Chromatophore Responses in Relation to the Photoperiod and 
Background Color in the Hawaiian Ghost Crab, 
Ocypode cerato phthalma (Pallas ) 1 
Georgiandra Little 2 
The functional activities of chromato- 
phores are classified as morphological when 
there is a change in the amount of pigment 
present over a period of time, and as physiolog- 
ical when there is a relatively rapid change due 
to changes in the degree of dispersion of the 
pigment. A primary chromatophore response 
is a response to a nonvisual stimulus, while a 
secondary response is a response to a visual 
stimulus (Fingerman, 1963:8). 
The most common method of describing the 
degree of dispersion of the chromatophore pig- 
ments is that of Hogben and Slome (1931:12, 
fig. 1) using a one to five scale, where one 
corresponds to maximum concentration and five 
to maximum dispersion of the pigments, and 
the intermediate stages are described as two, 
three, and four. 
The present study deals with the ability of 
the Hawaiian ghost crab, Ocypode ceratoph- 
thalma (Pallas), to maintain a rhythmic physio- 
logical chromatophore response with different 
periods of light and darkness and on different 
backgrounds. 
The author wishes to thank Dr. Ernst Reese 
at the University of Hawaii and Dr. John D. 
Costlow, Jr. and Dr. Edward C. Horn at Duke 
University for their kind assistance and many 
helpful suggestions. 
MATERIALS AND METHODS 
Male and female ghost crabs were collected 
from three different areas on the island of Oahu, 
where the beaches are composed of very fine 
1 This work was supported in part by an award 
granted to the Department of Zoology, Duke Uni- 
versity by the National Science Foundation Under- 
graduate Science Education Program (G-21879). 
Manuscript received December 1, 1965. 
2 Department of Zoology, Duke University, Dur- 
ham, North Carolina. 
sand presenting a white background. Large 
crabs, with a carapace length of more than 22 
mm, and medium crabs, with a carapace length 
of less than 22 mm, were collected. A length 
of 22 mm was chosen as the dividing point be- 
tween large and medium crabs because ghost 
crabs begin to develop eye stiles, a characteris- 
tic of mature crabs, when they reach a carapace 
length of more than about 20 mm (Crane, 
1941:303). Several attempts were made to use 
small crabs with a carapace length of less than 
12 mm, but these tiny crabs almost always died 
within 18 hr, making any prolonged experimen- 
tation impossible. Since no apparent difference 
was observed in the chromatophore responses of 
the two crab sizes, the results have been com- 
bined. 
Crabs were caught either at night or shortly 
after dawn by chasing them with nets or by 
digging them out of their burrows. They were 
placed immediately in individual 8X4x4 inch 
plywood boxes with y 2 inch mesh wire tops, 
filled about % inch deep with sand. These crabs 
were returned to the laboratory within an hour 
after collection, and a petri dish of sea water 
was put in each box. 
Within 8 hr after return to the laboratory the 
crabs were placed on one of the following 
regimes. 
White background, normal photoperiod 
White background, reversed photoperiod 
White background, constant darkness 
White background, constant illumination 
Black background, normal photoperiod 
Black background, reversed photoperiod 
Black background, constant darkness 
Black background, constant illumination 
During an experiment the animals’ black 
chromatophores on the proximal, anterior sur- 
face of the third walking leg were indexed, 
using the Hogben and Slome (1931) indexing 
77 
