Crossocheilus reticulatus

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 : 122-125

A. Crossocheilus reticulatus

1 mm

free; (1) proximal segments of each hemitrich fused, forming a ‘spine’-like ray (CI = 1.00; RI = 1.00).

In barbine cyprinids the proximal segments of each hemitrich of the third unbranched ray are fused proximally and form a ‘spine’-like base to the ray. A similar, albeit non-homologous, condition is exhibited ·

by members of the order Siluriformes ( Reed, 1924) . In other cypriniform fishes and in outgroup taxa the proximal segments of each hemitrich of the third unbranched ray remain separate.

119. Terminal compound centrum ( Fink & Fink, 1981: character 110): (0) preural centrum 1, ural centrum 1, and ural centrum 2 separate; (1) preural centrum 1, ural centrum 1, and ural centrum 2 fused, forming a compound centrum (CI = 1.00; RI = 1.00).

In cypriniform fishes, and other ostariophysans, the terminal vertebral element is hypothesized to represent a compound element, resulting from the fusion of preural centrum 1, ural centrum 1, and ural centrum 2 ( Fink & Fink, 1981). In the non-ostariophysan outgroups included for analysis, excluding members of the Clupeiformes , the terminal elements of the vertebral column remain separate ( Schultze & Arratia, 1988, 1989; Hilton, 2002; Hilton & Britz, 2010; but see Schultze & Arratia, 1988, 1989 for a different interpretation of the ural elements of Hiodon ). A compound centrum is also present in certain clupeiforms, and this has been interpreted as evidence for a close relationship between the Clupeiformes and the Ostariophysi ( Lecointre & Nelson, 1996) . In Denticeps clupeoides preural centrum 1 is separate from the next posterior ural element (which is interpreted to represent a compound element resulting from the fusion of ural centra 1 and 2, based on relationships between hypural and ural elements; following Greenwood, 1968). Although there is probably a certain degree of fusion between the ural centra in D. clupeoides (and other clupeiforms) during their ontogeny, this taxon was coded as exhibiting the plesiomorphic condition simply because preural centrum 1 remains separate from the ural centra, and thus differs from the condition present in ostariophysans. An ontogentic perspective on the terminal compound element of ostariophysan and clupeiform fishes is urgently needed to provide a fresh perspective on the terminal vertebral elements of these fishes, and is forthcoming (G. Arratia, pers. comm.).

120. Number of epurals ( Fink & Fink, 1981: character 115): (0) two or more; (1) one (CI = 0.50; RI = 0.50).

In cypriniform fishes and Hiodon alosoides a single epural is present ( Fink & Fink, 1981; Hilton, 2002; Figs 16 , 40, 41). In the remaining outgroup taxa two or more epurals are present. This character is inapplicable to Lefua costata , which lacks an epural.

121. Proximal tip of hypural 1 ( Sawada, 1982: character 48, in part): (0) separate from surrounding hypural and parhypural elements, and autogenous with ural centrum 1 or compound centrum; (1) separate from surrounding hypural and parhypural elements, and separated from compound centrum by a short hiatus; (2) fused to proximal tip of parhypural; (3) fused to proximal tip of parhypural + hypural 2 + compound centrum (CI = 0.5; RI = 0.75).

In members of the Cypriniformes the proximal tip of parhypural 1 is either fused with the proximal tip of the parhypural (the most common condition; Figs 16A–C, D , 40, 41A–C, E–G) or part of a larger element, hypothesized to be the result of fusion between the parhypural, hypurals 1 and 2, and the compound centrum (the condition exhibited by members of the Cobitidae and in the balitorid Annamia normanii ). In P. gracilis , P. robustus , P. melissa , and Homaloptera stephensoni , the proximal tip of hypural 1 is separate from surrounding elements, and is also separated from the compound centrum by a short hiatus, similar to the condition exhibited by members of the order Characiformes and certain members of the Gonorynchiformes ( Fink & Fink, 1981; Figs 16D, E , 41H). In outgroup taxa the proximal tip of hypural 1 is separate from surrounding elements, and is autogenous with ural centrum 1.

122. Hypural 6: (0) present; (1) absent (CI = 0.25; RI = 0.88).

In members of the genus Psilorhynchus , members of the family Balitoridae , all members of the Nemacheilidae (excluding Mesonemacheilus triangularis ), and the out-group taxon Denticeps clupeoides , hypural 6 is absent ( Figs 16 , 40D–F, H). In other cypriniform fishes and the remaining outgroup taxa hypural 6 is present ( Figs 40, 41A–C, G). 123. Hypural 3: (0) proximal tip not fused with associated centrum; (1) proximal tip fused with compound centrum. (CI = 1.00; RI = 1.00).

In members of the family Catostomidae the proximal tip of hypural 3 is fused with the compound centrum ( Fink & Fink, 1981; G. Arratia, pers. comm.; Fig. 41B). In other cypriniform fishes the proximal tip of hypural 3 is autogenous with the compound centrum ( Figs 16 , 40, 41A, C–H). In outgroup taxa the proximal tip of hypural 3 is autogenous with its associated ural centrum ( Greenwood, 1968; Forey, 1973; Arratia, 1997; Hilton, 2002).

SCALES

124. Lateral-line bearing scale size: (0) moderate to large, height of lateral-line bearing scale much greater than height of lateral-line canal ossification; (1) small, height of lateral line bearing scale equal to or shorter than height of lateral-line canal ossification (CI = 0.33; RI = 0.89).

In members of the families Botiidae , Cobitidae , Balitoridae (excluding Homaloptera zollingeri ), and Nemacheilidae , the cycloid scales are small to tiny in size, the height of the lateral-line bearing scales is equal to or shorter than the height of the lateral-line canal ossifications, next to which they appear dwarfed ( Fig. 42B ). In other cypriniform fishes and in outgroup taxa the scales are generally much taller, the height of the lateral-line bearing scales being much taller than the lateral-line canal ossification ( Fig. 42A ), although there are notable exceptions (e.g. in certain North American cyprinids, in which the scales are greatly reduced in size; see Coburn & Cavender, 1992).

125. Anterior radii: (0) present; (1) absent (CI = 0.25; RI = 0.78).

The scales of all species of Psilorhynchus , except P. sucatio , lack anteriorly directed radii ( Fig. 22B–F ), as do the scales of the cyprinids Rhodeus sericeus , Gobio gobio (Linnaeus, 1758) and Zacco cf. platypus . A variable number of anteriorly directed radii are present on the scales of the majority of other cypriniform fishes examined (e.g. as illustrated in P. sucatio ; Fig. 22A ); notable exceptions include the cultrine cyprinid Xenocypris davidi and most North American cyprinids examined, excluding Notemigonus crysoleucas (Mitchill, 1814) ( Cavender & Coburn, 1992; Coburn & Cavender, 1992). All outgroup taxa included for analysis, except for Distichodus antonii , exhibited anteriorly directed radii. It was not possible to determine from the cleared and stained specimens examined whether anteriorly directed radii were ·

present on the tiny scales of Annamia normani , Vaillantella euepiptera , Syncrossus cf. berdmorei Blyth, 1860 , or Yasuhikotakia sidthimunki , which were coded with a ‘?’ for this character.

126. Lateral-line canal ossifications: (0) similar in size and shape along entire length of canal; (1) third and fourth lateral-line canal ossifications much larger than more anterior and posterior ossifications (CI = 1.00; RI = 1.00).

In members of the families Botiidae , Cobitidae , Nemacheilidae, and Balitoridae the lateral-line canal ossifications are not uniform in size and shape along the length of the canal, with the third and fourth ossification being much larger than more anterior or more posterior ossifications ( Fig. 42D ). In other cypriniform fishes and in outgroup taxa the lateral-line canal ossifications are similar in size and shape along the entire length of the canal ( Fig. 42C ). This character is inapplicable to taxa that lack the lateral-line sensory canal.

Figures

Figure 16. Caudal fin skeleton of Psilorhynchus, left side in lateral 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. D, Psilorhynchus robustus, CMK 17941, paratype, 58.1-mm SL. D, P. pseudecheneis, KU 29519, 40.3-mm SL. Cartilage highlighted in grey. Abbreviations: CC, compound centrum; DCRC, distal caudal radial cartilage; *, hypural 5; Ep, eplural; HA, haemal arch; H1–4, hypurals 1–4; HS, haemal spine; NA, neural arch; NS, neural spine; Ph, parhypural; Pls, pleurostyle; PU2–3, preural centra 2–3. Upper- and lowermost principal caudal fin rays are indicated with a black dot.

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.

Figure 42. Scales and lateral line canal ossifications of selected cypriniform fishes, left side in lateral view. A, lateral line scales and adjacent scales dorsal to the anal fin of Carpiodes cyprinus, UAIC 14314.03, 67.5-mm standard length (SL). B, lateral line canal ossification and adjacent scales dorsal to the anal fin of Yasuhikotakia modesta, UAIC 14181.04, 50.4-mm SL. C, schematic illustration of the anteriormost portion of the lateral line canal of Epalzeorhynchos frenatus, UAIC 14180.40, 41.2-mm SL. D, schematic illustration of the anteriormost portion of the lateral line canal of Yasuhikotakia modesta (same specimen as in B), scales omitted. *Enlarged third and fourth lateral line canal ossification in D. Abbreviation: LCO, lateral line canal ossification.