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Endosymbiotic bacteria in the hot-vent gastropod Lurifax vitreus (Heterobranchia: Orbitestellidae)

Abstracts of the 18th WCM, Ponta Delgada, Portugal [A.M. de Frias Martins, A.C. Costa, R.T. da Cunha, S. Ávila, S.C. Monteiro & P. Raposeiro, (eds)]. Açoreana Suppl. 8: 76

Authors/Editors: Hawe A
Gensler H
Haszprunar G
Publication Date: 2013
Type of Publication: Congress Contributions and Posters

Molluscs of chemosynthetic habitats (e.g. hot-vents, cold seeps, whale or wood falls) frequently harbor ecto- or endosymbiotic bacteria, which use hydrogen sulfide or methane as energy source. Such bacterial symbionts may substantially contribute to the energy metabolism of the host. Among the Gastropoda so-called “bacteriocytes” (tissues with intracellular bacteria) have been demonstrated in certain taxa of Neomphalida, Veti- or Caenogastropoda, but not yet in higher gastropods (Heterobranchia).

As part of our studies on basal heterobranch families we also examined the Orbitestellidae on the basis of semi-thin section series and computer-aided 3D-reconstructions. We noticed an atypical “granular-glandular” epithelium in the posterior mantle cavity within Lurifax vitreus. We examined this special epithelium thereafter by means of ultra-thin sections and TEM.

Despite the poor fixation (70% ethanol) we could provide first evidence of an epithelium consisting entirely of true bacteriocytes within basal Heterobranchia. Within the vacuoles of the bacteriocytes we found two morphotypes of probable gram+ bacteria (thick cell membrane and a filamentous electron-dense center). We also could depict various stages of cleavage. Although distinct digestive vacuoles were not found, we detected bacteria in various stages of degradation.

The position of the prominent epithelium with the bacteriocytes in the posterior mantle cavity is so far unique: All hitherto known endosymbiotic bacteria within Gastropoda were found either in ctenidia (Neomphalidae, Peltospiridae, Provannidae) or directly associated with the gut (Bathyphytophilidae) or spread in the haemocoel (Lepetellidae). In contrast, a parallel case might exist in the monoplacophoran Laevipilina antarctica with likewise pallially situated bacteriocytes. Future studies on other genera of Orbitestellidae should clear up, whether the bacteriocyte system is restricted to hot-vent inhabitants or more wide-spread in the family.

 

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