NO. 6 ECHINOID DISTRIBUTION AND HABITS — KIER, GRANT 15 



danger, presumably sensed by motion or the shadow cast by the po- 

 tentially dangerous object, D. antillarum begins to wave its spines 

 rather rapidly. When the potential danger is a diver, they seem to 

 point many of the spines at him ; presumably this is their reaction to 

 other dangers as well. Specimens that are in the open on grassy sand 

 group their upper spines into five cone-shaped bundles and point them 

 at the intruder, after the fashion observed in Astro pyga magnified 

 (pi. I). 



Shroeder and Stark (1964) report that D. antillarum becomes 

 much more active at night, leaving its niches and wandering about on 

 the reef. Presumably the groups that rest on the grassy sand during 

 the day also become active and more mobile during the night. Other 

 similarities in habit suggest that perhaps the groups remain intact as 

 they move, as do clusters of A. magnified during the day. 



A few individuals were seen living singly on grassy sand, away 

 from reef mounds or other places with available niches. Many of 

 these isolated specimens (pi. 2, fig. 5) were small, with the black and 

 white banded spines characteristic of juveniles. A few adults also 

 were seen alone on sand, but this mode of life seemed to be more 

 typical of the juveniles. 



Genus ASTROPYGA Gray 

 ASTROPYGA MAGNIFICA Clark 



Plate 1, figures 1-5 



This echinoid is striking in appearance with its large test (205 mm. 

 in horizontal diameter including spines) and its radiating color pat- 

 tern. Under water the interambulacra are yellow, the ambulacra 

 brown with brilliant iridescent blue spots bordering the ambulacra. 

 At the surface in natural light unfiltered by the water, the specimens 

 have purplish red (mallow) ambulacra and yellow- white inter- 

 ambulacra. The spines are banded with the same colors. A large anal 

 tube was present on all the living specimens. In shape and size of its 

 test, length and thickness of its spines, this species strongly resembles 

 Diadema antillarum, but is easily distinguished by its color. 



Occurrence. — Astropyga magnified was found only on the sand 

 terrace on the seaward side of the reef, at a depth of 80-85 feet. 

 Mortensen ( 1940, p. 207) reports it from a depth of 88 meters off Dry 

 Tortugas, Fla. We observed it on nearly flat grassless sand which 



