I'HYLUM ECHINODERMATA 



515 



Figure 198. Starfish collected by dragging a mop 

 of threads behind a boat. (Courtesy of General 

 Biological Supply House, Inc.) 



CLASSIFICATION OF 

 THE ECHINODERMATA 



(For reference purposes only) 



Echinodenns are radially symmetrical as 

 adults but bilaterally symmetrical as larvae; no 

 segmentation; the body wall usually contains 

 calcareous plates that form an endoskeleton; 

 nervous system with oral nerve ring and radial 

 nerves; sexes usually separate; a water-vascular 

 system, including tube feet, is usually present. 

 The 6000 known species are placed in 5 

 classes as follows: 



Class 1. Crinoidea (Gr. krinon, lily). Sea 

 lilies (Fig. 190). Adults usually with 

 5 branched rays and with pinnules; 

 cuplike calyx; tube feet suckerlcss; 

 aboral pole sometimes with cirri, but 

 only about 60 out of 630 existing 

 species possess a stalk for temporary 

 or permanent attachment; few mod- 

 ern species but many fossils. Ex. An- 

 tedon tenella, sea lily. 



Class 2. Asteroidea (Or. aster, star). Star- 

 fishes (Fig. 190). Adults typically 

 with 5 rays; rays usually not sharply 

 marked off from disk; ambulacral 

 grooves open with tube feet; madre- 

 porite aboral; respiration by dermal 

 branchiae. Ex. Asterias forbesi, star- 

 fish. 



Class 3. Ophiuroidea (Or. op/iis, snake). Brit- 

 tle stars (Fig. 190). Typically 5 rays; 

 rays sharply marked off from distinct 

 disk; flexible rays; no ambulacral 

 grooves; no pedicellariae; madreporite 

 oral. Ex. Ophioderrna brevispinum, 

 brittle star. 



Class 4. Echinoidea (Gr. echinos, spiny). Sea 

 urchins (Fig. 190). Body hemispheri- 

 cal, egg-shaped, or disk-shaped; no 

 free rays; skeleton of calcareous plates 

 forming a test, bearing movable 

 spines; usually three-jawed pedicel- 

 lariae; tube feet with suckers. Ex. 

 Echinarachnius parma, sand dollar. 



Class 5. Holothurioidea (Gr. holothourion, 

 sea cucumber). Sea cucumber (Fig. 

 190). Adult body long, ovoid, and 

 soft, with muscular wall; retractile 

 tentacles around mouth; body wall 

 usually contains calcareous plates; no 

 rays; no spines nor pedicellariae; tube 

 feet usually present; cloaca usually 

 with respiratory tree. Ex. Thyone 

 briareus, common sea cucumber. 



SELECTED COLLATERAL 

 READINGS 



Clark, A.H. "Sea Lilies and Feather Stars." 

 Sinithsonian Misc. Collections, 72, No. 7, 

 1921. 



Coe, W.R., "Echinoderms of Connecticut." 

 Connecticut State Geological and Natural 

 History Survey, Bull. 19, 1912. 



Harvey, E.B. The American Arbacia and Other 

 Sea Urchins. Univ. Press, Princeton, 1956. 



Hyman, L.H. The Invertebrates: Echinoder- 

 tnata. McGraw-Hill, New York, 1955. 



Jennings, H.S. "Behavior of the Starfish Aste- 

 rias forreri DcLoriol." Univ. Calif. Pub. 

 Zoo/., 4:53-185. 1907. 



