Interdigitation Pattern of Dorsal-fin Pterygiophores and Neural Spines, an Important Diagnostic Character for Symphurine Tonguefishes (Symphurus: Cynoglossidae: Pleuronectiformes)

Numbers of proximal dorsal-fin pterygiophores in each of the anterior most five interneural spaces (ID patterns) were examined in 69 of 71 nominal species of symphurine (Symphurus) tonguefishes and were found to be of diagnostic value. All species of Symphurus typically have a single pterygiophore inserted into the first interneural space, a unique arrangement among the Cynoglossidae and related taxa that supports the monophyly of the genus. All but seven species in the genus usually have two pterygiophores inserted into interneural spaces four and five. Observed variation among species in ID patterns, therefore, results primarily from different numbers of pterygiophores inserting into interneural spaces two and three. Formulae for individual ID patterns listed below, with a single exception, are abbreviated to represent the pterygiophore arrangements in the first three interneural spaces. Nine different predominant ID patterns were discovered among 69 species examined. These patterns and the numbers of nominal species (in parentheses) possessing each are as follows: 1-2-2-1-2 (7); 1-2-2 (16); 1-2-3 (3); 1-3-2 (15); 1-3-3 (4); 1-3-4 (1); 1-4-2 (4); 1-4-3 (11); and 1-5-3 (8). Overall, average fidelity for the predominant ID pattern was approximately 78% per species, with values ranging from 37 to 100% per species. Forty-eight species had 70% or more of the individuals possessing the predominant ID pattern; seven had 60% or more with the predominant ID pattern; and only four of 69 species had 50% or fewer of the individuals with the predominant ID pattern. Less than 5% of the individuals per species had anomalous ID patterns that provided little or no useful information for identification of the specimens. Between 0 and 37% of the individuals for most species had variant ID patterns that were predominant patterns recorded for other species. Twenty of 24 New World species with 1-3-4, 1-4-2, 1-4-3, and 1-5-3 ID patterns had between 0 and 43% of the individuals per species with secondary ID patterns that occurred uniquely in species characterized by these predominant ID patterns. Intraspecific variation in ID patterns was limited and predictable for each species and was found to be largely non-overlapping among species with different predominant patterns. ID patterns are an important diagnostic character for Symphurus, especially when used in combination with caudal- and dorsal-fin ray counts. Geographical ranges of species characterized by each predominant ID pattern were plotted within four major marine faunal regions revealing interesting distributions for species with different predominant patterns. Species with 1-2-2-1-2 and 1-2-2 ID patterns occur predominantly, while those with a 1-2-3 occur exclusively, in deep-sea habitats throughout temperate and tropical regions of the Indo-Pacific. Only one species with a 1-2-2-1-2 ID pattern and two with the 1-2-2 pattern occur in the Atlantic, while no species with these three ID patterns is found in the eastern Pacific. Species characterized by other ID patterns are not found in the Indo-Pacific region. Those with the 1-3-2 and 1-3-3 ID pattern occur only in northern and southern hemispheres of the Atlantic Ocean and in the tropical eastern Pacific from the Gulf of California to northern Peru. Species with 1-3-4, 1-4-2, 1-4-3, and 1-5-3 ID patterns are found only in the New World. Symphurus calfopterus, the only species with the 1-3-4 ID pattern, and all species with the 1-5-3 ID pattern occur in temperate and tropical regions of the eastern Pacific. Four species characterized by the 1-4-2 ID pattern occur entirely in the western Atlantic, while those with a 1-4-3 pattern occur in shallow-water environments of the western Atlantic and eastern Pacific Oceans.