The Finding of the Second Canestrini’s Organ in Loach Species (Cobitidae) Characterized by a Single Lamina Circularis on the First Branched Ray of the Pectoral Fin in the Mature Males. An Atavism or an Innovation?

We found an additional Canestrini’s organ in some males of Cobitis lutheri, C. derzhavini, and Misgurnus chipisaniensis, which normally have one lamina circularis on the first branched ray of the pectoral fin. We consider this as a manifestation of atavism. In the case of C. lutheri and C. derzhavini, this phenomenon mimics the state observed in the Bibarba lineage, and in the case of the pond loach, in the Bicanestrinia lineage. It is suggested that the primitive ancestral state for the entire Northern Clade of loaches should be considered to be the presence of two or even three laminae circularis in the pectoral fin of sexually mature males. In most lineages this state is lost, however, there probably was a phylogenetic reversion in the ancestor of the Bicanestrinia group through fixation of the atavistic state as a norm.