Morphology and phylogenetic relationships of a remarkable new genus and two new species of Neotropical freshwater stingrays from the Amazon basin (Chondrichthyes: Potamotrygonidae)

Abstract

The morphology and phylogenetic relationships of a new genus and two new species of Neotropical freshwater stingrays, family Potamotrygonidae, are investigated and described in detail. The new genus, Heliotrygon, n. gen., and its two new species, Heliotrygon gomesi, n. sp. (type-species) and Heliotrygon rosai, n. sp., are compared to all genera and species of potamotrygonids, based on revisions in progress. Some of the derived features of Heliotrygon include its unique disc proportions (disc highly circular, convex anteriorly at snout region, its width and length very similar), extreme subdivision of suborbital canal (forming a complex honeycomb-like pattern anterolaterally on disc), stout and triangular pelvic girdle, extremely reduced caudal sting, basibranchial copula with very slender and acute anterior extension, and precerebral and frontoparietal fontanellae of about equal width, tapering very little posteriorly. Both new species can be distinguished by their unique color patterns: Heliotrygon gomesi is uniform gray to light tan or brownish dorsally, without distinct patterns, whereas Heliotrygon rosai is characterized by numerous white to creamy-white vermiculate markings over a light brown, tan or gray background color. Additional proportional characters that may further distinguish both species are also discussed. Morphological descriptions are provided for dermal denticles, ventral lateral-line canals, skeleton, and cranial, hyoid and mandibular muscles of Heliotrygon, which clearly corroborate it as the sister group of Paratrygon. Both genera share numerous derived features of the ventral lateral-line canals, neurocranium, scapulocoracoid, pectoral basals, clasper morphology, and specific patterns of the adductor mandibulae and spiracularis medialis muscles. Potamotrygon and Plesiotrygon are demonstrated to share derived characters of their ventral lateral-line canals, in addition to the presence of angular cartilages. Our morphological phylogeny is further corroborated by a molecular phylogenetic analysis of cytochrome b based on four sequences (637 base pairs in length), representing two distinct haplotypes for Heliotrygon gomesi. Parsimony analysis produced a single most parsimonious tree revealing Heliotrygon and Paratrygon as sister taxa (bootstrap proportion of 70%), which together are the sister group to a clade including Plesiotrygon and species of Potamotrygon. These unusual stingrays highlight that potamotrygonid diversity, both in terms of species composition and undetected morphological and molecular patterns, is still poorly known.

On the origins of marine‐derived freshwater fishes in South America

“…() data set as a backbone, but included only Myliobatiformes and added additional sequences of Potamotrygonidae (South American freshwater stingrays) from Lovejoy et al . (), de Carvalho & Lovejoy (), and Toffoli et al . ().…”

Molecular phylogeny of Potamotrygonocotyle (Monogenea, Monocotylidae) challenges the validity of some of its species

“…Nevertheless, Pa. aiereba and He. gomesi , the respective hosts of P. aramasae and P. tatianae , are sister groups (Carvalho & Lovejoy 2011), a pattern that might be associated with co‐evolution (strict cophylogeny) between these host–parasite lineages.…”

“…2008; Toffoli et al. 2008; Carvalho & Lovejoy 2011), organized in four genera ( Heliotrygon , Paratrygon , Plesiotrygon , Potamotrygon ) and widely distributed across the main Atlantic and Caribbean continental drainages (Thorson 1970; Thorson et al. 1978; Nishida 1990; Carvalho et al.…”

Potamotrygon marquesi, a new species of neotropical freshwater stingray (Potamotrygonidae) from the Brazilian Amazon Basin

“…The subfamily Potamotrygoninae includes neotropical freshwater stingrays that evolved in an exclusively freshwater environment. Four genera are presently recognised as valid within the subfamily (Carvalho et al, ; Carvalho & Lovejoy, ): Potamotrygon Garman 1877, Paratrygon Duméril 1865, Plesiotrygon Rosa et al, and Heliotrygon Carvalho & Lovejoy, . Paratrygon is currently monotypic (although a recent taxonomic revision recognised seven new species within the genus) (Loboda, ), Heliotrygon and Plesiotrygon have two valid species each (Carvalho & Lovejoy, ; Carvalho & Ragno, ; Rosa et al, ) and Potamotrygon is the most diverse genus, including 35 valid species (Carvalho et al, , ; Silva & Carvalho, , ; Loboda & Carvalho, ; Fontenelle et al, ; Silva & Carvalho, , Carvalho, 2016a,b; Fontenelle & Carvalho, ).…”