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.References
Araújo, M.L.G. (1998) Biologia reprodutiva e pesca de Potamotrygon sp. C (Chondrichthyes, Potamotrygonidae) no médio rio Negro, Amazonas. Unpubl. Master’s diss., Instituto Nacional de Pesquisas da Amazônia, Universidade do Amazonas.
Bigelow, H.B. & Schroeder, W.C. (1953) The Fishes of the Western North Atlantic, Part II: Sawfishes, Skates, Rays and Chimaeroids. Memoirs Sears Foundation for Marine Research, (2), 1‒588.
Carvalho, M.R. de, Lovejoy, N.R. & Rosa, R.S. (2003) Family Potamotrygonidae. Pp. 22‒29. In: Reis, R.E, Ferraris Jr, C.J. & Kullander, S.O. (Eds.). Checklist of the Freshwater Fishes of South and Central America. Porto Alegre, EDIPUCRS, 729 pp.
Carvalho, M.R. de, Maisey, J.G. & Grande, L. (2004) Freshwater stingrays of the Green River Formation of Wyoming (Early Eocene), with the description of a new genus and species and an analysis of its phylogenetic relationships (Chondrichthyes: Myliobatiformes). Bulletin of the American Museum of Natural History, 284, 1‒136.
Castex, M.N. (1963) La raya fluvial. Notas histórico-geográficas. Librería y Editorial Castellví, Santa Fe. 120 pp.
Chu, Y.T. & Wen, C.M. (1979) A study of the lateral-line canals system and that of Lorenzini ampullae and tubules of Elasmobranchiate fishes of China. Monograph of Fishes of China. 2. Shangai, People´s Republic of China: Shangai Science and Technology Press.
Compagno, L.J.V. (2005) Checklist of living Chondrichthyes. Pp. 503‒548. In: Hamlett, W. C. (ed.), Reproductive Biology and Phylogeny of Chondrichthyes, Sharks, Batoids and Chimaeras. Science Publishers, Inc. Enfield (NH), USA.
Compagno, L.J.V. & Roberts, T. (1982) Freshwater stingrays (Dasyatidae) of southeast Asia and New Guinea, with description of a new species of Himantura and reports of unidentified species. Environmental Biology of Fishes, 7(4), 321–339.
Deynat, P. & Séret, B. (1996) Le revêntement cutané des raies (Chondrichthyes, Elasmobranchii, Batoidea) I – Morphologie et arrangement des denticules cutanés. Annales des Sciences Naturelles, Zoologie 17 (2), 65‒83.
Deynat, P. (2006) Potamotrygon marinae n. sp., une nouvelle espèce de raies d’eau douce de Guyane (Myliobatiformes, Potamotrygonidae) Comptes Rendu Biologies, 329 (7), 483‒493.
Dingerkus, G. & Uhler, L.D. (1977) Enzyme clearing of alcian blue stained whole smalle vertebrates for demonstration of cartilage. Stain Technology, 52(4), 229‒232.
Ewart, J.C. & Mitchell, H.C. (1892) On the lateral sense organs of elasmobranchs. II. The sensory canals of the common skate (Raja batis). Transactions of the Royal Society of Edinburgh, 37, 87‒105.
Garman, S. (1877) On the pelvis and external sexual organs of selachiens, with special reference to the new genera Potamotrygon and Disceus. Proceedings of the Boston Society of Natural History, 19, 197–215.
Garman, S. (1888) On the lateral canal system of the Selachia and Holocephala. Bulletin of the Museum of Comparative Zoology, 17, 57‒119.
Garman, S. (1913) The Plagiostomia (sharks, skates and rays). Memoirs of the Museum of Comparative Zoology 36, 515p., 77 plates.
Hubbs, C.L. & Ishiyama, R. (1968) Methods for the taxonomic study and description of skates (Rajidae). Copeia, 1968 (3), 483‒491.
Ishihara, H. & Taniuchi, T. (1990) A strange potamotrygonid ray (Chondrichthyes: Potamotrygonidae) from the Orinoco river system. Pp. 91–97. In: Oetinger, M. I. & Zorzi, G. D (Eds.), The Biology of Freshwater Elasmobranchs, a symposium to honor Thomas B. Thorson. Journal of Aquariculture and Aquatic Sciences, 7, 162 p.
Last, P.R. & Compagno, L.J.V. (1999) Dasyatididae. Stingrays. Pp. 1479–1505. In: Carpenter, K.E. & Niem, V.H. (Eds.) FAO species identification guide for fishery purposes. The living marine resources of the Western Central Pacific. Vol. 3. Batoid fishes, chimaeras and bony fishes part 1 (Elopidae to Linophrynidae). FAO, Rome.
Last, P.R. & Stevens, J.D. (2009) Sharks and rays of Australia. 2nd Edition. Cambridge, Mass.: Harvard University Press; 644 p.
Lovejoy, N.R. (1996) Systematics of myliobatoid elasmobranchs: with emphasis on the phylogeny and historical biogeography of neotropical freshwater stingrays (Potamotrygonidae: Rajiformes). Zoological Journal of the Linnaean Society, 117, 207‒257.
Lovejoy, N.R., Birminghan, E. & Martin, A.P. (1998) South American rays came in with the sea. Nature, 396, 42‒422.
McEachran, J.D., Dunn, K.A. & Miyake, T. (1996) Interrelationships within the batoid fishes (Chondrichthyes, Batoidea). Pp. 63‒84. In: Stiassny, M.L.J.; Parenti, L.R. & Johnson, G.D. (eds.). Interrelationships of Fishes. Academic Press, New York.
Miyake, T., McEachran, J.D & Hall, B.K. (1988) Edgeworth’s legacy of cranial muscle development with an analysis of muscles in the ventral gill arch region of batoid fishes (Chondrichthyes: Batoidea). Journal of Morphology, 212, 213‒256.
Müller, J. & Henle, F.G.J. (1841) Systematische beschreibung der Plagiostomen. Verlag von Veit, Berlin.
Nishida, K. (1990) Phylogeny of the suborder Myliobatidoidei. Memoirs of the Faculty of Fisheries Hokkaido University 37 (1/2), 1‒108.
Rosa, R.S. (1985a) A systematic revision of the South American freshwater stingrays (Chondricthyes: Potamotrygonidae). Unpublished PhD diss., College of William and Mary, Williamsburg, xvi + 523p.
Rosa, R.S. (1985b). Further comment on the nomenclature of the freshwater stingray Elipesurus spinicauda Schomburgk, 1843 (Chondrychthyes, Potamotrygonidae). Revista Brasileira de Zoologia, 3(1), 27‒31.
Rosa, R.S. (1990) Paratrygon aiereba (Muller & Henle, 1841): the senior synonym of the freshwater stingray Disceus thayeri Garman, 1913 (Chondrychthyes: Potamotrygonidae). Revista Brasileira de Zoologia 7(4), 425‒437.
Rosa, R.S., Castello, H.P. & Thorson, T.B. (1987) Plesiotrygon iwamae, a New Genus and Species of Neotropical Freshwater Stingray (Chondrychthyes: Potamotrygonidae). Copeia, 1987 (2), 447‒458.
Rosa, R.S., Carvalho, M. R. de & Wanderley, C.A. (2008) Potamotrygon boesemani (Chondrichthyes: Myliobatiformes: Potamotrygonidae), a new species of Neotropical freshwater stingray from Surinam. Neotropical Ichthyology, 6 (1), 1‒8.
Rosa, R.S., Charvet-Almeida, P. & Quijada, C.C.D. (2010) Biology of the South American potamotrygonid stingrays. Pp. 241–281. In: Carrier, J.C.; Musick, J.A. & Heithaus, M.R. (Eds.), Sharks and Their Relativies Ii: Biodiversity, Adaptative Physiology, and Conservation. CRC Press, Florida.
Ross, R.A. & Schäfer, F. (2000) Aqualog Süsswasser Rochen: Freshwater Rays. Verlag ACS, Mörfelden-Walldorf.
Silva, J.P.C.B. da & Carvalho, M.R. de (in press) A taxonomic and morphological redescription of Potamotrygon falkneri Castex & Maciel, 1963 (Chondrichthyes: Myliobatiformes: Potamotrygonidae). Neotropical Ichthyology, 2011.
Swofford, D.L. (2002) PAUP*. Phylogenetic Analysis Using Parsimony (*and Other Methods). Version 4.0b10. Sinauer Associates, Sunderland, MA.
Taniuchi, T. & Ishihara, H. (1990) Anatomical comparison of claspers of freswater stingrays (Dasyatidae and Potamotrygonidae). Japanese Journal of Ichthyology, 37 (1), 10‒16.
Thorson, T.B., Brooks, D.R. & Mayes, M.A. (1983) The evolution of freshwater adaptation in stingrays. National Geographic Society Research Reports, 15, 663–694.