Feeding Habits of the Sand Crab Hippa pacific a (Dana ) 1 
Donald C. Matthews 2 
Burrowing sand crabs, Hippa pacifica 
(Dana), [Remipes pacifica Dana of Edmondson, 
1925; Emerita pacifica (Dana) of Edmondson, 
1946, and Bonnet, 1946], were observed feed- 
ing on Portuguese man-of-war ( Physalia utri- 
culus Eschscholtz) at Waimanalo Beach, Oahu, 
during the high surf of June, 1954. However, 
these sand crabs completely ignored another 
colonial hydrozoan, Velella pacifica Esch- 
scholtz, present in the surf at the time. Viewing 
these two colonial hydrozoans from above, as- 
tute man could easily differentiate between the 
gas filled float of Physalia and the flattened, 
elliptical float and oblique sail of Velella , but 
less sagacious sand crabs, viewing these colo- 
nial hydrozoans from below, could not be 
expected to discern subtle differences of color 
or length of suspended zooids. This would 
be especially true during a high surf because 
of increased turbidity, yet, in no instance did 
I observe even a tentative approach to Velella . 
Even though H. pacifica has well developed 
eyes, the likelihood that selection of Physalia 
and rejection of Velella could result solely 
from visual discrimination is unlikely. 
Whereas unselective feeding by antennal 
straining has been investigated' in Emerita , 
insofar as could be ascertained, no published 
work on selective feeding in H . pacifica has 
been reported. Therefore the experiments re- 
ported on here were performed to investigate 
the method by which selective feeding is 
accomplished. 
1 Contribution No. 69, Hawaii Marine Laboratory. 
2 Department of Zoology and Entomology, Uni- 
versity of Hawaii. 
My appreciation is extended to Dr. Max- 
well Doty, University of Hawaii, for the phy- 
cological determinations and to Dr. Fenner 
Chace, Jr., United States National Museum, 
for the identification of the Hawaiian sand 
crabs. 
METHODS AND TECHNIQUES 
A. Sand crabs collected during the high 
surf were usually attached (singly or in groups 
of five or six) to their captured Physalia. These 
crabs were removed and taken immediately 
to the laboratory where antennae, antennules 
and the contents of the dissected digestive 
systems were examined microscopically for 
the presence of minute plants and animals 
(exclusive of bacteria), an abundance of which 
would indicate unselective, filter feeding. 
B. Physalia and Velella disappeared from the 
surf as the wind subsided but, washed high 
on the beach, stranded colonies formed an 
almost unbroken line as evidence of their 
previous abundance in the sea. These served 
as a ready source of food for subsequent ex- 
periments. Sand crabs likewise disappeared 
from the surf as the sea calmed, leaving the 
wave-washed region of the beach bare. Upon 
this region of the beach I tossed (1) pieces of 
algae ( Ulva fasciata Delile, Turbinaria ornata 
J. Agardh, Sargassum ohtusi folium J. Agardh, 
Polyopes clarionensis Sethchell & Gardner) bro- 
ken to approximately the size of Physalia ; 
(2) Velella; (3) pieces of commercial shrimp 
discarded by fishermen; and (4) Physalia. 
Sand crabs which responded to any of these 
materials were collected and taken to the 
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