"In many respects, freshwater pearly mussels look like any other bivalve mollusc, but what sets some of them apart (notably
Lampsilis
spp.) is the
unusual extension of their fleshy mantle that grows beyond
the confines of the protective shell valves to wave around in the
water. This fleshy protuberance
can look astoundingly like a small fish
and this is no coincidence because this fishy appendage is actually a
lure to attract fish so they can be press-ganged into the mussel’s
reproductive strategy. The lure is very convincing. Not only does it
have markings that suggest eyes and skin patterning, but it is even
moved by the mussel in a fish-like way. These details are more than
enough to grab the attention of a real fish that mistakes the lure for a
snack. The fish edges closer and makes a lunge for the fake prey
nipping the membrane of a specialized brood gill the lure is
concealing. This releases the mollusc’s larvae, nasty-looking miniature
versions of the adult, known as glochidia. These larvae are parasitic
and they get drawn under the fish’s gill plates where they latch onto
the blood-rich tissues of the gills..."
Further discussion and more examples
here.
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