NO. 6 ECHINOID DISTRIBUTION AND HABITS — KIER, GRANT 25 



Lewis (1958) mentions the similarity in occurrence and habitat of 

 these two species, but apparently some rather important differences 

 in requirements also exist. 



This species was found at stations 10, 11, 12, 27, 28, 29, 30 (juve- 

 niles), 38 (juveniles), 44, 51, and 52. 



Behavior. — Tripneustes ventricosus lives on the sandy bottom 

 among the turtle grass, and also climbs up the grass blades for a short 

 distance above the bottom. According to Lewis (1958) it feeds almost 

 exclusively on algae that grows on and among the rocks near shore. 

 We made no systematic observations on the feeding habits of this 

 species, but its association with L. variegatus in turtle grass, and its 

 habit of climbing in the grass, indicate that it may eat turtle grass as 

 well as algae. However, blades of Thalessia are frequently coated 

 with a thin floral slime and it may be that T. ventricosus climbs on the 

 grass in order to feed on the slime. Lewis reports that it rejects 

 calcareous algae such as Halimeda. Kier has observed the same species 

 living on rock near the shore of the island of Dominica, in an environ- 

 ment similar to that described by Lewis off Barbados. There likewise 

 the available food was algae growing upon rock. 



The habit of covering the test with shells, leaves, or other objects 

 is much less strongly developed in this species than in L. variegatus 

 (pi. 3, fig. 2) . Individuals of the two species living within a foot or 

 two of one another exhibited greatly differing amounts of cover, 

 with T. ventricosus normally nearly uncovered, and L. variegatus 

 ranging from sparsely covered to almost entirely concealed. Small 

 individuals on the other hand, seemed to seek protected places under 

 rocks, or in clumps with other small specimens (of this species and 

 L. variegatus) with elaborate coverings of shells, sponges, and other 

 objects in an intricate tangle. It would be interesting to discover 

 whether they can drop or abandon this cover at night, and regain or 

 reconstruct it each day, as reported for normal size L. variegatus by 

 Sharp and Gray (1962). 



Order Holectypoida Duncan 



Family ECHINONEIDAE Wright 



Genus ECHINONEUS Leske 



ECHINONEUS CYCLOSTOMUS Leske 



Plate 15, figure 1 



The only holectypoid found, this species is easily identified because 

 of its large oblique peristome, with the large periproct situated just 



