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. 

Click on the thumbnails for larger images.

kidney-0.jpg (59476 bytes) 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. 
kidney-1.jpg (26116 bytes) 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. 
packets-1.jpg (42838 bytes) 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.
packets-2.jpg (29949 bytes) The appearance of the ovisacs varies among populations. These are from the Spring River in Cherokee County, Kansas.
packets-3.jpg (28219 bytes) 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.
po-lure2.jpg (57215 bytes) 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.
po-lure3.jpg (38858 bytes)  In an aquarium, darters attack ovisacs repeatedly, but they seldom if ever actually consume them.  
vidclip.jpg (31770 bytes) 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. 


Unio Gallery Home Page http://unionid.missouristate.edu.  Copyright 1998-2006 by M. C. Barnhart.  Please see Usage Policy for conditions of use of images and video.