14 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 149 



being more than 200 mm. in horizontal diameter with spines, 100 mm. 

 without. The bare test is flattened and the apical system and medial 

 areas of the interambulacra are depressed. The ambulacra are narrow, 

 inflated with the pore-pairs in two fairly straight series in each area. 

 Spines of mature specimens are black, but those of juveniles are 

 annularly banded black and white. Kristensen (1964, p. 15) reports 

 that adults with gray or banded (or white) spines occur in areas of 

 low light intensity, either deep or turbid water. 



Occurrence. — Diadema antillarum is the most ubiquitous echinoid 

 in the area of the Coral Reef Preserve. It occurs in the entire depth 

 range studied, and extends from intertidal slopes of South Sound 

 Creek leading from Largo Sound, to a depth of 110 feet on the sea- 

 ward side of the main reef, and undoubtedly much deeper. Mortensen 

 (1940, p. 274) reports it from depths as great as 1,200 feet. It was 

 found among mangrove roots in South Sound Creek (station 40) and 

 in irregularities in the limestone bottom of that creek, in sparse grass 

 on open sand in large flocks near Rodriguez Key, in denser grass in 

 Hawk Channel where the water is cloudy with suspended silt, in 

 isolated reef patches within the sandy areas, in clear water at all 

 depths on the main part of the reef, on sand terraces beyond the reef, 

 and on discontinuous reef mounds in deep water beyond the reef. 

 The only environment from which D. antillarum was absent is open 

 grassless sand, the areas primarily inhabited by sand dollars and 

 Mcoma ventricosa. 



This species was found at stations 1, 3, 4, 10, 11, 11a, 12, 13, 15, 

 16, 17, 17a, 18, 22, 25, 26, 27, 28, 31, 32, 36, 38, 40, 43, 50, 52, and 59. 



Behavior. — Diadema antillarum remains relatively immobile during 

 the day. It occupies niches and recesses in the reef or other rock, rests 

 among mangrove roots (even on nearly vertical sides of creeks), hides 

 under rock slabs in shallow water where dead reef is broken by wave 

 action, or in deeper water between reef masses, or it gathers into 

 clusters and spends the day on the sand among sparse turtle grass 

 and other vegetation. Specimens were found around the bases of 

 isolated sponges or corals, and even living inside the cups of larger 

 basket sponges. 



Individuals remain in their niches, gently waving their long spines 

 (or having them waved by the surge of water), with small white 

 mysid shrimps swimming among the spines. Upon approach of 



