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PACIFIC SCIENCE, Vol. XVII, July 1963 
PHOTOTROPISM 
H. atra, and to an even greater extent, H. 
leucospilota are negatively phototropic since 
both protect themselves from strong light, H . 
atra by its sand coating, and H. leucospilota 
by seeking shelter. They usually react to quick 
changes in light intensity, as by withdrawal of 
tentacles when covered by a shadow during feed- 
ing. H. leucospilota reacts to a shadow by sud- 
denly contracting under the protection of the 
rock where its posterior end is anchored, thus 
frequently requiring a quick grasp and a firm 
pull in order to collect this species. 
PREDATION 
Besides reflective insulation the sand coating 
of H. atra affords concealment. This function, 
however, would seem to be subordinate to that 
of insulation, because of the small amount of 
predation to which H. atra is apparently sub- 
jected, unless, of course, the converse obtains, 
that the small amount of predation may be due 
to the concealing effect of the sand coating. A 
damaged sea cucumber has been observed only 
once. This specimen, presumably pecked by a 
bird, occurred in an area where curlews had 
been active. In no case has an animal been ob- 
served actually preying upon H. atra. Grazier 
(1915:246) observed lightly colored parts of 
Fig. 5. Histogram showing volume-frequency of 
407 H. atra from a pool at Kabelle I., Sept. 14, 1961. 
Fig. 6. Relationship of volume to length of 407 
H. atra at Kabelle I., Sept. 14, 1961. Lines drawn by 
inspection. 
H. surinamensis which he suspected of being 
regenerated following either autotomy or injury 
by enemies such as fishes or crabs, but states 
that there is no evidence that Holothuria has 
enemies of this kind. Frizzell and Exline ( 1955: 
29) ascribe predation on intertidal sea cucum- 
bers to sea gulls, and note the general concur- 
rence among authors that predation is slight, but 
propose that the apparent protective mecha- 
nisms of holothurians suggest predation to be 
more common than is supposed. 
TRANSVERSE FISSION 
Fission has been reported in holothurians by 
Crazier (1915:291), who found regeneration 
of either end of the body in about 10% of the 
H. surinamensis encountered. Frizzell and Exline 
(1955:15 and 27) state that a few forms in- 
cluding Holothuria parvula (Selenka), Cucum- 
aria lactea, and C. planci (Brandt) sometimes 
