Kath, After following the discussion for the last few days I have to agree with most of your points. I have also collected extensively in the Pacific and have seen this type of wear on many different genera, especially Nerites and Turbinids but also Muricids like Chicoreus and Thais and I think maybe Cerithium too. The damage is mainly around the columella but can involve the aperture too. I have also seen holes in these shells adjacent to the suture lines and which appear to me to result from thining of the shell in this region - although not often. Not infrequently there is minimal wear externally, so I cannnot accept beach rolling as a mechanism. I also note that I have only seen this in tropical areas and probably only with terrestrial hermits. I could not vouch for intertidal species but I cannot recall ever seeing this on a dived shell. Here in Victoria Australia our species are all marine and I have not seen this sort of wear either - even in shells with large Calyptrea coinhabiting in tha aperture. I wonder if chemical is likely as the columella would be in constant contact with the soft parts of the crab and these always seem a little moist when one is extracted. With constant moisture, a little acid and some light abrasion the dissolution of the CaCO3 could possibly be quite rapid. On the side of abrasion, Someone mentioned that the crabs claw grows to fit the aperture. Do we know this is the case or is the aperture abraded also by the claw? It is interesting to note how snugly the claw fits in place. Geoff Macaulay >From: Katherine Szabo <[log in to unmask]> >Reply-To: Conchologists of America List <[log in to unmask]> >To: [log in to unmask] >Subject: In defence of hermit crabs >Date: Fri, 12 Oct 2001 13:52:31 +1300 > >Hi everyone and thanks for all the responses: > >There appear to be many unbelievers that hermit crabs damage the shells >they >live in. I too have collected many specimens occupied by hermit crabs >while >in the Pacific and many do not display damage - maybe damage is time and >taxa related. Let me use Neritidae as an example. In my experience (and >in >many of my archaeological samples) the edges of the aperture have been >dissolved; ie the columellar pad has been partially etched or abraded away >as well as any denticles on the opposite side of the aperture. It is in >this way that the aperture is widened without literally breaking the >aperture or chipping it back. This is certainly not the doing of the >mollusc and seems an unlikely wear pattern in relation to beachrolling and >other intertidal action. I can only tie it sensibly to hermit crabs. >Although most obvious often in Neritidae, similar damage is often seen in >Planaxis sulcatus, various thaids and turbinids etc. > With regards to the columella, it is frequently absent, or present only >in remnant form in specimens that have the greatest degree of aperture >damage. This also is clearly not caused by the mollusc and the absence of >a >columella when the rest of the shell is largely in tact is an odd thing >indeed - though very common in the samples I look at. > Hermit crabs are the only feasible explanation I can see to explain this >sort of damage - though perhaps terrestrial rather than intertidal hermit >crabs (?). This sort of damage has been reported in relation to Coenobita >rugosus (Carucci 1992; Kinosita and Okajima 1968:296). > >Have I been vindicated for my choice of indicators? > >Kath. > > > ><br><br><br><html><DIV>Katherine Szabo </DIV>Archaeology and Natural >History ><DIV></DIV>Research School of Pacific and Asian Studies ><DIV></DIV>Australian National University ><DIV></DIV> ><DIV></DIV>Canberra ACT 0200 ><DIV></DIV>Australia ><DIV></DIV>Ph:61-2-6125 2235 ><DIV></DIV></html> > > >_________________________________________________________________ >Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp _________________________________________________________________ Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp