Marked sexual dimorphism in carapace shape and size (A. ventricosa Habitus 1, A. ventricosa Habitus 3). In male anterior region is domed with dorsal margin tapering strongly posteriorly. Posterior margin curves symmetrically from dorsal to ventral margin. Ventral margin slightly concave. In some specimens a clear pattern of striae intercept antero-ventral margin at right-angles. Female carapace bean-shaped, with the dorsal margin curving almost symmetrically both anteriorly and posteriorly. Ventral margin is slightly concave. In both sexes right asymmetrical gland broad opening just above level of the ventral margin (A. ventricosa Habitus 1, A. ventricosa Habitus 3). Left asymmetrical gland opens just ventrally of posterior end of the hinge. Both sexes slim in ventral aspect, carapace breadth being a third or less than the length. Flanks curve almost symmetrically (A. ventricosa Habitus 2, A. ventricosa Habitus 4). The frontal organ in North Eastern Atlantic specimens just longer than limb of the first antenna (A. ventricosa 1, A. ventricosa 3); sometimes terminating in a long tapering point. First antennae bent so spinous seta on the end of the second segment appears to be almost terminal. Sensory setae broad, thin-walled and recurved. A characteristic feature is the unusual length of one of the terminal setae of the sixth limb; it is double the length of the other terminal setae and almost equal to whole limb. The caudal furca carries seven pairs of hook setae.
Müller, 1906 originally described the species. Poulsen, 1969a later attributed the much larger specimens in the Dana Collections to it, but Deevey, 1978a placed them in a new species A. poulseni , designating Poulsen's account as the type description The form occurring in U.K. waters is a little larger than the type description, and so may turn out to be yet another sibling.
Widespread, but never common, in the Indian and Atlantic Oceans (0°-49°N) 1 (R.R.S. Discovery Map).
None designated; status of original material uncertain.
The original material was collected in both the Equatorial Atlantic and Indian Oceans (2°-7°N).