Protostomes and Deuterostomes.

Protostomes	Deuterostomes
Cell division determinate (each cell has a predetermined goal eg skin)	Cell division indeterminate (each cell is more flexible)
Spiral cleavage in embryo	Radial cleavage in embryo
Blastopore forms the mouth	Blastopore forms the anus
Examples: Annelida Mollusca Arthropoda	Examples: Echinodermata Chordata

Chapter 31 Phylum Echinodermata

10,000 species. Deuterostomes (like chordates). Echinoderms are marine predators. Coelomate, radial symmetry ( often in 5 parts eg starfish ). They have characteristic tube feet for movement connected to a water vascular system. Starfish movement (movie)

They have an open circulatory system. Echinoderms absorb oxygen through the skin "dermal gills".
They are mainly dioecious; release sperm and egg into water. Larvae have bilateral symmetry, but later this turns into radial symmetry.

Classes of Echinodermata

Class Asteroidea ( starfish or sea stars)
They have thick arms, and tube feet with suckers. They feed by pulling open bivalves mollusks with their tube feet.
Pedicellaria remove algae etc from their skin. Asteroidea Example : Asterias

Class Ophiuroidea ( brittle stars )
Have long, thin arms that can hold onto rocks etc with snakelike movement. Their tube feet lack suckers, they feed on small particles (filter feeders). Ophiuroidea have a mouth but no anus.

Like most echinoderms, brittle stars have excellent regeneration. If they lose an arm, they grow another one. They rarely get infected, because they have mutualistic bacteria inside them that kill harmful bacteria.
Example : Gorgonocephalus

Class Echinoidea ( sea urchins, sand dollars )
They have no arms. Sea urchins have long spines, sand dollars short spines. Sand dollars have jaws in an area called Aristotles lantern.

Sea urchins have a siphon to divert water from the intestine. Some sea urchins are the longest-lived animals on the planet, surviving over 200 years. The genome of sea urchins was worked out in 2006. Sea urchins share 7,000 genes with humans, so researchers are hoping to learn more about human diseases by studying sea urchins.
Example : Mellita ( sand dollar ).

Class Holothuroidea ( sea cucumbers, sea slugs )
No arms or spines. They have a tubular body with 5 rows of tube feet.

Protection from predators: sticky tubules of Cuvier
They can also eviscerate themselves (cut out their gut and spit it into the water). They then regenerate their gut.

Gas exchange is through a respiratory tree near the anus. Holothuroidea. Sea cucumbers are eaten in Asia, and were harvested in California and Maine. Due to overfishing, the California sea-cucumber fishery was closed in 2000. Example : Cucumaria

Last edited November 2009, David Byres, dbyres@fscj.edu