NO. 6 ECHINOID DISTRIBUTION AND HABITS — KIER, GRANT \"J 



Order Arbacioida Gregory 



Family ARBACIIDAE Gray 



Genus ARBACIA Gray 



ARBACIA PUNCTULATA (Lamarck) 



Plate 2, figures 8-9 ; plate 10, figure 5 ; text figure 4 



This dark brown urchin is characterized by its long slender spines 

 and circular ambital outline. An adult is approximately 90 mm. in 

 horizontal diameter with spines, 45 mm. without. The area around the 

 apical system is naked and there are usually four large periproctal 

 plates. The dead test is reddish brown, with narrow ambulacra, and 

 pore-pairs arranged in simple vertical series. The tubercles on the 

 interambulacra are of the same size and are arranged in oblique series 

 slanted up to the middle of each area. This species can be confused 

 with Echinometra lucunter from which it is distinguished by its 

 longer slenderer spines and round test, and with Diadema antillarum 

 from which it differs in having thicker solid spines, and a smaller, 

 higher test with a larger peristome. 



Occurrence. — Arbacia punctulata was found primarily in areas of 

 turtle grass, commonly associated with Lytechinus variegatus and 

 Tripneustes ventricosus. During the day it stays in the shadow of an 

 overhanging sponge or clump of coral (pi. 2, figs. 8, 9) although 

 rarely it was merely in grass like the above two species. The species 

 also occurred rarely on sandy areas with little or no turtle grass, 

 although there it stays near corals or sponges. 



This species was rare in the area of study. Its range apparently 

 coincides rather closely with that of Tripneustes ventricosus, but more 

 observations would be necessary in order to establish its limits pre- 

 cisely (fig. 4). It was found in the "back-reef channel" and in Hawk 

 Channel, in depths ranging from 10 to 20 feet. 



Sharp and Gray (1962, p. 309) report A. punctulata living on rocky 

 bottom in about 12 to 20 feet of water off the coast of North Carolina. 

 We encountered large numbers along the rocky shore of Molasses 

 Key, a few miles south of the Coral Reef Preserve. Similarly, Kier 

 has found it on the rocky coast of Dominica in the Lesser Antilles. 

 Only one specimen was found in a rocky habitat in the Key Largo 

 Coral Reef Preserve, exposed and uncovered on bare rock within a 

 large grassy area at station 51. The species obviously inhabits a 

 variety of environments, but seems to have a clear preference for 



