Morphology and phylogenetic significance of the pelvic articular region in elasmobranchs (Chondrichthyes).

The morphology of paired fins is commonly overlooked in morphological studies, particularly the pelvic girdle and fins. Consequently, previous phylogenetic studies incorporating morphological data used few skeletal characters from this complex. In this paper, the phylogenetic significance of pelvic articular characters for elasmobranchs is discussed in light of the morphological variation observed in 130 species, the most comprehensive study exploring the morphology of the pelvic girdle done so far. The 10 morphological characters proposed herein for the pelvic articulation were incorporated into a molecular matrix of NADH2 sequences and submitted to an analysis of maximum parsimony employing extended implied weighting. The most stable tree was selected based on the distortion coefficients, SPR distances (subtree pruning and regrafting) and fit values. Some of the striking synapomorphies recovered within elasmobranchs include the presence of an articular surface for the first enlarged pelvic radial supporting Elasmobranchii and the pelvic articular region for the basipterygium extending from the posterolatral margin of the pelvic girdle over its lateral surface in Echinorhinus + Hexanchiformes. Additionally, the proposed characters and their distributions are discussed considering the relationships recovered and also compared with previous morphological and molecular phylogenetic hypotheses.

Morphological study of the oral denticles of the porbeagle shark Lamna nasus.

Oral denticles of sharks are composed by a crown, dentine covered by a layer of enameloid and pulp cavity, the same structure of the dermal denticles found across the body surface of most elasmobranchs. In addition, oral papillae and taste buds are distributed among denticles within the oropharyngeal cavity, playing a fundamental role for tasting as part of the chemosensory system of fishes. Scanning electron microscopy (SEM) has been employed as an important tool for the study of dermal denticles and other structures, as well as histology and more recently computed tomography (CT) scan analysis. Herein, the authors used two methods for the study of the morphology of the oropharyngeal cavity of Lamna nasus (Lamniformes), an oceanic and pelagic shark: SEM and CT scan. The general morphology of oral denticles studied herein is related to abrasion strength as they are diamond-shaped, lack lateral cusps and have less pronounced ridges. In addition, smooth ridges and broad rounded denticles could be related to prevent abrasion during food consumption and manipulation. Oral papillae had a round shape and were observed only under SEM. The densities of papillae were estimated in 100 per cm2 , whereas denticles were 1760 and 1230 cm2 over the dorsal and ventral regions, respectively. The high numbers of denticles are inversely proportional to papillae density; denticles seem to restrict papillae distribution. Regarding the differences between methodologies, under SEM, only the crown was visualized, as well the papillae, allowing the estimation of size and density of both structures. Nonetheless, under CT scan, the whole components of denticles were clearly visualized: different views of the crown, peduncle, basal plate, and pulp cavity. On the contrary, oral papillae were not visualized under CT due to the tissue preparation. Furthermore, both methods are complementary and were important to extract as much information as possible from denticles and papillae.

Phylogenetic interrelationships of the eel families Derichthyidae and Colocongridae (Elopomorpha: Anguilliformes) based on the pectoral skeleton.

A cladistic analysis of the eel families Derichthyidae and Colocongridae is herein proposed for the first time on the basis of morphological data. We discovered dozens of new phylogenetic characters derived from a detailed analysis of the pectoral skeleton, an anatomical system neglected by most previous studies. Our maximum parsimony analysis indicates that Colocongridae sensu lato is paraphyletic, with its two constituent genera Coloconger and Congriscus appearing as successive sister groups of derichthyids. Monophyly of the family Derichthyidae, which has been questioned by some studies, is herein strongly supported by 10 unambiguous synapomorphies. We also stress the importance of the appendicular skeleton as a useful source of phylogenetic information for the resolution of systematic problems within Anguilliformes.

Potamotrygon limai, sp. nov., a new species of freshwater stingray from the upper Madeira River system, Amazon basin (Chondrichthyes: Potamotrygonidae).

Potamotrygon limai, sp. nov., is described from the Jamari River, upper Madeira River system (Amazon basin), state of Rondônia, Brazil. This new species differs from congeners by presenting unique polygonal or concentric patterns formed by small whitish spots better defined over the posterior disc and tail-base regions. Potamotrygon limai, sp. nov., can be further distinguished from congeners in the same basin by other characters in combination, such as two to three rows of midtail spines converging to a single irregular row at level of caudal sting origin, proportions of head, tail and disc, patterns of dermal denticles on rostral, cranial and tail regions, among other features discussed herein. Potamotrygon limai, sp. nov., is most similar to, and occurs sympatrically with, P. scobina, and is distinguished from it by lacking ocellated spots on disc, by its characteristic polygonal pattern on posterior disc, a comparatively much shorter and broader tail, greater intensity of denticles on disc, more midtail spine rows at tail-base, and other features including size at maturity and meristic characters. Potamotrygon limai, sp. nov., is also distinguished from other species of Potamotrygon occurring in the Amazon region, except P. scobina, by presenting three angular cartilages (vs. two or one). This new species was discovered during a detailed taxonomic and morphological revision of the closely related species P. scobina, and highlights the necessity for thorough and all-embracing taxonomic studies, particularly in groups with pronounced endemism and morphological variability.