BIOLOGIYA MORYA, 2017, Vol. 43, No. 6, pp. 413-429 |
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Morphology and microscopical anatomy of the deep-sea echiurid Protobonellia zenkevitchi Murina, 1976 Faculty of Biology, M.V. Lomonosov Moscow State University, Moscow 119234 E-mail: Echiurida is a small group of marine benthic invertebrates burrowing in sediments and living a hidden lifestyle. Investigation into the morphology and anatomical features of various organ systems allows better understanding of biology of these enigmatic animals, many of which are deep-sea species. The morphology and microscopical anatomy of the deep-sea echiurid Protobonellia zenkevitchi Murina, 1976 were studied using the light microscopy and histology methods. The body of P. zenkevitchi is divided into proboscis and trunk. The ciliary grooves and large vacuolated cells in connective tissue of the distal part of proboscis suggest a specific position of the proboscis on the sediment surface and a mechanism for sorting out food particles. It has been shown for the first time that the coelom is not subdivided into compartments. In the digestive tract, there has been found an unusual part of midgut, previously unknown for echiurids, probably performing the function of food storage. This part provides thorough food digestion that is important in the oligotrophic conditions of greater depths. The circulatory system of P. zenkevitchi lacks the neuro-intestinal and ring blood vessels. The oocyte storage chamber of gonoduct has a pore, apparently connecting its cavity with the trunk coelom, but lacks a specialized and well expressed part, the androecium. A comparative analysis of the microscopical anatomy shows that many organ systems (muscular, coelomic, circulatory, excretory, and reproductive) in P. zenkevitchi have simpler organization as compared to those in other echiurids. This can probably be explained by the small body size of P. zenkevitchi and the great depths of its habitat. At the same time, P. zenkevitchi possesses some unique anatomical characteristics related to the features of biology of this deep-sea species. Key words: Echiurida, Annelida, morphology, anatomy. |
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