Trapezia and Tetralia Ectoparasites — Knudsen 
of crabs) was placed in another bucket. This 
process was completed swiftly so as to prevent 
crab movement from one part of the head to 
another. Both the live and dead portions of 
coral included specimens of Trapezia. 
Thus, Experiments 3, 4, and 5 suggest that 
Trapezia will dwell in dead Pocilloporidae only 
if a live portion is present, again suggesting 
that live corals are essential for the commensal 
relationship. Furthermore, totally live heads of 
Pocilloporidae (Experiment 6, station 63) 
yielded 17 species of crabs including 5 species 
of Trapezia, as would be expected from Garth’s 
account and from the control results of Experi- 
ments 1 and 2. 
Acroporid and pocilloporid coral heads are 
often found side by side in a given habitat, to- 
gether with their commensals, Tetralia and 
Trapezia, respectively. The very low incidence 
of mismatched crabs and corals recorded at the 
time of our experimentation (one record of 
Tetralia on a pocilloporid coral, Garth, 1964: 
142) prompted further field studies to deter- 
mine if these crab genera display a true specific- 
ity for their coral families. Live acroporid and 
pocilloporid corals were collected (Experiment 
7), their crabs were exchanged ( Tetralia placed 
on Pocilloporidae and Trapezia on Acropori- 
dae), and then were placed back in the deep 
reef pool. After 3 days the crabs were absent, 
suggesting that a true specificity does exist. 
The feeding habits of the Trapeziinae were 
checked in the laboratory on captive animals 
used in reproductive studies. Attempts to serve 
as food either cut fish or algae proved unsuccess- 
ful for maintaining breeding animals. Brine 
shrimp {Artemi a) nauplii were offered to the 
crabs with only apparent good results. Experi- 
mentally, however, crabs were starved 3 days 
in clean aquaria (Experiment 8) and then of- 
fered tremendous numbers of live Artemi a 
nauplii for filter feeding. Half of these crabs 
were fed at night, the other half during the 
daytime. After a suitable feeding period had 
passed, the crabs were killed and the stomach 
contents examined. In no instance could Artemia 
nauplii, or their fragments, or other plankton, 
be recognized. On the other hand, Artemia eggs, 
which happened to be introduced with the 
nauplii and which sank to the bottom of the 
aquaria, were found in the stomachs of two 
53 
specimens of Trapezia . These experiments indi- 
cate that normal filtered food, meat baits, and 
algae are not the normal diet of the Trapeziinae. 
Next (Experiment 9), crabs were collected in 
the field from their coral hosts, killed by cutting 
the carapace (to insure quick preservation), 
and dropped into solutions of 5% formalin or 
75% alcohol. Under microscopic examination 
(430 diameters), without stain, no specimens 
of phytoplankton or zooplankton could be recog- 
nized. Instead, small round globules of some 
sort were present in the stomachs. This material 
was not identified or classified. 
Concurrently, a series of laboratory experi- 
ments (Experiments 10-13) were initiated to 
gain better insight into the possible host-speci- 
ficity exhibited by the Trapeziinae, and to 
determine the nature of their feeding habits. 
For Experiment 10, two aquaria measuring 
10 by 24 inches, by 18 inches deep, were set 
up and supplied with running seawater. Each 
tank was devoid of foreign material but was 
provided with one live pocilloporid head with 
three Tetralia and one live acroporid head with 
three Trapezia (these crabs were switched from 
their "preferred hosts"). The two coral heads 
in each aquarium were placed about 10 inches 
apart. After 24 hours the collective results from 
the two tanks showed that three Tetralia had 
migrated to acroporid coral, one remained on 
a pocilloporid coral, one was dead and the last 
was missing; all six of the Trapezia had moved 
to pocilloporid corals. This experiment demon- 
strated a distinct preference on the part of these 
crabs to seek out their preferred host coral. The 
data are not conclusive, but may suggest that 
this preference is slightly stronger in the 
Trapezia genus. 
Experiment 11 utilized two identical running- 
seawater aquaria devoid of all foreign material. 
A small head of acroporid coral with five 
Trapezia was placed in one tank, while a pocil- 
loporid coral with five Tetralia was placed in 
the second tank. No other corals were available 
to these crabs. After 24 hours five Trapezia 
remained on the acroporid coral (although one 
was dead) ; four Tetralia remained on the pocil- 
loporid coral while a fifth crab (dead) was 
found a few inches away. These results tend 
to suggest that physical protection was sought 
here in the "wrong" coral since the proper 
