Psilorhynchus, McClelland, 1839

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 : 134-135

OF PSILORHYNCHUS

Several authors have commented on or have provided information on the osteology of Psilorhynchus , including Hora (1920, 1925), Mukerji (1933), Hora & Mukerji (1935), Ramaswami (1952), Chen (1981), Yazdani et al. (1991), Yazdani & Singh (1991), Nebeshwar et al. (2007), Conway & Mayden (2007), and Conway & Kottelat (2010). The majority of these accounts are restricted osteologically (focusing mainly on the bony swim-bladder capsule, the pelvic girdle, the caudal skeleton, or aspects of the gill arches), and all are restricted taxonomically, focusing on relatively few species of Psilorhynchus . The most complete account of the osteology of Psilorhynchus provided prior to the present description is that of Ramaswami (1952). In his account of the osteology of Psilorhynchus, Ramaswami (1952) provided a brief description of the neurocranium, hyopalatine arch, opercular series, infraorbital series, gill arches, Weberian apparatus, and caudal skeleton of P. sucatio , based on a single alizarin specimen, cleared in KOH. Ramaswami (1952) made no mention of the remainder of the axial skeleton or the paired fin girdles, other than a cursory remark concerning the point of articulation between the pectoral girdle and the neurocranium. Despite these shortcomings, the results of the present study are in good agreement with those of Ramaswami (1952), with a few notable exceptions. Ramaswami (1952: 145) described and illustrated a connection between the supraorbital sensory canals across the dorsal midline, posterior to the preepiphysial fontanelle at the level of the epiphysial bar. No such connection exists between the supraorbital sensory canals in the specimens of P. sucatio available to me for examination. It is possible that Ramaswami may have misinterpreted the outline of the epiphysial bar in his alizarin-stained specimen as a connection between the supraorbital sensory canals. Ramaswami (1952: 145) also identified the dorsalmost element of the pectoral girdle that articulates with the neurocranium in P. sucatio as the posttemporal, an element identified as the supracleithrum in the present study, and reported the presence of six hypural elements in the caudal skeleton ( Ramaswami, 1952: 147). The lower hypural count provided herein for P. sucatio and other species of the genus ( Table 1) is explained by the identification of the parhypural as hypural 1 by Ramaswami (1952).

Based on his investigation of P. sucatio, Ramaswami (1952) listed numerous features of Psilorhynchus that he considered to differ markedly from the general condition exhibited by members of the Cyprinidae , including: (1) the rostral process of the maxilla not forked; (2) an elongate palatine that articulates laterally with infraorbital 1; (3) the presence of a ‘unique’ ethmoid–frontal fontanelle (= preepiphysial fontanelle); (4) the absence of a lateral process on the lateral ethmoid; (5) the frontals expanded laterally and the absence of the supraorbital; (6) the enlargement of the lacrimal (= infraorbital 1); (7) the hyomandibular articulating with the sphenotic (= autosphenotic) via a singular articular head; and (8) an elongate basihyal, a single pair of hypobranchials, and a single row of teeth on ceratobranchial 5. Based on these characters, Ramaswami (1952: 148) considered Psilorhynchus ‘sufficiently distinctive’ from members of the Cyprinidae to warrant Hora’s (1925) earlier placement of Psilorhynchus within its own family, the Psilorhynchidae . Examination of additional species of Psilorhynchus reveals that many of these ‘distinctive’ features listed by Ramaswami (1952) are also present in other species of Psilorhynchus , and in fact represent synapomorphies in support of the monophyly of Psilorhynchus (see below). However, P. sucatio is unique amongst species of Psilorhynchus in possessing an elongate, rod-like basihyal, and in its retention of hypobranchial-3 cartilage (other species of Psilorhynchus possess hypobranchial 3). These features must be reinterpreted as autopomorphies of P. sucatio , and not derived characteristics of the genus, such as the characters described below (see section on ‘Monophyly of Psilorhynchus ’).

PHYLOGENETIC POSITION OF PSILORHYNCHUS