NO. 6 ECHINOID DISTRIBUTION AND HABITS — KIER, GRANT 1 3 



Occurrence. — Eucidaris tribuloides was found only seaward from 

 the "back-reef channel," although it was found much nearer shore 

 farther south off Molasses Key. It is widespread but not abundant 

 in the Coral Reef Preserve, occurring in depths from intertidal to at 

 least 85 feet. It lives on sandy or rocky bottoms (pi. 2, figs. 1-3) 

 but was not found on clean sand where grass or algae were absent. 

 This species lives in the same kind of environment as Lytechinus 

 variegatus, Tripneustes ventricosus, and Arbacia punctulata, but its 

 distribution seems to be most nearly coincident with that of T. 

 ventricosus in this area; it is not as widespread as L. variegatus 

 (fig. 7). Normally it is solitary and well camouflaged, so in light of 

 observed occurrences elsewhere in the Keys, we believe that an 

 intensive search for this species would extend its range in the Coral 

 Reef Preserve to the region nearer shore. 



This species was found at stations 1, 2, 10, 11, 12, 22, 24, 30, 36, 

 38, 51, 52, and 53. 



Behavior. — Eucidaris tribuloides lives unburied, on rocky (pi. 2, 

 fig. 1) or sandy bottoms (pi. 2, figs. 2, 3) but not in areas of clean, 

 grass-free sand. Specimens were found in dense and sparse turtle 

 grass, normally with their upper and lateral primary spines covered 

 by sheaths of living algae which render the animal nearly invisible 

 (pi. 2, figs. 2, 3). Individuals living in grass normally were solitary, 

 whereas those living on rock, under the overhang of a sponge or coral 

 were more typically clustered in favorable niches. Some lived under 

 slabs of rock in shallow water, and in deeper water where slabs had 

 fallen into deep "grooves" between spurs of the reef. 



Mortensen ( 1928, p. 404) reports that this species feeds on algae 

 and Bryozoa. Its abundant presence in areas of turtle grass leads us 

 to suspect that it also eats grass, although no direct observations of 

 its feeding habits were made. This species is relatively immobile 

 during the day; its nocturnal behavior is unknown. We observed no 

 trails, and did not see undisturbed specimens in motion. 



Order Diadematoida Duncan 



Family DIADEMATIDAE Peters 



Genus DIADEMA Gray 



DIADEMA ANTILLARUM Philippi 



Plate 2, figures 4-7 



This black urchin has extremely long, slender hollow spines the tips 

 of which are mildly venomous. The urchin is very large, many adults 



