HISTOLOGICAL, HISTOCHEMICAL, AND ULTRASTRUCTURAL INVESTIGATIONS ON THE GASTROINTESTINAL SYSTEM OF ANTARCTIC SEALS - WEDDELL SEAL (LEPTONYCHOTES WEDDELLII) AND CRAB-EATER SEAL (LOBODON CARCINOPHAGUS)

The morphology of the principal sections of the gastrointestinal syste m of two Antarctic seals with different dietary habits, namely, the We ddell seal (Leptonychotes weddellii) and the crabeater seal (Lobodon c arcinophagus), has been investigated. Histologically examined by light microscopy, the tissue layers of the gastrointestinal tract of both s eals are almost identical to those observed in most other mammals and no major differences in principle organization could be found between the two seal species. The ultrastructure of the gastric and intestinal epithelial cells has been examined and is also closely comparable to that of these cells in other mammals; however, Paneth cells have not b een found in our material. In general, therefore, adaptations of the g astrointestinal tract to the aquatic environment or the diet are not o bvious at the morphological levels of organization studied. Histochemi cal differences are found between the two closely related species; muc ins of the surface epithelium in the stomach of Weddell seals are high ly sulfated, while those in the crabeater seal are not. Mucous neck ce lls in Weddell seals contain acid mucosubstances, while those of crabe ater seals contain neutral ones, Goblet cells in the small and large i ntestine in Weddell seals contain both neutral and acid mucosubstances . Both mucin types are detected in the crabeater seal; however, the mu cins of the colon in the crabeater seal are more highly sulfated than those in the Weddell seal. The ratio of goblet cells to enterocytes in the large intestine of crabeater seals is higher than that in Weddell seals. (C) 1995 Wiley-Liss, Inc.