A COMPARATIVE STUDY OF THE GILL AREA OF CRABS I. E. GRAY Department of Zoology, Duke University, Durham, N. C. In a comparative study of the gill area of marine fishes (Gray, 1954), it was shown that a definite correlation exists between the size of the gill area, the degree of activity, and the habits of the fishes concerned. It was found that sluggish bot-tom-dwelling species have proportionately much less gill surface than do fast swim-ming pelagic fishes. In this paper an attempt is made to find out if similar corre-lations exist in crabs from different habitats. Several correlations pertinent to the present discussion have already been pointed out by others. Ayers (1938) indi-cated that intertidal and land crabs consumed oxygen at a higher rate than did the strictly aquatic species. Pearse (1929a, 1929b, 1950) in his study of the emi-gration of animals from the sea has reported that there is a lessening of gill volume as crabs emigrate toward land. Pearse determined only the gill volume, not the gill area. More recently Vernberg (1956) has shown in a series of crabs that oxygen consumption of the whole animal and of gill tissue is highest in terrestrial species and decreases progressively as the habitat approaches ocean depths. This paper presents the results of a study of the gill areas of sixteen species of brachyuran crabs from six taxonomic families, and representing both pelagic and benthic species, and those living below the low tide level, those of the intertidal zone, and those that live out of water most of the time. Grateful acknowledgment is made to the Duke University Research Council for partial support of this research and to Miss Darlene Connor and Miss Barbara Galloway for the technical assistance. MATERIALS AND METHODS The method used in the determination of gill area in crabs was similar to that employed in the determination of gill area in fishes (Gray, 1954). With crabs, however, since the gill platelets are so much larger, the procedure is somewhat less tedious. Each crab was weighed after first removing surplus water from the body and gill chambers with paper toweling. The gills were then removed from one side and each placed in a separate Petri dish. The total number of platelets for each gill was counted under a dissecting microscope or computed after measuring the length of each gill with vernier calipers and determining the average number of platelets per millimeter of length. After preliminary trials to observe the range of sizes, what appeared to be average size platelets from each gill were removed and mounted in sea water on slides. Using a dissecting microscope, camera lucida drawings were made of the selected platelets and the area of these determined by means of a planimeter. Knowing the magnification used and the total number of platelets, the total gill area could be readily calculated. A weak point in the pro-34
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