Specific features of the seismosensory system and their use in the systematics of five families of the order pleuronectiformes

Abstract

The structure of the seismosensory system (SSS) was studied in 23 species of 13 genera from the families Rhombosoleidae, Poecilopsettidae, and Samaridae, and a comparison and generalization of the obtained data with those published previously for the families Psettodidae and Pleuronectidae was performed. It was shown that the individual variability of SSS does not concern topography of canals, being manifested in the variation of the number of pores in particular canals. Interspecific differences also concern mainly the number of pores, and revealing these differences requires, as a rule, statistic methods. Considerable differences were found between genera, so that each of the 40 studied genera can be characterized by a unique combination of SSS characters whose polarization was established on the basis of a reduction trend of SSS transformations common for bony fish. The maximum number of plesiomorphies of SSS was found in the genus Psettodes (Psettodidae). In the framework of the family Pleuronectidae, the most generalized structure of SSS was found in representatives of the subfamily Hippoglossinae, and the most advanced, in Pleuronectinae. In the family Rhombosoleidae, the most generalized structure of SSS is in the genus Oncopterus, the remaining representatives of the family Rhombosoleidae are characterized by a different degree of its reduction. In rather closely related families Poecilopsettidae and Samaridae, SSS is considerably reduced, which may be connected with the miniatuarization of their representatives. A small number of considered characters and a high level of homoplasia hinders their use in cladistic study; however, considerable differences between the studied genera and a low interspecific variation permits for the considering of specific features of SSS as valuable diagnostic characters of genera, and the degree of reduction of this system can indicate the relative degree of advancement of a specific taxon of Pleuronectiformes.