The venous system of the terrestrial crab Ocypode cordimanus (Desmarest 1825) with particular reference to the vasculature of the lungs

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Abstract
The respiratory system of Ocypode cordimanus consists of seven pairs of gills, modified for aerial gas exchange, and a single pair of lungs. Each lung is formed from the inner surface of the branchiostegite and the thoracic wall of the branchial chamber. The branchiostegal surface is increased by a fleshy infolding, the branchiostegal shelf, whilst the surface area of the thoracic lung wall is enhanced by a large flaplike fold. The anatomy of the major sinus systems and the vascular supply to the lungs were investigated. Venous hemolymph is supplied to the lungs potentially from all the major body sinuses. The dorsal, ventral, hepatic, and infrabranchial sinuses are all connected anteriorly to the two eye sinuses which distribute hemolymph to the lungs. Each eye sinus gives off five branches to the branchiostegal lung surface and one to the thoracic lung wall. These afferent vessels are highly branched and interdigitate closely with efferent vessels. The two systems are connected by flat lacunae lying just beneath the respiratory epithelium and these are believed to be the site of gas exchange. The efferent vessels empty into two pulmonary veins on each side, one serving the branchiostegal lung wall and the other the thoracic wall. The two vessels on each side fuse before joining the pericardial cavity as a single trunk on each side.