Molecular evidence supporting the expansion of the geographical distribution of the Brazilian cownose ray Rhinoptera brasiliensis (Myliobatiformes: Rhinopteridae) in the western Atlantic.

The genus Rhinoptera is composed of eight species widely distributed in tropical, subtropical and temperate coastal waters, which inhabit bays, estuaries and river mouths. Cownose ray Rhinoptera bonasus has been reported to inhabit the Western Atlantic including the Gulf of Mexico and the Caribbean, whereas the Brazilian cownose ray R. brasiliensis has been considered endemic to the coast of Brazil. Recent reports of R. brasiliensis in the Gulf of Mexico bring about the question of whether the species has a wider range than previously reported. Here, the mitochondrial genes COI, Cytb, NADH2 and the nuclear gene RAG1 were used to distinguish among species and to confirm the presence of R. brasiliensis in the Gulf of Mexico. R. brasiliensis specimens collected along the southern Gulf of Mexico showed a remarkable genetic and morphological affinity when compared with R. brasiliensis specimens from Brazil, supporting the presence of the species in Mexico (from Veracruz through Campeche) and providing evidence that its distribution ranges from Brazil to the Caribbean Sea and the Gulf of Mexico. Both species overlap geographically to a large degree, leading to a reassessment of their conservation status. Our results also show that R. bonasus distribution in the Gulf of Mexico may be restricted to the northern portion, in US waters.

A preliminary investigation into the morphology of oral papillae and denticles of blue sharks (Prionace glauca) with inferences about its functional significance across life stages.

Sensory organs in elasmobranchs (sharks, skates, rays) detect and respond to a different set of biotic and/or abiotic stimuli, through sight, smell, taste, hearing, mechanoreception and electroreception. Although gustation is crucial for survival and essential for growth, mobility, and maintenance of neural activity and the proper functioning of the immune system, comparatively little is known about this sensory system in elasmobranchs. Here we present a preliminary investigation into the structural and dimensional characteristics of the oral papillae and denticles found in the oropharyngeal cavity of the blue shark (Prionace glauca) during embryonic development through adulthood. Samples were obtained from the dorsal and ventral surface of the oropharyngeal cavity collected from embryos at different development stages as well as from adults. Our results suggest that development of papillae occurs early in ontogeny, before the formation of the oral denticles. The diameter of oral papillae gradually increases during development, starting from 25 µm in stage I embryos, to 110 µm in stage IV embryos and 272-300 µm in adults. Embryos exhibit papillae at early developmental stages, suggesting that these structures may be important during early in life. The highest density of papillae was observed in the maxillary and mandibular valve regions, possibly related to the ability to identify, capture and process prey. The oral denticles were observed only in the final embryonic stage as well as in adults. Accordingly, we suggest that oral denticles likely aid in ram ventilation (through reducing the hydrodynamic drag), to protect papillae from injury during prey consumption and assist in the retention and consumption of prey (through adhesion), since these processes are only necessary after birth.