Dermal denticle diversity in sharks: novel patterns on the interbranchial skin

Shark skin is covered in dermal denticles – tooth-like structures consisting of enameloid, dentine, and a central pulp cavity. Previous studies have demonstrated differences in denticle morphology both among species and across different body regions within a species, including one report of extreme morphological variation within a 1 cm distance on the skin covering the branchial pouches, a region termed “interbranchial skin”. We used gel-based profilometry, histology, and scanning electron microscopy to quantify differences in denticle morphology and surface topography of interbranchial skin denticles among 13 species of sharks to better understand the surface structure of this region. We show that 1) interbranchial skin denticles differ across shark species, and 2) denticles on the leading edge of the skin covering each gill pouch have different morphology and surface topography compared to denticles on the trailing edge. Across all species studied, there were significant differences in denticle length (P = 0.01) and width (P = 0.002), with shorter and wider leading edge denticles compared to trailing edge denticles. Surface skew was also higher in leading edge denticles (P = 0.009), though most values were still negative, indicating more valleys than peaks. Overall, leading edge denticles were smoother-edged than trailing edge denticles in all of the species studied. These data suggest two hypotheses: 1) smoother-edged leading edge denticles protect the previous gill flap from abrasion during respiration, and 2) ridged denticle morphology at the trailing edge might alter water turbulence exiting branchial pouches after passing over the gills. Future studies will focus on determining the relationship between denticle morphology and water flow by visualizing fluid motion over interbranchial denticles during in vivo respiration.

Novel method for the extraction of DNA from Lamniformes tooth and denticle enamel Suitable for PCR

Extraction of high-quality genomic DNA from Lamniformes tooth fragment and dermal denticle enamel is discussed as a method of identifying individual sharks. We describe a procedure that permits isolation of genomic DNA of satisfactory size and quality for PCR analysis, as well as for most routine cloning applications. This method should allow for the non-invasive collection of genomic samples from Lamniformes.

Two new species of freshwater stingrays of the genus Paratrygon (Chondrichthyes: Potamotrygonidae) from the Orinoco basin, with comments on the taxonomy of Paratrygon aiereba

The genus Paratrygon, currently recognized as the sole monotypic genus of the family Potamotrygonidae, has a considerably greater diversity than previously indicated, including molecular studies, which supported P. aiereba (hitherto the only recognized species in the genus) as a possible species complex. Here we describe two new species of the genus that are both endemic to and sympatric in the Orinoco basin. Paratrygon aiereba, type species of the genus, is now restricted to the Amazon basin. Both new species are identified and defined through morphological characters such as coloration, dermal denticle morphology, arrangement of thorns, distribution and morphology of ventral lateral line canals, morphology of skeletal elements, and morphometrics. An extensive comparison of these characters between the new species herein described and P. aiereba is presented. Finally, a taxonomic reappraisal of P. aiereba is provided through a revision of preserved material and its original description, plus new evidence about its type-locatity, collectors, and a reconsideration of the destination of its type-specimen.

Investigation on the genus Squalus in the Sardinian waters (Central-Western Mediterranean) with implications on its management

In the Mediterranean Sea, in addition to the two historically known species belonging to the Squalus genus, a third species, Squalus megalops, has been reported. Considering the high level of morphologic similarity of this species with the native species S. blainville, this study aims to evaluate the Central-Western Mediterranean spurdog population in order to test the hypothesis of the presence of two distinct species S. blainville and S. megalops. A total of 137 spurdogs, caught in the Sardinian waters, were analyzed morphologically and genetically after their subdivision into two groups depending on the number of the lateral processes in the chondrocranium basal plate. The CAP analysis, employing all body and chondrocranial measurements, revealed no clear segregation among the a priori assigned groups with a high misclassification percentage. Besides, no evident dissimilarities in teeth and dermal denticle morphology between the two groups were observed. All the 18 specimens which were genetically analyzed, by sequencing of the mtDNA marker COI, clustered together resulting to be S. blainville. All the obtained results indicated the presence, in the study area, of only one species, ascribable to S. blainville.