Gill Morphology and Terrestrial Adaptation in the Estuarine Crab Uca Uruguayensis Nobili, 1901 (Decapoda, Brachyura)

Abstract

[Gill area (GA), proportion of ion-regulation and respiratory tissue surface, mean thickness of diffusion barrier (epithelium plus cuticle) and metabolic rate/gill area ratio (VO 2 /GA) were measured in the intertidal fiddler crab Uca uruguayensis. Mean GA was 351.56 mm 2 ± 19.55, n = 18, 60% corresponding to ion-regulation tissue surface and 40% to respiratory area. Mean diffusion distance was 8.02 μm, ranging from 1.63 μm at the fourth gill pair (fully respiratory) to 12.0 μm for the seventh, ion-regulatory, gill pair. Cuticle thickness was 0.81 μm in the lamellae of all the gills; a thicker cuticle was noted in the marginal channels (up to 10 μm), that provide structural support to the gills. VO 2 /GA was calculated for U. uruguayensis and compared with the same ratio for several species living in different habitats. This ratio increased with terrestrial tendencies, being sevenfold higher in terrestrial crabs than in aquatic and low tide ones. Air-active intertidal species, like U. uruguayensis showed intermediate values between those groups., Gill area (GA), proportion of ion-regulation and respiratory tissue surface, mean thickness of diffusion barrier (epithelium plus cuticle) and metabolic rate/gill area ratio (VO 2 /GA) were measured in the intertidal fiddler crab Uca uruguayensis. Mean GA was 351.56 mm 2 ± 19.55, n = 18, 60% corresponding to ion-regulation tissue surface and 40% to respiratory area. Mean diffusion distance was 8.02 μm, ranging from 1.63 μm at the fourth gill pair (fully respiratory) to 12.0 μm for the seventh, ion-regulatory, gill pair. Cuticle thickness was 0.81 μm in the lamellae of all the gills; a thicker cuticle was noted in the marginal channels (up to 10 μm), that provide structural support to the gills. VO 2 /GA was calculated for U. uruguayensis and compared with the same ratio for several species living in different habitats. This ratio increased with terrestrial tendencies, being sevenfold higher in terrestrial crabs than in aquatic and low tide ones. Air-active intertidal species, like U. uruguayensis showed intermediate values between those groups.]