Phylum Echinodermata Marine Invertebrates

Characteristics All marine Known as spiny-skinned animals Endoskeleton known as the test is made of calcium plates or ossicles with protruding spines Includes sea stars, brittle stars, sand dollars, sea urchins, & sea cucumbers

Characteristics Bipinnaria Larva Undergo metamorphosis from bilateral, free-swimming larva to sessile or sedentary adult Larval stage known as dipleurula or bipinnaria Adults have pentaradial (5 part) symmetry Lack segmentation or metamerism

Characteristics Coelomate Breathe through skin gills as adults Capable of extensive regeneration

Characteristics Ventral (lower) surface called the oral surface & where mouth is located Dorsal (upper) surface known as aboral surface & where anus is located Have a nervous system but no head or brain in adults No circulatory, respiratory, or excretory systems

Characteristics Have a network of water-filled canals called the water vascular system to help move & feed Tube feet on the underside of arms help in moving & feeding One-way digestive system consists of mouth with oral spines, gut, & anus Deuterostomes (blastopore becomes the anus)

Characteristics Separate sexes Reproduce sexually & asexually In sexual reproduction, eggs (up to several million) from females and spermatozoa from males are shed into the water (spawning), where the eggs are fertilized. Most echinoderms spawn on an annual cycle, with the spawning period normally lasting one or two months during spring or summer; several species, however, are capable of spawning throughout the year. Spawn-inducing factors are complex and may include external influences such as temperature, light, or salinity of the water.

Includes 5 classes: Crinoidea - sea lilies & feather stars Asteriodea - starfish Ophiuroidea - basket stars & brittle stars Echinoidea - sea urchins & sand dollars Holothuroidea - sea cucumbers

1) Crinoidea Characteristics Sea lilies & feather stars Sea lilies have a long stalk with branching arms that attach them to rocks & the ocean bottom Feather stars can detach & move around Mouth & anus on upper surface

1) Crinoidea Characteristics May have 5 to 200 arms with sticky tube feet to help capture food (filter feeders) & take in oxygen Common in areas with strong currents & usually nocturnal feeders

2) Asteroidea Characteristics Usually sedentary along shorelines Starfish or sea stars Come in a variety of colors Prey on bivalve mollusks such as clams & oysters

2) Asteroidea Characteristics Have 5 arms that can be regenerated Arms project from the central disk Mouth on oral surface (underside) Range in size from  1 cm to 1 m

Body Plan of Sea Star Have an endoskeleton made of calcium plates Sharp, protective spines made of calcium plates called ossicles found under the skin on the aboral (top) surface Have pedicellariae or tiny, forcep-like structures surrounding their spines to help clean the body surface Aboral Surface

Water Vascular System Network of canals creating hydrostatic pressure to help the starfish move Water enters through sieve plate or madreporite on aboral surface into a short, straight stone canal Stone canal connects to a circular canal around the mouth called the ring canal

Water Vascular System Five radial canals extend down each arm & are connected to the ring canal Radial canals carry water to hundreds of paired tube feet

Water Vascular System

3) Class Ophiuroidea Largest class of echinoderms Includes basket stars & brittle stars Live on the ocean bottom beneath stones, in crevices, or in holes

3) Class Ophiuroidea Have long, narrow arms resembling a tangle of snakes Arms readily break off & regenerate Move quicker than starfish Feed by raking in food with arms or trapping it with its tube feet

4) Class Echinoidea Includes sea urchins & sand dollars Internal organs enclosed by endoskeleton or test made of fused skeletal plates Body shaped like a sphere (sea urchin) or a flattened disk (sand dollar) Lack arms

4) Class Echinoidea Bodies covered with movable spines Have a jawlike, crushing structure called Aristotle's lantern to grind food Use tube feet to move

4) Class Echinoidea Spherical shape Live on ocean bottom Scrape algae to feed Long, barbed spines make venom for protection

4) Class Echinoidea Flattened body Live in sand along coastlines Shallow burrowers Have short spines

5) Class Holothuroidea Includes sea cucumber Lack arms Shaped like a pickle or cucumber Live on ocean bottoms hiding in caves during the day  Have a soft body with a tough, leathery outer skin

5) Class Holothuroidea Five rows of tube feet run lengthwise on the aboral (top) surface of the body Have a fringe of tentacles (modified tube feet) surrounding the mouth to sweep in food & water Tentacles have sticky ends to collect plankton Show bilateral symmetry Can eject parts of their internal organs (evisceration) to scare predators; regenerate these structures in days

5) Holothuroidea Bulb-like sacs or ampulla on the upper end of each tube foot contract & create suction to help move, attach, or open bivalves Rows of tube feet on oral surface (underside) are found in ambulacral grooves under each arm

Feeding & Digestion Tube feet attach to bivalve mollusk shells & create suction to pull valves apart slightly Starfish everts (turns inside out) its stomach through its mouth & inserts it into prey Stomach secretes enzymes to partially digest bivalve then stomach withdrawn & digestion completed inside starfish