ROLL CALL 95 



PHYLUM X — ECHINODERMATA — Starfishes, sea-urchins, sea-curumbors. 



Characteristics : Adults radially symmetrical (pentamerous) ; marine ; 



tube-feet, water vascular system, distinct alimentary canal, large body 



cavity usually present ; frequently a spiny skeleton of calcareous plates ; 



larvae bilaterally symmetrical ; 4800 species. 



Class I — Asteroidea — Starfishes (Asterias, Mediaster). 



Characteristics : Typically five rays or arms not marked off from central 

 disk ; each ray possessing ventral ambulacral groove through which numer- 

 ous tube-feet extend ; gastric pouches and hepatic caeca extend into rays ; 

 blunt spines and pedicellariae present; respiration by dermal branchiae. 



Class II — Ophiuroidea — Brittle-stars (Ophiopholis, Ophiothrix, Ophioglypha, 

 Ophioderma). 

 Characteristics: Typically pentamerous with arms sharply marked off 

 from disk ; no ambulacral groove ; hepatic caeca and anal opening lacking. 



Class III — Echinoidea — Sea-urchins, sand-dollars, spatangoids (Arbacia, 

 Strong ylocentrotus, Echinarachnius, Spatangus, Moira). 

 Characteristics : Typically pentamerous without arms or free rays ; test 

 of calcareous plates bears movable spines; i)ediceilariae usually three- 

 jawed ; mouth with five conspicuous teeth constituting part of Aristotle's 

 lantern. 



Class IV — Holothuroidea — Sea-cucumbers {Holothuria. Thyone, Leptosy- 

 napta). 

 Characteristics : Long, ovoid, soft-bodied cchinoderms ; tentacles about 

 mouth; body wall muscular ; skeleton greatly reduced. 



Class V — Crinoidea — Sea-lilies or feather-stars {Antcdon, Halhromelra, Co- 

 rnadinia, Pentacrinus). 

 Characteristics : Usually five branched arms, possessing featherlike divi- 

 sions (pinnules) ; aboral pole sometimes possessing cirri but more gener- 

 ally a stalk for temporary or permanent attachment ; a few modern types, 

 most forms known as fossils. 



