Fig. 216.—The Thornback Crab (Maia Squinado)
Closely allied to the last-named, and belonging to the same family, is the well-known Thornback Crab (Maia Squinado), also a very common crab, of which we give a separate illustration.
The tribe Catametopa does not contain many British species, the principal being the Pea Crabs; the Floating Crab, which is occasionally washed on the south-west coast; and the beautiful Angular Crab. In these the front of the carapace is turned downwards—a feature that has suggested the name of the tribe.
Fig. 217.—The Pea Crab (Pinnotheres pisum)
The pea crabs are all small, and they are parasites, living within the shells of bivalve molluscs. One species—the Common Pea Crab (Pinnotheres pisum) is frequently found in the Edible Mussel; the female, which is much larger than the male, being much more commonly found. Another species—the Pinna Pea Crab (P. veterum), infests the Pinna and Modiolus.
On [Plate VI.] is a drawing of the Angular Crab (Gonoplax angulata) mentioned above, the striking form and delicate colouring of which can never be mistaken. We would, however, call particular attention to the broad and square front of the cephalothorax, with its two sharp spines, and to the length of the eye-stalks. Unfortunately for the amateur, this pretty crab is only to be found in deep water, off the coasts of Devon and Cornwall, so that here, again, the aid of the fisherman is valuable; but, as observed in the case of other deep-sea dwellers, may also be looked for in the stomachs of cod and other bottom fishes. The sex figured is the male, in which, when fully grown, the front legs are much longer than in the female.