Oreonectes platycephalus Günther 1868

(Figs. 1, 3A, 5–6, Table 1)

Oreonectes platycephalus: Günther, 1868: 369; Zhu & Cao, 1987: 326; Zheng, 1989: 46; Zhu, 1989: 23; Ye in Pan et al., 1991: 245; Lan et al., 1995: 367; Zhu, 1995: 107; Kottelat, 2001: 46; Prokofiev, 2005: 431; Zhang et al., 2006: 614; Du et al., 2008: 29; Yang et al., 2011: 211; Kottelat, 2012a: 346; Kottelat, 2012b: 94; Kottelat, 2013: 202; Zhang et al., 2016: 130; Deng et al., 2016b: 146; Deng et al., 2016a: 55; Gan et al., 2017: 32; Huang et al., 2020: 117; Yu et al., 2023: 93; Luo et al., 2024: 294.

Homaloptera (Octonema) rotundicauda: Martens, 1869: 608.

Lefua hoffmanni: Herre, 1932: 429; Böhlke, 1953: 40; Prokofiev, 2005: 437; Kottelat, 2012b: 87.

Oreonectes yenlingi: Lin, 1932: 380.

Diagnosis. Oreonectes platycephalus (including the holotype and paratype of Lefua hoffmanni) is distinguished from other species of Oreonectes by the following combination of characters: eye small, positioned on dorsolateral surface of head; dorsal fin origin posterior to pelvic fin origin; maxillary barbel reaching gill cover (preopercle) when extended; body covered by scales except for head; absence of a dark brown lateral stripe on both body sides; single dark brown vertical bar at caudal fin base; caudal fin rounded; dorsal fin rays iii, 6; pectoral fin rays i, 9–11; pelvic fin rays i, 7; anal fin rays iii, 5-6; 5–6 supraorbital pores; 4 + 9–11 infraorbital pores; 7–9 preoperculo-mandibular pores; abdominal vertebrae 17–19; caudal vertebrae 17–19.

Description. Counts and measurements of the syntypes are listed in Table 1. The specimens are damaged, quite soft, and uneasy to handle.

Body elongated, cylindrical, and rounded anteriorly to slightly compressed posteriorly. Body depth slowly increasing up from occiput to dorsal fin origin. Behind dorsal fin, body depth about equal to caudal fin base. Dorsal profile with shallow concavity between head and body. Lateral head length less than one-fourth of SL. Head dorsoventrally compressed. Interorbital area flattened. Snout rounded in dorsal view. Eye small, positioned on dorsolateral surface of head. Mouth subterminal; inferior, slightly arched. Lips fleshy and smooth. No median incision in upper lip. V-shaped median notch in lower lip. Inner rostral barbel short, reaching about to corner of mouth when extended; outer one reaching past posterior border of eye when extended. Maxillary barbel reaching gill cover (preopercle) when extended. Nostrils separated from each other; anterior nostril formed as long nasal barbel; posterior opening larger than anterior one; anterior nostril at anterior side of a nasal barbel, close to base. Nasal barbel reaching about to anterior border of eye when extended. Small dorsal and ventral adipose keels. Caudal peduncle 1.2–1.5 times longer than its depth (depth including keels). Body covered by scales except for head. Lateral line incomplete, with about 6–15 pores (difficult to count with accuracy). Dorsal fin rounded. Origin of dorsal fin nearer to caudal fin base than to tip of snout; dorsal fin origin posterior to pelvic fin origin. Pectoral fin horizontal. Anal fin rounded. Anus positioned slightly anterior to anal fin. Caudal fin rounded.

Cephalic lateral line system with 5–6 (modally 6) supraorbital, 4 + 9–11 (modally 4 + 10) infraorbital, 7–9 (modally 7) preoperculo-mandibular, and 3–4 (modally 3) supratemporal pores.

Caudal skeletal system composed of first and second preural centra, 4–5 hypurals (modally 5), haemal spine and arch, parhypural, pleurostyle, and free epural; uroneural absent (opisthural cartilage no visible).

Color in 70% ethyl alcohol. Body and head pale brown, with single dark brown vertical bar at caudal fin base. All fins pale to transparent without speckles.

Remarks. Günther (1868) described the collection locality of the syntype of Oreonectes platycephalus as “from a small stream near the top of HongKong Mountains (?), 15,000 feet above the level of the sea.” However, there are no mountains in Hong Kong with an elevation of 15,000 feet, and it is highly likely that this is an error, possibly meant to be 1,500 feet, although further research is required in this regard.

Oreonectes polystigmus Du, Chen &Yang 2008 shares morphological similarities with Oreonectes platycephalus (Du et al., 2008). According to Du et al. (2008), O. polystigmus can be distinguished from O. platycephalus by the following characteristics: cephalic lateral line system with 7 supraorbital pores (vs. 8 in O. platycephalus); 4 + 7 infraorbital pores (vs. 3 + 10); lateral line with 6–8 pores (vs. 16–18); body with many different spots (vs. body plain); posterior portion of air-bladder developed, filling the body cavity (vs. reduced, reaching the vertical of the pectoral-fin base). However, in the syntypes of O. platycephalus, the number of supraorbital pores is 5–6, the number of infraorbital pores is 4 + 9–11, and the number of lateral line pores is about 6–15, which differ from the characteristics described for O. platycephalus by Du et al. (2008). The number of supraorbital pores and infraorbital pores in the syntypes of O. platycephalus differs from the counts provided by Du et al. (2008) for O. polystigmus, possibly representing diagnostic characteristics for both species (i.e., the number of supraorbital pores 7 in O. polystigmus vs. 5–6 in O. platycephalus, and infraorbital pores 4 + 7 vs. 4 + 9–11). Although the number of lateral line pores of the syntypes of O. platycephalus was difficult to count with accuracy, there were no differences in the number of lateral line pores between O. polystigmus as reported by Du et al. (2008) and the syntypes examined in this study. As such, this characteristic is not considered as diagnostic.

Oreonectes damingshanensis Yu, Luo, Lan, Xiao & Zhou 2023 is similar to Oreonectes platycephalus in its morphological characteristics (Yu et al. 2023). Yu et al. (2023) provided diagnostic characteristics for both species as follows: number of branched dorsal fin rays (7 in O. damingshanensis vs. 8 or 9 in O. platycephalus); number of branched pectoral fin rays (9 vs. 11); number of branched pelvic fin rays (7 vs. 8); number of anal fin rays (iii, 5 vs. ii, 6 or 7); number of inner gill rakers on first gill arch (9 vs. 14 or 15); length of maxillary barbel (not reaching the posterior margin of the gill cover vs. reaching the posterior margin of the eye). Among these characters, the number of branched dorsal fin rays (6 in the syntypes of O. platycephalus), the number of branched pelvic fin rays (7), and the number of anal fin rays (iii, 5–6) differ between the characteristics of O. platycephalus as described by Yu et al. (2023) and those observed in the syntypes of O. platycephalus in this study. The number of branched dorsal fin rays in the syntypes of O. platycephalus differs from the counts provided by Yu et al. (2023) for O. damingshanensis, possibly representing diagnostic characteristic for both species (i.e., the number of branched dorsal fin rays 7 in O. damingshanensis vs. 6 in O. platycephalus). Because no differences were apparent in the number of branched pelvic fin rays and the number of anal fin rays between the syntypes of O. platycephalus and O. damingshanensis, these characteristics are not considered as diagnostic.

All specimens examined in this study (including the holotype and paratype of Lefua hoffmanni) possess an epural. Sawada (1982) and Prokofiev (2005) noted that the loss of the epural was considered a synapomorphy of Lefua. The present investigation also confirmed that the presence or absence of the epural is a diagnostic characteristic between Oreonectes and Lefua.