Studies in the Calcium and Phosphorus Metabolism of the Crab, 
Podophthalmus vigil (Fabricius ) 1 
Bryant T. Sather 2 
ABSTRACT: By employing modifications of the molt classification by Drach 
(1939) and Hiatt (1948), it was discovered in laboratory-maintained crabs ( Pod- 
ophthalmus vigil) that a partial desiccation occurred during proecdysis followed 
by a rehydration at the A stages. 
The inorganic and organic content of the carapace, mid-gut gland, gills, and 
muscles were followed during the molt cycle. The carapace had the greatest in- 
organic fluctuations. The mid-gut gland and muscle tended to increase in both 
organic and inorganic matter during premolt, suggesting that these organs may 
serve as reservoirs for these components. 
The calcium and total phosphorus constituents of these organs and of the blood 
were determined at the various molt stages. Fluctuations in the amounts of these 
two elements were observed in all sampled tissues. The storage of calcium in the 
mid-gut gland and muscles during premolt is discussed. Phosphorus was found 
to be stored in the digestive gland during postecdysis but not in proecdysis. The 
muscle also tended to store phosphorus during premolt. 
As P. vigil becomes older, i.e., larger, it is unable to resorb from the exoskeleton 
the same quantity of calcium, but it is able to recalcify the new exoskeleton to the 
same extent as does a smaller crab. 
Calcification and hard tissue formation occurs 
in many forms of life. It is found in bacteria 
(Ennever, 1963; Rizzo, et al., 1963; Greenfield, 
1963), algae (e.g., Porolithon and Halamita ), 
protozoans (Isenberg, et al., 1963; Be and Eric- 
son, 1963), coelenterates, echinoderms, molluscs, 
arthropods, and vertebrates. Generally, the func- 
tion of calcification is to give form, support, 
and protection, and to contribute in ionic homeo- 
stasis (Urist, 1962), but in some instances 
calcification can be considered a pathological 
condition. The calcium complex deposited may 
be in three forms — calcite, aragonite, and 
apatite. The latter is a calcium phosphate 
[Ca 10 (PO 4 ) 6 (OH) 2 ] and the others are cal- 
cium carbonate complexes. Very little phos- 
phorus is found in calcite and aragonite, which 
1 A contribution of the Pacific Biomedical Research 
Center and Contribution No. 259 of the Hawaii 
Institute of Marine Biology, University of Hawaii. 
Manuscript received February 14, 1966. 
2 Pacific Biomedical Research Center, University of 
Hawaii, Honolulu, Hawaii. Present address: Depart- 
ment of Zoology, North Carolina State University, 
Raleigh, North Carolina. 
are generally restricted to the lower phyla. The 
amount of strontium and magnesium, the crys- 
tal structure, and the density of the calcium 
carbonate determine the difference between ara- 
gonite and calcite. The latter has little strontium 
and magnesium present in its hexagonal, less 
dense crystalline structure. Apatite is found in 
vertebrate bone, dentine, cementum, and enamel. 
Regardless of the crystal structure and the phylo- 
genetic group in which it occurs, the process 
of calcification can be considered to be basically 
the same (Travis, i960, 1963), although the 
function may be specifically adapted for dif- 
ferent requirements. 
In crustaceans, molting is necessary in the 
apparent growth process. Thus, considerable 
quantities of calcium and organic constituents 
have to be resorbed from the exoskeleton prior 
to ecdysis, but total resorption is limited to 
certain areas, i.e., the endophragmal skeleton 
and the ecdysial sutures. After resorption (via 
the blood) of these constituents, the organism 
is confronted with an abnormally high concen- 
tration of these substances in its internal fluids 
and the animal must either store or excrete this 
193 
