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The oburaculum of Riftia pachyptila (Annelida, Vestimentifera): ultrastructure and function of the obturacular muscles and extracellular matrix
Andersen, A.C.; Hamraoui, L.; Zaoui, D. (2001). The oburaculum of Riftia pachyptila (Annelida, Vestimentifera): ultrastructure and function of the obturacular muscles and extracellular matrix. Cah. Biol. Mar. 42(3): 219-237
In: Cahiers de Biologie Marine. Station Biologique de Roscoff: Paris. ISSN 0007-9723, more
Peer reviewed article  

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Keyword
    Marine

Authors  Top 
  • Andersen, A.C.
  • Hamraoui, L.
  • Zaoui, D.

Abstract
    The Vestimentifera have in their branchial plume a centralized structure, the obturaculum, supporting the respiratory lamellae and enabling the worm to close its tube. We have studied its structure in Riftia pachyptila, focusing on the relations between its main parts: epidermis, muscles and extracellular matrix (ECM). The epidermis is supported by a thick collagenous layer, through which cell processes extend into the ECM. These processes contain rough endoplasmic reticulum (RER), and they often surround the subepidermal obturacular muscles. Each muscle is a bundle of 10-35 smooth muscle fibres, embedded in the ECM. The apical part, made of thin (and probably juvenile) muscle fibres, is present in each muscle. The thick myofilaments range from 20 to 150 nm in diameter, and show a cross-banded periodicity of 12-14 nm similar to paramyosin. Each thick myofilament is surrounded by 12 to 18 thin myofilaments about 5-7 nm in diameter. The nucleus is located laterally in the fibres, and generally surrounded by swollen cisterns of RER. The large obturacular matrix contains collagen fibrils, with a diameter of 30 nm and a striation every 64 nm. It also contains proteoglycans and cells, in groups of two or more, surrounded by a thin basal lamina, often lined with bundles of collagen fibrils. These cells often contain swollen cisterns of RER, suggesting they are equivalent to fibroblasts synthesizing the surrounding collagen fibrils. We discuss whether the obturaculum presents the features of a primitive cartilage, or those of a " catch " type connective tissue.

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