ABSTRACT
The air-breathing mangrove crab Goniopsis cruentata ventilates the branchial chambers with its scaphognathites (SG). Ventilation is predominantly in the forward direction, but is punctuated by bouts of reversed pumping. Reversals are more frequent when crabs are in air than in water, and yet more frequent during respiratory stress (hypoxia or exercise). Reversed SG pumping is tightly coupled with bursts of impulses to the dorsal-ventral muscles (DVM) which span the anterolateral thorax. Phasic contractions of the DVMs increase the hemolymph pressure in the dorsal sinuses. These pressure pulses help drive hemolymph through the lungs. The coupled SG reversed ventilation and DVM-assisted increases in lung perfusion appear to be an adaptation to increase gas exchange at the lungs.
When crabs are made hyper-or hypotensive by changes in hemolymph volume, the EMG activity of the DVMs dramatically decreases or increases, respectively. The resultant expansion or constriction of the dorsal sinuses is an effective baroreceptor reflex producing short-term adjustments in hemolymph pressure.
