps that camouflage or clean the body surface (white structures) 5

External Anatomy Aboral Surface Oral Surface

Internal Anatomy

Asteroidea – Sea Star

Class Ophiuroidea (“snakelike”) Examples: Basket Stars & Brittle Stars Largest echinoderm class Primarily reside under stones & in crevices and holes of coral reefs Thin brittle arms that break off & regenerate themselves quickly Feed by raking food off the ocean floor with their arms and bottom of tube feet Trap food with mucous strands between their spines. 9

Ophiuroidea (“snakelike”) No anus Madreporite on oral surface rather than aboral surface No suckers on tube feet, no ampullae (have a valve to control water pressure) No pedicellariae Gametes (sperm or eggs) released through bursal slits 10

Brittle star anatomy

Ophiurodea – Brittle Star, Basket Star

Class Echinoidea (“hedgehoglike”) Examples: Sand Dollars and Sea Urchins Sand Dollar: Live along seacoasts & sandy areas Flat, round shape bodies Adapted for shallow burrowing Short spines allow for movement (also aid in burrowing & cleaning their bodies) Use tubes to filter food out of water 13

Class Echinoidea Sea Urchins: Test: rigid endoskeleton that the internal organs are compacted in Aristotle’s lantern: complex jaw-like mechanism that is used to grind their food Tube feet allow for movement Barbs on their long spines are sometimes venomous provide protection from predators 14

Anatomy of a Sea Urchin

Aristotle’s Lantern – Sea Urchin

Echinoidea – Sea Urchin, Sand Dollar

Class Holothuroidea Example: Sea cucumbers Bodies are soft Skeletal system reduced or absent No spines or pedicellariae Feed by sweeping up sediment from the water with tentacles around mouth Protect themselves by ejecting internal organs through the anus. Lost parts are later regenerated which is a process called evisceration. 18

Sea Cucumber Anatomy

Holothuroidea – Sea Cucumber

Class Crinoidea (“lilylike”) Examples: Sea lilies and Feather stars Sessile They have long stalks that attach to rocks or to the ocean floor Feather stars eventually detach themselves Sticky tube feet that are at the end of each arm catch food and serve as a respiratory surface. 21

Crinoidea – Sea Feathers, Sea Lily

Class Concentricycloidea Examples: Sea Daisy Less than 1 cm in diameter (so extremely small) Disc-shaped with no arms Tube feet are located around the disc-shaped center Looks very much like a daisy 23

Class Concentricycloidea Example: Sea Daisy

Other Structures 25

Water-Vascular System Hydrostatic pressure permits movement Path of water in the Water-Vascular System Enters sieve plate Passes through stone canal Traces a path from the ring canal encircling mouth to 5 radial canals that extend to each arm Ampulla: bulblike sac that each foot connects to Tube feet contract so that water enters; this allows them to be able to suction onto the surface of slippery rocks 26

Other Body Parts Fluid in coelom bathes organs to distribute nutrients & oxygen Skin gills: protect coelom lining; gases are exchanged Nerve ring: surrounds mouth & branches off into nerve cords in each arm. Eyespots: end of each arm that responds to light 28

Reproduction Sexually reproduces with each arm producing sperm or egg Releases sperm or egg into the water for fertilization (oviparous fertilization) Bipinnaria: a fertilized eggs develops into a free-swimming larva settles in the bottom and develops into an adult through metamorphosis Asexually reproduces by regenerating lost parts 29

Larval Echinoderms with bilateral symmetry