Fluted kidneyshell: Ptychobranchus subtentum

Kidneyshells are "fly fishermen".  The glochidia are enclosed in membranous capsules (ovisacs) that are remarkably decorated to mimic host prey items.  In the fluted kidneyshell, the ovisacs resemble aquatic insects, particularly the pupae of blackflies (Simulidae).   Each ovisac has a transparent, adhesive "tail", which tethers it to objects on the stream bed after release from the female mussel.  Water movements cause the ovisac to move, attracting the host fish (primarily darters).  When a fish bites the ovisac, glochidia are forced out through the "eyes", or are released by rupture of the ovisac, and then attach to the gills of the host.

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Ptychobranchus subtentum (fluted kidneyshell) from the Clinch River, collected by Jim Layzer. This individual released over 200 ovisacs. The ovisacs of fluted kidneyshell   resemble aquatic insects. Each ovisac is roughly 2 cm long, of which about 2/3 is "tail".
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The transparent "tail" is adhesive and highly elastic. The filaments that project from the ovisac "head" are actually pigmented streaks within a clear matrix. The ovisacs resemble blackfly pupae, which bear filamentous cephalic respiratory appendages. Complex details of coloration may be necessary to fool discriminating host fish (darters).
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Each ovisac is a bag of several hundred glochidia The "eyes" are zones of weakness that tend to rupture. Note the glochidium lying near the "eye" opening Each glochidium is about 220 micrometers long

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