Structure of lateral-line scales in representatives of families of the order pleuronectiformes.

Structure of nonmodified scales and lateral-line scales ( Sll) is compared in 179 species of 105 genera of 13 families of the order Pleuronectiformes. Morphological diversity of Sll depends on the level of development and of interaction of two component parts—the scale plate and the tubular part. Of the considered characters, the most individually variable character is whether the tubular part is complete or incomplete. The interspecies differences may manifest themselves in structure of the scale plate, the level of unification of opening of the tubular part and of the cutaneous canaliculus, or in completeness or incompleteness of the tubular part. As a rule, Sll in species of the same genus is similar in structure. In some cases, special traits of this structure may be diagnostic characters of genera and contribute to the solution of controversial issues of generic position of species. The families of Pleuronectiformes are characterized by a different ratio of taxa with certain involved characters of nonmodified scales and Sll. However, their distribution in this order does not give a simple idea on their relationships and on the direction of evolutionary transformations. This follows from the fact that the structure of Sll depends on a wide complex of factors—morphogenesis of nonmodified scales, level of ossification of trunk canal, time of anlage, and mutual influence of these structures at early stages of ontogenesis. [ABSTRACT FROM AUTHOR]