Rectoris longibarbus, Zhu, Ding-Gui, Zhang, E & Lan, Jia-Hu, 2012

Zhu, Ding-Gui, Zhang, E & Lan, Jia-Hu, 2012, Rectoris longibarbus, a new styglophic labeonine species (Teleostei: Cyprinidae) from South China, with a note on the taxonomy of R. mutabilis (Lin 1933), Zootaxa 3586, pp. 55-68 : 58-64

Rectoris longibarbus sp. nov. ( Figs. 2 A and 3A)

Holotype. IHB 200808006, 129.6 mm SL, a stream tributary flowing into Zuo–Jiang of Zhu–Jiang (Pearl River) drainage at Jingxi County, Guangxi, South China; J. H. Lan, Aug., 2008.

Paratypes. IHB 200808002, 200808004–5, 3 ex., 65.3–84.5 mm SL, same data as holotype.

Diagnosis. Rectoris longibarbus is distinguished from two other congeneric species, i.e. R. mutabilis and R. posehensis , by the presence of a dumbbell-like (vs. slender) posterior chamber of the gas bladder, almost equal to (vs. twice as long as) the anterior chamber ( Fig. 4 ), and rostral barbels longer (vs. shorter) than eye diameter, with their lengths 21.0–24.7% of HL (vs. 10.2–18.8). It is similar to R. posehensis in having a longitudinal black stripe running along the lateral line on the flank, but further differs from this species in having a slightly papillated posteromedian patch on the median plate of the lower lip (vs. no patch). It is similar to R. mutabilis in the shared presence of a papillated posteromedian patch on the median plate of the lower lip, but further differs from this species in having a longitudinal black stripe running along the lateral line on the flank (vs. stripe absent).

Description. Morphometric data for the four type specimens are summarized in Table 1. Body elongate, slightly compressed, more so toward caudal-fin base, with greatest body depth immediately anterior to dorsal-fin origin, and least caudal-peduncle depth closer to caudal-fin base than to posterior end of anal-fin base. Dorsal head profile slightly convex; ventral head profile straight. Dorsal body profile slightly convex anterior to dorsal-fin origin; straight or slightly convex from dorsal-fin origin to origin of dorsal procurrent caudal-fin rays. Ventral profile of body rounded anterior to anal-fin origin; somewhat concave from anal-fin origin to origin of ventral procurrent caudal-fin rays.

Head relatively small, longer and deeper than width. Eyes small, dorsolaterally placed in posterior half of head; interorbital space wide, somewhat convex. Snout blunt when viewed dorsally, with many tiny tubercles on snout tip and anterior part of lachrymal. Lateral portion of snout with a shallow, oblique furrow running from base of rostral barbel to lateral extremity of rostral fold along anteroventral border of lachrymal. Rostral barbels positioned at anterior end of shallow furrow on lateral portion of snout, longer than eye diameter; maxillary barbels minute, rooted in corners of mouth. Mouth slightly arch-shaped.

Rostral fold or cap crenulated, covered densely with papillae, laterally connected with lower lip at corners of mouth. Upper lip greatly reduced or vestigial, with many tiny papillae arranged in a longitudinal row on upper jaw. Upper jaw bearing a thick, flexible, cornified sheath entirely covered by pendulous rostral fold, and laterally connected with lower lip by a frenum at corner of mouth. Lower lip anteriorly separated from lower jaw by a deep groove. Inner surface and anterior edge of free anterior part of median plate of lower lip densely covered with tiny papillae, regularly arranged in many transverse rows. Median plate of lower lip nearly round with a slightly papillose, round posteromedian patch. Lower jaw bearing a thick, cornified cutting edge.

Dorsal fin with 3 simple and 8* (4) branched rays, last one split to base; last simple ray longer than HL; distal margin slightly concave; origin closer to snout tip than to caudal-fin base. Pectoral fin with 1 simple and 12*(1) or 14 (3) branched rays, equal to or slightly longer than HL; tip of depressed fin extending slightly beyond threefourths to pelvic-fin origin. Pelvic fin with 1 simple and 8*(4) branched rays, slightly shorter than HL; origin posterior to vertical of third dorsal-fin branched ray; tip of depressed fin surpassing anus, not reaching anal-fin origin; pelvic axillary scale long, extending beyond base of last ray. Anal fin with 3 simple and 5*(4) branched rays, last one spilt to base; origin closer to pelvic-fin insertion than to caudal-fin base; distal margin concave. Anus anterior to anal-fin origin, separated from it by one scale. Caudal with 9 + 9 branched rays, deeply forked, upper and lower lobes equal in shape and length.

Scales moderately large; lateral line complete, horizontal, 41*(2), 42 (1) or 43 (1) plus 3 scales on caudal-fin base; 11 predorsal midline scales regularly arranged, smaller than those on flank; 1/2 5/1/4 1/2*(4) scales in transverse row anterior to pelvic-fin insertion; circumpeduncular scales 16*(4). Chest and belly scaled; scales along midventral region smaller than those of its nearby regions; scales on chest embedded beneath skin. Gas bladder bipartite, anterior chamber elliptical or round and posterior chamber stick-like, with both ends slightly enlarged, as long as anterior one ( Fig. 4 A). Pharyngeal teeth triserial, tooth pattern 2,4,5–5,4,2 (IHB 200808002, 127.4 mm SL), with compressed and pointed tips (Fig. 5). Gill rakers sparse, short and small.

Coloration. Top of head grayish; snout, cheek, opercle and subopercle grayish; venter of head yellowishwhite. Ground color of body grayish dorsally and laterally, yellowish-white ventrally. An indistinct longitudinal black stripe, roughly two scales in width, originating at upper extremity of gill opening, extending along lateral line on flank, and ending at middle of caudal-fin base. Each scale on flank with dark chromatophores along exposed portion of its posterior margin forming a dark, crescentic, vertically-elongate mark; marks on scales above longitudinal black stripe more prominent. Dorsal and caudal fins dusky, and dorsal surface of pectoral fins with dark chromatophores on fin rays, more dense on leading ray and posterior part of subsequent anterior fin rays, giving it a dusky appearance. Pelvic and anal fins hyaline.

Sexual dimorphism. No differences were found between males and females

Distribution. Known only from a tributary of the Zuo-Jiang of the Zhu-Jiang drainage at Biaoliang village, Lutong town, Jingxi County, Guangxi Province, South China ( Fig. 6 ).

Habitat and biology. Rectoris longibarbus was collected at a temporary pool of water spilled from a karst cave during the annual rainy season (late June to August) ( Fig. 7 A–B). After the rainy season, this pool dries up until the onset of the next rainy season. Four other species that occur with this species are: Rectoris posehensis ( Lin 1935) Yunnanilus jingxiensis ( Zhu et al. 2009) , Pseudogyrinocheilus longisulcus ( Zheng et al. 2010) , and Cophecheilus bamen ( Zhu et al. 2011) . These species were also found in the other temporary pool of water spilled from a karst cave in Pingjiang Village, Lutong Town during the third author’s 2009 and 2010 field surveys in another tributary of the Zuo–Jiang in Jingxi County, where no specimens of R. longibarbus were collected. Some morphological adaptations of this species to the cave environment are the longer rostral barbels, and longer dorsal, pectoral and pelvic fins compared with those of the two congeneric species ( Table 2 ).

Etymology. The specific epithet, used as a noun in apposition, is made from the Latin word “ longus ” (= long) and “ barbus ” (= barbel), in allusion to the presence of a pair of well-developed maxillary barbels.

for R. mutabilis and R. luxiensis and made in this study for R. luxiensis .

Figures

FIGURE 2. Lateral view of: (A) R. longibarbus, IHB 200808006, holotype, 129.6 mm SL; Guangxi Province: Jinxi County: Zuo-Jiang. (B) R. mutabilis, IHB 8840955, 131.6 mm SL; Guizhou Province: Tongyun County: Yuang-Jiang; (C) R. posehensis, IHB 200808001, 121.9 mm SL; Guangxi Province: Jinxi County: Zuo-Jiang.

FIGURE 4. Ventral view of gas bladder in: (A) R. longibarbus, FIGURE 5. Left side of pharyngeal tooth plate in ven- IHB 200808002, paratype, 127.4 mm SL; and (B) R. mutabilis, tromedial view of R. longibarbus, IHB 200808002, para- IHB 85051839, 98.2 mm SL. Scale bar = 5 mm. type, 127.4 mm SL.

FIGURE 6. Map showing distributions of three species of Rectoris from South China: R. longibarbus (˔); R. mutabilis (●); R. posehensis (․).

FIGURE 7. (A) Temporary pool of water spilled from a karst cave where R. longibarbus was collected and (B) the mouth of this cave.