Psilorhynchus sucatio

Conway, Kevin W., 2011, Osteology of the South Asian Genus Psilorhynchus McClelland, 1839 (Teleostei: Ostariophysi: Psilorhynchidae), with investigation of its phylogenetic relationships within the order Cypriniformes, Zoological Journal of the Linnean Society 163 (5), pp. 50-154 : 82-83

A. Psilorhynchus sucatio B. Psilorhynchus balitora

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processes by Sawada, 1982). The more lateral of these two processes reaches further anteriorly than the medial process, which is wider than the former. From the anteriormost point, the basipterygium gradually increases in width towards the posterior, until reaching its widest point, slightly anterior to the first unbranched fin ray. Posterior to the first unbranched fin ray, the basipterygium decreases in width, ultimately terminating in a plate-like ischiac process on its posteriomedial edge. A small foramen is present on the lateral edge of the basipterygium, anterior to the point of articulation of the first unbranched ray. There are three endochondrally ossified pelvic radials. The lateralmost radial, pelvic radial 1, is roughly rectangular in shape and larger than pelvic radial 2, which is a small circular bone. The medialmost radial, pelvic radial 3, is roughly triangular in shape, extending farthest posteriorly at its point closest to the midline. Situated anterodorsal to the first unbranched fin ray is a small spindle-like bone, termed the pelvic splint by Gosline (1961), that is oriented with its anteriormost tip directly below the tip of the 11 th or 12 th pleural rib, to which it is firmly attached through a ligamentous connection. The heads of the fin rays tightly articulate with the posterior edge of the basipterygium and the pelvic radials. The heads of the ventral hemitrich of each ray are roughly triangular in shape, with their tips oriented posteromedially. The head of the anteriormost unbranched ray is much larger than that of more medial rays, which become progressively smaller medially. The individual segments of the hemitrichia of the unbranched rays are greatly foreshortened (sensu Lundberg & Marsh, 1976), compared with the individual segments of the hemitrichia of the branched rays. The entire anterior edge of the segmented part of the first unbranched ray, and the tip of the second, exhibits similar fingerlike projections to those present along the anterior edge of the unbranched pectoral fin rays. As is the case for the unbranched pectoral rays, these small finger-like projections are borne only on the anterior edge of segments of the dorsal hemitrich.

Comparisons

The pelvic girdle of the majority of the other species of Psilorhynchus examined is very similar in general form to that of P. sucatio , differing only in terms of shape and by the absence of a lateral basipterygial foramen ( Fig. 21B–E ). The pelvic girdle of P. pseudecheneis ( Fig. 21F ) differs markedly from that of P. sucatio and the other species of Psilorhynchus examined. In this latter species the basipterygium is a broad, shield-shaped structure that lacks anterior processes. The lateral foramen of the basipterygium of P. pseudecheneis is also much larger than that of P. sucatio , and is associated with the ventralmost tip of the enlarged pleural rib of the 13 th or 14 th vertebral centra.

SCALES

Psilorhynchus sucatio

The cycloid scales are relatively large, flexible, and regionally variable in terms of size and shape. Scales dorsal and ventral to the scale row bearing the lateral line canal possess between three and six posteriorly directed radii that arise around the scale focus ( Fig. 22A ). Three shorter anteriorly directed radii also arise at this point. Scales bearing the lateral line canal are similar in shape to other flank scales. They bear the thin canal on their posterior portion only, with the canal pore positioned close to the posterior edge of the scale.

Comparisons

The scales of the other species of Psilorhynchus examined are similar in general appearance to those of P. sucatio , but differ most obviously by the complete lack of anteriorly directed radii and by a higher number of posteriorly directed radii ( Fig. 22B–F ). In P. balitora , P. breviminor , P. gracilis , P. melissa , P. nepalensis , P. pavimentatus , P. rahmani , P. robustus , P. tenura , and P. brachyrhynchus , there are between six and eight posteriorly directed radii on scales dorsal and ventral to the lateral line canal scale row. The scales of P. pseudecheneis are smaller than those of the other species of the genus (as noted by Yazdani, Singh & Rao, 1991), and possess between ten and 13 posteriorly directed radial furrows ( Fig. 22F ).

Figures

Figure 21. Pelvic fin skeleton of Psilorhynchus, in ventral view. Anterior to left. A, Psilorhynchus sucatio, CAS 50289, 39.9-mm standard length (SL). B, Psilorhynchus balitora, UMMZ 244782, 31.2-mm SL. C, Psilorhynchus breviminor, ZRC 43452, paratype, 32.0-mm SL. D, Psilorhynchus gracilis, KU 29143, 33.5-mm SL. E, Psilorhynchus robustus, CMK 17941, paratype, 58.1-mm SL. F, Psilorhynchus pseudecheneis, KU 29519, 40.3-mm SL. Right-side fin rays removed to reveal radials. First pelvic fin ray malformed in E. Cartilage highlighted in grey. Abbreviations: Bp, basipterygium; BpF, basipterygium foramen; PS, pelvic splint; PR, pelvic radial; PRC, pelvic radial cartilage; R, pelvic fin ray.

Figure 22. Scale from row dorsal to lateral line scale row, removed from mid-body region, below dorsal fin origin of left side (image reversed). Anterior to left. A, Psilorhynchus sucatio, CAS 50289, 39.9-mm standard length (SL). B, Psilorhynchus balitora, UMMZ 244782, 31.2-mm SL. C, Psilorhynchus breviminor, ZRC 43452, paratype, 32.0-mm SL. D, Psilorhynchus gracilis, UMMZ 205343, 49.9-mm SL. E, Psilorhynchus robustus, CMK 17941, paratype, 58.1-mm SL. F, Psilorhynchus pseudecheneis, KU 29519, 40.3-mm SL.