echinoderms

PHYLUM ECHINODERMATAEchinoderms: Sea stars, brittle stars, feather stars, sea cucumbers, sea urchins

CHARACTERISTICS

•Radial symmetry

• Several arms (5 or more, mostly grouped 2 left- 1 middle- 2 right) radiating from a central body.

•Body consist of equal segments, each containing a duplicate of various internal organs.

CHARACTERISTICS•No brain nor hearts•With eyespots on each arm•Mouth situated on the underside and anus on top (except feather stars, sea cucumbers and some urchins).• Contains tube feet with suction pads controlled by water vascular system.

CHARACTERISTICS

• Some are carnivorous while others are detritus foragers.•Reproduction is through release of sperms and egg into the water.•Capable of regeneration and fragmentation.

TYPES OF ECHINODERMS

•Class Asteroidea•Class Ophiurodea •Class Echinoidea•Class Holothuroidea•Class Crinoidea

WHAT IS THIS?

• Cushion starfish (Culcita nouvaeguineae)

CLASS ASTEROIDEA

•Carnivorous and feed on sponges and molluscs some are specialized feeders.(crown of thorns)•Doesn’t have hard mouth parts to help them capture prey.

TRIVIA

• Crown of thorns (Acanthaster planci)•One of the largest and the most venomous starfish.• Size reaches up to 50 cm in diameter.• 10 to 20 spiny arms with formidable thorn like toxic spines• Feed on coral polyps• Predators: Triton shell and some puffer fish

CROWN OF THORNS (ACANTHASTER PLANCI)

CLASS OPHIUROIDEA

•Close relatives of sea stars•Have five snakelike arms which are highly flexible.•No replication of internal organs, just one set in the central disk.•Smaller central disk and no anus.

•Arms of brittle stars are fragile. ( Defense Mechanism) •Most active and fastest moving echinoderms•Feed on plankton but also on detritus.

• Serpent Stars• Coiled snakelike around branches of gorgonians.

TRIVIA

• Basket stars• Specialized type of brittle stars

(Astroglymma sculptum)

CLASS ECHINOIDEA

Sea urchins• External chitinous skeleton and a centrally located jaw• Some have speherical bulb-like cloaca.•Movable spines are attached to the body, some are venomous

• Locomotion by tube feet but also by movement of the spines on the underside of the body.•Generally nocturnal•Most are algal grazers but some feed on sponges and detritus.

CLASS HOLOTHUROIDEA

•Don’t have radial symmetry but are bilateral.•Cucumber shaped with elongated muscular, flexible body with mouth at one end anus on the other.• Tentacles present in the mouth for food collection

•Feed on rich organic film coating sandy surfaces.•Crawl over the bottom and ingest sand.•Move by means of tube feet.•Releases its digestive tract when threatened (defense mechanism)

PHYLUM CRINOIDEA

•Radial symmetry•Cup-shaped body •Numerous feathery arms project from a central disc.•Have 5 up to 200 arms (pinnules)•Nocturnal •Usually cling to sponges.

FEATHER STARS

• Source: http://www.starfish.ch/reef/echinoderms.html#starfish