A preliminary account of the general and enzyme histochemistry of Siboglinum atlanticum and other Pogonophora.
Southward, E.C. and Southward, A.J. (1966) A preliminary account of the general and enzyme histochemistry of Siboglinum atlanticum and other Pogonophora. Journal of the Marine Biological Association of the United Kingdom, 46 (3). pp. 579-616.
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An account is given of the distribution of certain polysaccharides, lipids and proteins in the tissues of Siboglinum atlanticum, a uni-tentaculate pogonophore collected from depths of 13°0-15°° m on the continental slope. The histology of the various glands and cells is described, and the structure and histochemistry of the tentacle compared with that of three multitentaculate species of pogonophores collected from similar habitats. Esterases hydrolysing a-naphthyl acetate and o-acetyl-bromoindoxyl are found in most tissues of Siboglinum after formalin fixation. An eserine-sensitive esterasewas present in the dorsal ciliated band, mostly close to the bases of the cilia. An organophosphorus-resistant esterase was widely distributed as scattered particles in the subcuticular region of the epidermis of the tentacle and anterior end. The other tissues, including the epidermal glands, blood vessels, muscles and peritoneum, contained a simple B-esterase which was closely associated with lipid globules; the nerve fibre B-esterase was not associated with lipid and its apparent sensitivity to copper illustrates one aspect of the difficulty of applying mammalian esterase subdivisions to invertebrates. Lipids form the main food reserve, and appear to have a dominant role in the metabolism. Pogonophores do not possess a gut at any stage in their life, and must take up food through the epidermis, whether or not it is first digested. The epidermal glands do not appear to have any digestive function. The multicellular pyriform glands secrete fibres of chitin and acid mucopolysaccharide, and produce the major part of the tube in which the animal lives. The unicellular glands are of several types, but most of them, apart from some simple mucous glands, appear to take part in tube formation, secreting mucopolysaccharides or mucopolysaccharides and protein. Secretory cells similar to those producing digestive enzymes in other invertebrates could not be found anywhere in Siboglinum. Protease activity could not be demonstrated on whole live specimens or on extracts using a gelatin-silver method, and tests on fixed material for arylamidase were negative. The apparent absence of protease and alkaline phosphatase, and also of dehydrogenase according to Manwell, Southward & Southward (1966), may, however, be due to the instability of these enzymes at temperatures higher than in the normal habitat (5-7° C) or to very critical incubation requirements. The tentacle is well fitted for respiratory exchange, but must also function in uptake of food. In the absence of digestive processes comparable to those taking place inside a gut, it is presumed that Siboglinum, and probably other pogonophores, absorb soluble organic matter from the environment. The electron microscope observations of Gupta, Little & Philips (1966) supplemented by our histochemical results indicate that the cuticle is a living structure comparable to the brush border of intestinal epithelia and to the integument of intestinal parasites. Pogonophores may therefore be capable of active uptake against a concentration gradient, by adsorption on to a layer of finely structured mucopolysaccharides and subsequent pinocytosis. The subcuticular esterase may be part of the enzyme system involved in this process.
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