THE BRANCHIAL CHAMBER IN TERRESTRIAL CRABS: A COMPARATIVE STUDY

Abstract

The structure, form and relative growth of the branchial chamber was studied in several species of amphibious crabs that inhabit marine, estuarine and fresh water. A general trend in the solution of the problems of aerial respiration was revealed. Growth of the branchial chamber volume is allometric with respect to the body weight of the crab. Data suggest the existence of three categories of complexity in the form, structure and growth of the branchial chamber of amphibian crabs. A lessening in the chamber''s volume is compensated for by an increment in the lining''s surface and by development of new structures inside the chamber itself. The shape of the gill chamber and the kind of respiratory structures, in addition to the branchiae, are not directly relted to habitat. Histological examination of the gill chamber lining showed that the structure is very similar in its general conformation in all species studied. Species of Pseudothelphusidae from Venezuelan mountain creeks present a perforated structure which, by qualitative tests, proved respiratory and accessory to the gills. This lung is located on the anterolateral angle of the ceiling of the branchial chamber. The lung is also present in species of Pseudothelphusidae from Central and South America, including species from the Antilles. From 14 spp. examined from this family, only a Mexican cave dwelling species, Potamocarcinus mocinoi, did not have this structure. The external area, density of perforations, diameter of perforations, and thickness of the respiratory structure found in Pseudothelphusidae were measured; these parameters appear to change with respect to the size of the animal and the species considered. The lack of data on individual species does not allow a more definite conclusion about the inter-specific variation. The development of additional respiratory structures are interpreted as being a consequence of a set of environmental conditions new to the organisms as they colonize land, not just a response to the need for aerial respiration.