Left-right Reversal Arrangement of Glochidial Threads in Sinanodonta lauta (Bivalvia: Unionidae)

Abstract

This is the first report on the left-right reversal arrangement of organs in Sinanodonta lauta glochidia. A glochidial larva possesses a pair of subtriangular-shaped shells, a pair of claw-like hooks with spines at the ventral margin, internal and external glochidial threads, four pairs of sensory hair tufts and one adductor muscle. The arrangement of the internal thread and the origin of the external thread is asymmetric between the pair of valves. As a result of examination of approximately 50 glochidia by light microscopy, one was observed with the internal thread and the origin of the external thread positioned on the left valve. These morphological features are positioned on the right valve in normal glochidia. The relative position of these threads between abnormal and normal glochidia represents a left-right reversal.