Nutrition chez un invertébré marin détritivore: Leptosynapta galliennei (Holothurioidea: Echinodermata)

Abstract : The definition of some etho-ecological parameters is first given in order to characterize the feeding of Leptosynapta galliennei. The structure and ultrastructure of the L. galliennei digestive tract are fully described. Its wall consists of three tissue layers, a monostratified digestive epithelium, a conjunctive layer, a pseudostratified mesothelium. The latter contains the musculature (epithelial) and is innervated by a plexus (mesothelium). The cell types of the digestive epithelium define five digestive tracts in L. galliennei. These definitions are generalized to other sea cucumbers. The digestive cells appear multifunctional. This is considered to be directly related to the absence of digestive appendages; all functions of nutrition are assumed by the constituents of the digestive epithelium. The relationships between nutritional structures and functions are made from the discovery of hyrolasic potentialities (also studied in Leptosynapta inhaerens and Holothuria forskali) and sites of absorption. Holothurians are characterized by a limited ability to digest proteins. The main site of extracellular digestion is the anterior intestine (weak proteolytic, amylolytic, disaccharidase and lipase activities). There is a correlation between certain enzymatic activities (proteases, amylase) and the presence of a particular type of enterocyte (granular). The low molecular weight elements (dissolved organic matter) are absorbed at the beginning of the tract by cells similar to those of the external epithelium of the integument. These cells, which are associated with subcuticular bacteria, are considered as the morphological support of parenteral absorption. The diet is only partially defined; it can be considered omnivorous. A comparison with annelids indicates that detritivores have different digestive capacities, related not only to the hydrolases present but also to the transit time of the sediment in the tract. The transport of nutrients is mainly ensured by the coelomic fluid. Hemal fluid would have only a marginal role in this function. On the other hand, the hemal system would be a place of cytopoiesis (coelomocytes). Possible reserve sites have been found in L. galliennei (temperate species) and in Eunolpadia violacea (subantarctic species) during their sexual cycle and during a fast. An extragonadic reserve site was not found in either species. Fluctuations in the biochemical composition of the gonad reflect changes in the energy value of adults during the cycle. Short-lived fasting does not cause the depletion of any organ in L. galliennei.
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Contributor : Jean-Pierre Féral <>
Submitted on : Sunday, July 2, 2017 - 7:48:15 PM
Last modification on : Friday, July 5, 2019 - 1:33:59 AM
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  • HAL Id : tel-01552418, version 1

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Jean-Pierre Feral. Nutrition chez un invertébré marin détritivore: Leptosynapta galliennei (Holothurioidea: Echinodermata). Biodiversité et Ecologie. Université Pierre et Marie Curie (Paris VI); Museum national d'histoire naturelle - MNHN PARIS, 1985. Français. ⟨tel-01552418⟩

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