Psilorhynchus balitora

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 : 80-81

B. Psilorhynchus balitora bone with an expanded spoon-like ventral portion. It bears a short canal through its middle portion that connects the otic sensory canal with the lateral line canal. The dorsal edge of the supracleithrum articulates directly with the neurocranium, and there is no separate post-temporal in any of the specimens examined, suggesting that this element is either absent or fused with the element identified as the supracleithrum early in ontogeny. There is no postcleithrum.

The relatively large mesocoracoid is situated medial to the cleithrum. Only its posteriormost edge is visible in lateral view. It is L-shaped in general appearance, exhibiting two arms, a dorsal arm and a more ventral arm that contacts the medial face of the cleithrum, enclosing a large foramen in between. The ventral portion of the mesocoracoid is closely associated with the coracoid. The coracoid contacts the cleithrum ventromedially to form a large oblong foramen that extends posteriorly, beneath the lower arm of the mesocoracoid, opening on the lateral face of the girdle, dorsal to the scapula. The scapula is wedged between the posteroventral point of the cleithrum and the lateral edge of the coracoid. A thin slip of cartilage, a remnant of the scapulocoracoid cartilage, separates the scapula from the coracoid. A small foramen, for the passage of a branch of the pterygial nerve, is situated in the scapula close to its point of contact with the cleithrum.

There are four pectoral radials and a variable number of distal radials and distal radial cartilages ( Fig. 19A ). Pectoral radial one is a small irregularly shaped bone that is tightly bound to the posterior edge of the scapula. The remaining pectoral radials are roughly rod-shaped bones that articulate with the posterior edge of the coracoid. In the largest specimen examined (39.9-mm SL) there are six endochondrally ossified distal radials, situated between the posterior tips of the pectoral radials and the articulating heads of the fin rays. A single distal radial cartilage is situated at the posterior tip of pectoral radial 2. In specimens smaller than 16.4-mm SL, only the posteriormost distal radial cartilage is ossified endochondrally.

There are iv.7.i or iv.7.ii pectoral fin rays. The anteriormost unbranched pectoral fin ray articulates with the lateral edge of the scapula. Its head is greatly enlarged in the typical teleost fashion, resulting from the ontogenetic fusion of the propterygium ( Patterson, 1977). The heads of the preceding rays are also modified: the heads of their ventral hemitrich are roughly triangular in shape, with their tips oriented posteromedially. The head of the second unbranched ray, though not as massive as that of the first, is also much larger than the head of succeeding rays, which become progressively smaller towards the posterior. 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. Peculiar, small finger-like projections are present along the entire leading edge of the first unbranched ray and the tips of the second and third unbranched ray. These small finger-like projections are borne only on the anterior edge of segments of the dorsal hemitrich.

Comparisons

The pectoral girdle of the other species of Psilorhynchus examined are similar in general appearance to the pectoral girdle of P. sucatio , differing only in the shape of certain bones and the number of distal radials and distal radial cartilages ( Figs 18B–F, 19B– F ). In P. balitora , P. breviminor , P. gracilis , P. rahmani , P. tenura , and P. brachyrhynchus , only distal radial cartilages are present ( Fig. 19B–D ). In P. robustus , P. pseudecheneis , P. pavimentatus , and P. melissa , both distal radials and distal radial cartilages are present ( Fig. 19E, F ). As in P. sucatio , the two anteriormost distal radial elements (bone or cartilage) associated with the posterior edge of pectoral radial 1 are larger than succeeding distal radial elements in all other species examined. In P. robustus the anteriormost distal radial is a large, irregularly shaped element ( Fig. 19E ) that articulates with the base of the four anteriormost unbranched rays, and may represent the ontogenetic fusion of several smaller distal radial elements. In P. gracilis , P. robustus , and P. melissa , the dorsal edge of pectoral radial 3 bears a short dorsomedially directed process ( Fig. 18D, E), close to the point of articulation with the coracoid that is absent in the other species examined. Like P. sucatio , all other species of Psilorhynchus examined lack the post-temporal, and the pectoral girdle articulates with the neurocranium via the supracleithrum. Peculiar, small finger-like projections are also present along the entire leading edge of the first unbranched ray and the tips of the second and third unbranched rays in all other species of Psilorhynchus examined ( Fig. 20 ). As in P. sucatio , these projections are borne only along the anterior edge of segments of the dorsal hemitrich.

PELVIC GIRDLE

Psilorhynchus sucatio

The pelvic girdle of P. sucatio is illustrated in Figure 21A , and pelvic fin ray counts are provided in Table 1. The pelvic girdle consists of a pair of flat and elongate basipterygia, each supporting two unbranched and six or seven branched fin rays (ii.6.i or ii.7). Anteriorly, the basipterygium bears two spine-like processes (termed external and internal

Figures

Figure 19. Pectoral radials of Psilorhynchus, left side in lateral view. Anterior to top of page. 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 205345, paratype, 39.1-mm SL. D, Psilorhynchus robustus, CMK 17941, paratype, 58.1-mm SL. D, Psilorhynchus pseudecheneis, KU 29519, 40.3-mm SL. Cartilage highlighted in grey. Abbreviations: DR, distal radial; DRC, distal radial cartilage; PeR1–4, pectoral radial 1–4.

Figure 20. Portion of the anteriomost pectoral fin ray of Psilorhynchus, left side in dorsal view, illustrating fingerlike projections borne along the anterior edge of segments of the upper hemitrich. Anterior to top of page. A, Psilorhynchus balitora, UMMZ 244782, 31.2-mm standard length (SL). B, Psilorhynchus breviminor, ZRC 43452, paratype, 32.0-mm SL. C, Psilorhynchus pseudecheneis, KU 29519, 40.3-mm SL. Abbreviation: S, segment.

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.