Kidneyshells have one of the most sophisticated glochidia delivery devices known among unionids. The glochidia are enclosed in membranous capsules (ovisacs) which mimic host prey such as larval insects or larval fish. An adhesive "tail" attaches to rocks after release from the female mussel. Water movements cause the ovisac to move, which increases its attractiveness to host fish (primarily darters). When a fish bites the ovisac it ruptures, releasing the glochidia, which attach to the gills of the host.
|The Ouachita kidneyshell is a characteristic upland stream species in rivers on the south and west sides of the Ozark Plateaus. This specimen is from the Spring River in Cherokee County, Kansas.|
|Close-up of gravid gill. The marsupial gills are folded, increasing the length of the gill and number of ovisacs that are produced (Lefevre & Curtis 1912). The ovisacs are released in early spring.|
|The ovisacs of Ptychobranchus occidentalis appear to mimic larval fish- (well... maybe!) The transparent "tail" is elongate and adhesive to attach the ovisacs to rocks or other surfaces. These ovisacs are adhering to detritus.|
|The appearance of the ovisacs varies among populations. These are from the Spring River in Cherokee County, Kansas.|
|Each ovisac is a bag of several hundred glochidia. The envelop is easily ruptured when a fish bites the ovisac. The eyespots, in particular, are zones of weakness that tend to rupture.|
|Suitable host fish for Ouachita kidneyshells include rainbow and orangethroat darters. In this picture, a potential host examines several ovisacs adhering to a rock. Darters are discriminating feeders, but these baits are hard to resist.|
|In an aquarium, darters attack ovisacs repeatedly, but they seldom if ever actually consume them.|
|Video: This sequence was taken in an aquarium. The file is MPEG-1 and is 1.7 megabytes in size. You will need a suitable player, such as the Windows Media Player that comes with Windows.|
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