Epizoic bacteria on the foot of the Antarctic bivalve, Lissarca notorcadensis Melville and Standen, 1907 (Filibranchia: Philobryidae) |
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Authors: | Hans Heinrich Janssen |
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Institution: | Projektgruppe Elbe-?kologie in der Bundesanstalt für Gew?sserkunde, Schnellerstrasse 140, D-12439 Berlin, Germany Fax: 030-63986-439, DE
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Abstract: | Specimens of the epizoic bivalve Lissarca notorcadensis Melville and Standen, 1907 (Philobryidae) were collected from the spines of cidaroid sea-urchins in the Weddell Sea during
austral summer 1991. Soft tissues were investigated by means of transmission electron microscopy. Epizoic bacteria were discovered
on the foot in 14 out of 15 specimens of the bivalve, and in juveniles as well as in adults. The presence of bacteria was
restricted to a certain area of the foot's surface, where they were populating the brushborder of the epidermal epithelium.
This is the first time that epizoic bacteria have been described, either from an Antarctic bivalve or from the foot epithelium
of any bivalve species. Aspects of the fine structure were studied with regard to future work on this symbiosis. The bacteria
undergo a full life-cycle in the brushborder. Whereas young or dividing bacteria are found more distally between the microvilli,
senescent stages seem to disintegrate and be absorbed between their bases. The bacteria could contribute to the nutrition
of their host by breaking down macromolecular or particulate organic matter, which would facilitate parenteral absorption
by the bivalve, as well as eventual digestion. The ultrastructural findings suggest that the bacteria are neither sulphidotrophic
nor methylotrophic. Based on their appearance, they are classified as sub-cuticular bacteria, which have been recently described
from the surface epithelia in various marine invertebrate species. The phenomenon is discussed in respect to seasonal food
limitation for Antarctic suspension feeders and the brooding behaviour of the host species and its ecological success.
Received: 26 April 1996 / Accepted: 8 September 1996 |
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