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Shillito. B. (1), Ravaux, J. (1), Menard, F. (1), Goffinet, G. (2), Childress, J.J. (3), Thiebaut, E. (1), Delachambre, J.
(1), Gaill, F. (1)
I INSU CNRS Roscoff, UPMC, 7 Quai Saint Bernard, 75252 Paris, France 2 Institut de Zoologie, Universite de Liege, 22, Quai Van Beneden, B-4020 Liege, Belgium. 3 Department of Biological Sciences and Marine Science Institute, University of California, Santa Barbara, California, 93106, USA.
Summary: Tube growth rate and process were investigated in the case of the hydrothermal vent vestimentiferan Riftia pachyptila. Morphological aspects of worms and their tubes were studied. In parallel, tube production experiments were performed on live animals, in pressurized aquaria. Dry weights of the secretions, along with their chitin content (a major component of the tube) were used to quantify tube produchon. Our results show a variation of the gross morphology of the plume and the trunk of R. pachyptila during its growth and indicate that vestimentum length and tube diameter could be useful indices of individual and tube sizes of R. pachyptila. The presence of basal partitions of freshly secreted tube material at the base of the exoskeleton, as well as observation of branched (bifid) tubes, allow us to propose a model of tube growth at both extremities. In this model the tube growth would exhibit a moulting-like step. Bifid shapes may help in space displacement, and the modification of the positioning in height (by synthesis of basal partitions) may be used by an individual to modify its access to vent fluid.
Ultrastructural observations of the chitin secretion system of this animal, as well as fresh tube material deposits (experiments on live animals) confirm that tube growth occurs at both ends. The experiments performed on repressurized worms indicate that tube production may be extremely rapid, perhaps as an instantaneous response to stressful conditions. When compared to other marine ecosystems, it is obvious that chitin production of the vent communities, based on Riftia pachyptila alone, is the highest recorded and similar values were only reported from polluted freshwater environments.
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