>The "use" of sculpture may change during the growth of the animal. The
>scales of adult Tridacna may be useless, but may have been very important to
>a 1/2 inch juvenile. Adult scales may simply be a holdover from juvenile ones.
>
>We shouldn't write off all spines as being stick-in-the-mouth defenses
>against fishes. If you look at a lot of the cemented bivalves (Spondylus,
>Chama, Crassadoma, Ostraea, etc), they often have spines or scales. It has
>been suggested that these surfaces collect algae and junk, camouflaging the
>animal. I doubt it, because I don't think their predators locate them by
>sight - they probably "smell/taste" them. I think the camouflage is probably
>coincidental with the real purpose of the spines - to keep drilling
>gastropods at bay. Important if you're not going anywhere for a while.
>
>*  G Thomas Watters               *
 
Surface sculpture on bivalves can be very useful for digging and staying
put.  It would make sense that the sculpture changes with the age (read
size and volume) of the animal.  That would have to happen for the
sculpture to be as effective as the animals shape changed.  At least this
is a proposal I have heard and read about which sounds pretty reasonable to
me.
 
Many sea creatures are reluctant to crawl across stinging anemones,
hydrazoans and corals.  I have seen octopus arms turn black and wither up
from stings.  Does the sting effect other sea life?  Would that make a
snail/octopus/starfish less likely to try to open a bivalve?
 
Maybe they aren't camouflaging their shape but their scent by having all
that stuff on their spines?  Sponges often small and feel nasty (some have
sharp spicules in their outer layer).  Maybe they also give off an odor
that can hide the mollusc scent?
 
Just some thoughts - I would bet spines are pretty useful for lots of reasons.
 
Amy
 
Amy Edwards, Program Coordinator ------ [log in to unmask]
 
Museum of Natural History        --------        phone (706) 542-4137
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