l8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I49 



niches that offer some protection, either from predators or from sun- 

 light (Sharp and Gray, 1962). 



This species was found at stations 24, 27, 46, and 51. 



Behavior. — Arbacia punctulata was not observed to cover itself 

 with objects from the substrate. Sharp and Gray (1962) studied its 

 reaction to various kinds of light, including sunlight, and concluded 

 that it tends to negative phototaxis, although much less strongly than 

 Lytechinus variegatus. They report also that A. punctulata is highly 

 variable in its response to light, with some specimens remaining at 

 water level during low tide, in the full light of the sun. This varia- 

 bility would account for our finding the species clustering under 

 overhanging edges of coral or sponge, and also finding rare individuals 

 on bare rock or uncovered in sparse grass. 



Order Echinoida Clans 

 Family ECHINOMETRIDAE Gray 



Genus ECHINOMETRA Gray 



ECHINOMETRA LUCUNTER (Linnaeus) 



Plate 16, figures 1-4 



The living test is reddish to dark brown, usually slightly oblong, 

 with adults from 80 to 100 mm. long although a few specimens are 

 considerably larger. The spines are long and slender, but moderately 

 thick near their bases. The bare test has large tubercles, two rows of 

 which are larger in each interambulacrum and ambulacrum. The pore- 

 pairs are arranged in arcs, and the peristome is large. This species 

 can be confused with Echinometra viridis Agassiz (distinguished be- 

 low) and with Arbacia punctulata (Lamarck). It differs from A. 

 punctulata in having thicker spines, usually an oblong test, fewer large 

 tubercles, and many periproctal plates. 



Occurrence. — Echinometra lucunter was found in shallow water 

 (2-8 feet), both near shore and on shoals far from shore. Normally it 

 was on hard bottom, either among slabs of dead reef limestone or on 

 small patch reefs in sandy areas. Some were found in sand away 

 from hard substrate, but these were near sponges or small corals, or 

 under clumps of shells, coral, and sponge. The species ranges from 

 the shoreline to exposed parts of the reef. It was found among the 

 rocks along the shore at station 60, and was present in sand in shallow 

 water near Rodriguez Key. In addition, many specimens were found 

 on rock in the shoreline intertidal zone farther south at Molasses Key, 

 where it was found to a depth of 10 feet. 



