The structure and modification of integumental tissues in Pagurus bernhardus (L.) (Decapoda: Anomura)

The histological structure of cephalothoracic and abdominal integuments has been studied in the hermit crab Pagurus bernhardus (L.). In the branchial region of the carapace, the integument shows a similar structure as described hitherto in a number of other decapod species; there are a thin epicuticle, an exocuticle, and a relatively thick endocuticle, followed by a layer of columnar epithelium and underlying connective tissue. This pattern is repeated on the inner surface of the carapace fold but with generally thinner cuticular layers. Within the connective tissue there are tegumental glands, haemocytes, and some reserve inclusions. The abdominal integument shows a modified cuticle structure which is probably related to its specific function as an adhesive organ attaching the hermit crab to the inner surface of the gastropod shell. The cuticle is uncalcified and it shows deep wrinkles and grooves. Endocuticle and exocuticle are thick and layered whereas the epicuticle is very thin. Large funnel-shaped ducts with secretions occur frequently in the abdominal integument. The cells that are responsible for these secretions are described. The chemical nature of integumental structures has been studied with histochemical tests.