One of the most interesting bivalve defenses I know is utelized by the
Pacific mussel, Mytilus trossulus. Apparently they secrete byssal threads
and literally tie down attacking sea star arms while they make their slow
motion escape (again with byssal threads, sort of slow motion Batman-style.)
I don't know if this is a validated observation, but is commonly mentioned
during SE Alaskan marine bio field trips.
 
I have also heard that the loose periostracum on certain bivalves prevents
sea stars from obtaining a binding grip on the outside of the shell.
Likewise, the radial ribs on bivalves (like cockles) makes a seastar grip
more difficult and prevents a shearing movement between the valves. On the
subject of Cardiids, I would like to know why at least some species (such as
our local Clinocardium nuttallii, Serripes groenlandica, & Serripes
laperousi) feel the need to go "hopping" across the sand when the tide
turns. Locally, at least, the seagulls and ravens have a feast during this
event. It seems kind of counter-productive to me not to wait until the tide
has risen enough to cover the bed. I like to go to one spot locally and wait
for the tide to turn and then take my pick of nice S. groenlandica.
 
I would like to know what defenses certain Leptonaciids (Galeotomacids?)
utelize. One species I know of (Cyamoteia electilis) from west Mexico lives
(at least some times) with the thalassinid shrimp Axiopsis (Family Axiidae.)
If any of you not familiar with Axiid shrimp, they are voracious carnivores.
The bivalves seem to be quite comfortable in the shrimp burrows, often one
can find 5-20 in a single burrow. Cyamoteia, like many of its family
worldwide that share homes with carnivorous crustacea, have a paper-thin
shell and expanded mantle that makes the shell seem almost vestigal. In an
experiment that I kind of regret (I dislike unneccesary cruelty), I dropped
two Cymtoeia into the burrow of a related Axiid, (Neaxius something or
other) and they both were quickly shredded and presumably eaten. I did
notice that the original host shrimp treated the Cyamoteia like the coral
rubble the burrow was composed of in that it would repair the burrow by
stuffing both coral and bivalves into the damaged (by me) walls of the
burrow. I assume that the bivalves have some mechanism to prevent them from
being eaten. Many other members of this family live with crustaceans like
Squilla that are even more bad-temepered than Axiids. Any facts and/or
speculations about how these bivalves mange to survive where they do? The
why is simple, few predators would survive long in the burrows. The how is
problematic. I really look forward to comments on this and Ross' original
post. - Aaron
Aaron Baldwin
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