>  Environments similar to these vents may originally been the
>  startingpoint for life, but molluscs weren't around then, and i very
>  much doubt that they originated there. So the presence of "primitive"
>  molluscs on the smokers is purely coincidental.

Although there's no evidence that the Mollusca originated in hot-vent like habitats, the extreme stability of these habitat types over geologic time may favor the survival of anything that figures out how to live there.  Thus, any type of mollusk that successfully invaded the hot vent habitat back in the Paleozoic may have been able to hold on in that habitat while the more competitive and more fluctuating shallow water habitats underwent more turnover.  On the other hand, there seem to be some extinct Paleozoic hot-vent mollusk higher taxa.

>  Work needs to be done, probably, on the metabolisms of all of the
>  vent fauna... I don't doubt that some of the species there are not
>  chemosynthetic, but merely feed on available foodsources there
>  because just because they are available. The toxicity of the
>  environment and the chemosynthetic organisms, as well as of those
>  organisms feeding on the chemosynthetic bacteria etc, is one possible
>  reason for the apparent paucity of predatory gastropods around the
>  vents.

In particular, chemosymbiotic mollusks need to devise ways to supply their symbiotic bacteria with hydrogen sulfide without poisoning themselves with it.  Lucines have developed a modified anatomy in which the elongate anterior adductor forms a barrier between the oxygenated water that the clam needs for respiration and the anoxic, sulfide-rich water that the bacteria need.

Lucines also exemplify a good way to invade hot vent habitats.  Anoxic sediments have vaguely similar chemistry, though without the high temperatures.  Once you're good at dealing with those habitats, you may be able to take on the vents.

    Dr. David Campbell
    Old Seashells
    University of Alabama
    Biodiversity & Systematics
    Dept. Biological Sciences
    Box 870345
    Tuscaloosa, AL  35487-0345 USA
    [log in to unmask]

That is Uncle Joe, taken in the masonic regalia of a Grand Exalted Periwinkle of the Mystic Order of Whelks-P.G. Wodehouse, Romance at Droitgate Spa

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