NO. 6 ECHINOID DISTRIBUTION AND HABITS — KIER, GRANT 33 



up centrifugal currents that move the particles to the periphery and 

 to the lunules. Cilia at the bases of spines on the ventral surface set 

 up centripetal currents that are especially strong in the radial food 

 tracts, moving the food particles medially toward the mouth. Thus the 

 animal collects any food particles contained in any of the sand through 

 which it passes, regardless of whether that sand passes over its ventral 

 or oral surface. 



Genus ENCOPE Agassiz 



ENCOPE MICHELINI Agassiz 



Plate 5, figure 7; plate 7, figures 1-8; plate 15, figure 7; text figure 7 



When alive this sand dollar has a dark brown to reddish brown test 

 covered with very short, dense spines. The test is flat, with one large 

 slotlike lunule between the posterior petals, and usually five indenta- 

 tions in the ambulacra at the margin. An adult is approximately 

 100 mm. long. It is distinguished from the other sand dollar asso- 

 ciated with it. Leodia sexiesperforata, by its larger, thicker test, 

 longer petals, darker color, and presence of ambulacal indentations 

 at the margin rather than perforations. It is similar to E. emarginata 

 (Leske), with which it has been confused, but differs in having its 

 adapical surface elevated posterior to the apical system whereas, in 

 E. emarginata the test is flattened adapically. Furthermore, the in- 

 dentations of E. emarginata are usually closed whereas those of E. 

 michelini are open, where present. All the specimens we collected off 

 the Keys had indentations, but they are absent on many of the speci- 

 mens from the Gulf of Mexico. Thomas F. Phelan, research 

 assistant at the U.S. National Museum, is currently making a study 

 of the variation in these characters in the Carribbean and Gulf 

 Encope. 



Occurrence. — Encope michelini was found only in areas of deep 

 sand with little or no turtle grass or filamentous algae. The surface 

 of the sand normally is marked by large ripples up to 4 inches high 

 and 12-16 inches between crests, although these are a function of 

 wave oscillation and are rapidly destroyed by the echinoids on calm 

 days. The species normally burrows through the upper surface of the 

 sand, rarely covering its upper surface to a depth of more than one- 

 quarter inch. Normally E. michelini is associated with Leodia 

 sexiesperforata on the broad sandy reaches of the White Bank 

 (fig. 7). Although it is much more abundant than L. sexiesperforata 



