A New Polyclad Turbellarian Associating with a Hermit Crab 
in the Hawaiian Islands 
Stephen Prudhoe 1 
At the request of Dr. Ernst S. Reese of the 
University of Hawaii the writer has studied 
seven specimens of a polyclad turbellarian 
found in the shells of Trochus sandwich ensis 
occupied by the hermit crab Calcinus latens in 
Kaneohe Bay, Oahu, Hawaiian Islands. Accord- 
ing to Dr. Reese (in litt.) the worm wraps 
itself around the abdomen of the crab and 
usually occurs deep in the spiral cavity of the 
molluscan shell. When dislodged from its shel- 
ter and placed in a dish of water together with 
the crab in its shell, the worm tries to re-enter 
the shell, but only one case was actually seen 
of the worm entering. The frequency with 
which this association occurs is about one per 
25-30 crabs, but a particularly high incidence 
of four worms to 60 crabs was found on March 
7, 1967, in the same location in Kaneohe Bay. 
Apparently the polyclad has not been found 
in the shells of other hermit crabs, Calcinus 
laevimanus and Clihanarius zebra, associating 
with Calcinus latens, although the three species 
use Trochus sandwichensis shells, and the only 
ecological difference between them is that 
Calcinus latens extends further down into the 
sub-tidal than does either of the other two 
species. 
The present specimens undoubtedly belong 
to the genus Emprosthopharynx and appear to 
represent a new species. They were first noticed 
by Dr. Reese’s research assistant, Mrs. Anne 
Phillips Rasa, and the writer has much pleasure 
in naming the species after her. 
The writer would like to thank Dr. Reese for 
giving him the opportunity of examining the 
worms, and for providing information on their 
behaviour. The type specimens are deposited in 
the collections of the British Museum (Natural 
History). 
1 Department of Zoology, British Museum (Natural 
History). Manuscript received June 27, 1967. 
Emprosthopharynx rasae sp. nov. (Figs. 1-3) 
In life, the worms are light reddish brown to 
tan, with somewhat paler margins, but when 
preserved in glycerine-alcohol the body is 
whitish, with the dorsal surface in mature 
specimens being faintly mottled with brownish 
spots which appear to be ovaries lying beneath 
the wall of the body. The seven specimens avail- 
able are in varying stages of development. Of 
the two largest mature specimens, one measures 
20 mm in length and 6.5 mm in maximum 
width, and the other 18 mm long and 7.0 mm 
wide. The body is elongate oval in outline and 
tapering somewhat at both ends. It is dorso- 
ventrally flattened and measures about 1 mm in 
maximum thickness. No tentacles or indications 
of them have been made out. The cerebral organ 
is relatively small and lies in the median line at 
about 2.5 mm from the anterior margin of the 
body in the larger specimens. 
The eyes, which are not numerous, are very 
small and mainly submarginal in the anterior 
region of the body. A few, however, lie in the 
cerebral area. The submarginal eyes form a band 
extending posteriorly to a level close behind the 
cerebral organ. The eyes occurring in the region 
of the cerebral organ are disposed in four 
groups (Fig. 2). Two of the groups are located 
one on either side of the cerebral organ; each 
consists of a pair of eyes, and these may be 
regarded as the tentacular eyes. Sometimes the 
tentacular eyes divide, and therefore three or 
four eyes may be seen in one group. The other 
two groups, each containing from three to five 
eyes arranged more or less in a row in front 
of the cerebral organ, may be considered as the 
cerebral groups, which lie more ventrally in the 
parenchyma than the tentacular eyes. 
In a complete specimen stained with Mayer’s 
paracarmine there is a submarginal area around 
the whole body which stains a deeper hue than 
the rest of the body wall. From serial sections 
408 
