'Henicorhynchus' thaitui, Nguyen & Ho & Hoang & Wu & Zhang, 2020
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publication ID |
https://dx.doi.org/10.3897/zookeys.965.52751 |
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publication LSID |
lsid:zoobank.org:pub:144E38FC-DDCB-4224-A00E-AC3F14AA1CB9 |
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persistent identifier |
https://treatment.plazi.org/id/0E2614B1-EEBB-4DDE-B883-EAD279245950 |
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taxon LSID |
lsid:zoobank.org:act:0E2614B1-EEBB-4DDE-B883-EAD279245950 |
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treatment provided by |
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scientific name |
'Henicorhynchus' thaitui |
| status |
sp. nov. |
'Henicorhynchus' thaitui sp. nov. Figures 1 View Figure 1 , 2 View Figure 2 , 3 View Figure 3 , 4 View Figure 4
Holotype.
IEBR 105901, 74.3 mm SL; Vietnam: Quang Binh Prov.: Phong Nha-Ke Bang National Park: Khe Lanh Cave (in Son River system in the Gianh River basin): 17°25'41"N, 106°18'31"E, altitude 185 m; collectors: A.T. Ho and N.T. Hoang, 12 August 2011 (deposited in IEBR).
Paratypes.
IHB 2016105895-9, 5 specimens, 80.9-99.5 mm SL; IEBR 105900-04, 4 specimens, 68.8-75.6 mm SL; VU 5905-08, 4 specimens, 76.8-83.4 mm SL; all other data same as holotype (deposited in IHB and IEBR, VU).
Diagnosis.
'Henicorhynchus' thaitui sp. nov. can be distinguished from all congeners by having a whitish pink body in life (vs. white or silvery body with a humeral mark or some longitudinal stripes), smaller (vs. larger) eyes (diameter less than vs. greater than maxillary barbel length) and maxillary barbel longer (vs. shorter) than rostral barbel. 'Henicorhynchus' thaitui , along with H. horai (Bănărescu, 1986) and H. inornatus (Roberts, 1997), is further distinct from all other congeners in having 9 (vs. 8) branched dorsal-fin rays. Along with H. horai , it differs from all other congeners in the presence of rostral barbels (vs. absent) and 39-41 (vs. 34-36) lateral-line scales. 'Henicorhynchus' thaitui differs from H. horai and H. inornatus in the presence of two (vs. one) pairs of maxillary and rostral barbels (vs. only the maxillary barbel in H. inornatus and only the rostral barbel in H. horai ); from H. horai in having fewer vertebrae (34 vs. 38-41), and a laterally compressed body (vs. cylindrical in H. horai ); and from H. inornatus in having 39-40 (vs. 35 in H. inornatus ) lateral-line pored scales, and in the absence of a humeral mark (vs. present in H. inornatus ).
Description.
Measurements and meristics of the type series are provided in Table 1 View Table 1 . See Figs 1 View Figure 1 , 2 View Figure 2 for general appearance, Fig. 3a View Figure 3 for lateral and ventral views of the head, and Fig. 4 View Figure 4 for morphology of the oromandibular structures. Body elongate and laterally compressed. Dorsal profile of body from tip of snout to dorsal-fin origin slightly convex. Predorsal profile of body convex, without distinctive hump behind head. Postdorsal profile of body slightly concave. Ventral profile of body from tip of snout to anal-fin origin convex; slightly concave from anal-fin origin to origin of ventral procurrent caudal-fin rays.
Head small, conical, longer than deep, deeper than wide. Eye relatively small, positioned laterodorsally in anterior half of head and considerably behind or above rictus, not visible when head viewed ventrally; diameter less than maxillary-barbel length. Interorbital space slightly convex. Snout slightly pointed in lateral view and broadly rounded in ventral view (Fig. 3a View Figure 3 ). Nares longitudinal and located closer to orbit than to tip of snout and covered by a flap originating from anterior end. Two pairs of long barbels; maxillary barbel much longer than rostral barbel, extending to posterior margin of orbit or beyond, and rostral barbel extending beyond nostrils but not reaching to anterior margin of orbit. Mouth inferior and slightly arched.
Rostral cap well-developed, overhanging, but covering median part of upper lip base; slightly crenulated, laterally attached to root of maxillary barbel and separated from lower lip. Upper lip well-developed, greatly enlarged, separated from upper jaw, covered with papillae; laterally continuous with lower lip around corners of mouth. Upper jaw bearing a thin, flexible horny sheath on cutting margin. Lower lip anteriorly separated from lower jaw by a deep, transversally arched groove; posteriorly confluent with mental region and covered with papillae. Post-labial groove extended anteromedially, but not meeting its counterpart at midline. Lower jaw bearing a thin horny sheath on cutting margin (Fig. 4 View Figure 4 )
Dorsal fin with 3 unbranched and 9 branched rays, last one split to base; last unbranched ray flexible, without serrations along posterior border; distal margin strongly concave; origin midway between snout tip and caudal-fin base or anterior to pelvic-fin insertion. Pectoral fin short, with 1 unbranched and 11 branched rays; tip of adpressed fin not reaching pelvic-fin insertion. Pelvic fin falcate, with 1 unbranched and 8 branched rays; inserted halfway from pectoral-fin insertion to anal-fin origin; tip of adpressed fin extending to vent. Anal fin with 3 unbranched and 5 branched rays; distal margin slightly concave; origin equidistant between pelvic-fin insertion and caudal-fin base. Caudal fin with 9/8 principal rays, deeply forked; upper and lower lobes nearly equal in length.
Scales moderately large. Lateral line complete with 39 (12*) or 40 (2) pored scales, extending along mid-lateral body from upper gill-opening extremity to middle of caudal fin. Predorsal scales 14 (10*) or 15 (3). Scales in transverse row before pelvic fin 5 (3) or 6 (12*) above lateral line and 4 (14*) below. Circumpeduncular scales 16 (14*). Gill rakers on left side of first gill arch 37-39 (2) (Fig. 3b View Figure 3 ). Pharyngeal teeth in 3 rows: 2.4.5-5.4.2 (IHB 2016105898, paratype, Fig. 3c View Figure 3 ). Air bladder bipartite (Fig. 3d View Figure 3 ). Intestines long, thin and highly coiled (Fig. 3e View Figure 3 ). Vertebrae 4+34-35=38-39 (2).
Coloration.
In freshly caught-individuals, body white to pinkish or pale pink with all fins translucent (Fig. 2 View Figure 2 ). In captivity, body pale pink but dorsum turning to pale brown hue in adults exposed to light, becoming gray dorsally within several hours when exposed to daylight (Fig. 1b View Figure 1 ). In alcohol-preserved specimens, body uniformly pale yellow, with all fins light gray, particularly in distal portion (Fig. 1a View Figure 1 ).
Etymology.
The specific name is a noun in the genitive case, honoring Nguyen Thai Tu, ichthyologist from Vinh University, who has contributed considerably to the taxonomy of freshwater fishes in Vietnam.
Troglomorphic characters.
'Henicorhynchus' thaitui sp. nov. presents a mixture of characters characterizing hypogean and epigean fish species. The absence of pigmentation, reduced eye size, and well-developed barbels are troglomorphic characters observed in ' H. ' thaitui . The pale pink or white to pinkish body is shared with hypogean fish species. The eyes are smaller than in congeneric epigean species, but not vestigial or absent as is common in hypogean fish species. The barbels are longer and thicker compared with all congeneric epigean species, but in this regard similar to hypogean fish species.
Distribution and habitat.
'Henicorhynchus' thaitui sp. nov. is known only from the Khe Lanh Cave where it inhabits shallow to deep (0.2-0.8 m) cave streams and pools about 800-1000 m from the cave entrance (Figs 5 View Figure 5 , 6 View Figure 6 ). This cave is located approximately 25 km south of Phong Nha village in the Son Trach commune. It has a length of 1-2 km, completely without light, with a mixed substrate of mud and sands. The type series of ' H. ' thaitui was collected in August 2011, roughly 1 km from the cave entrance. At least 50 individuals of various sizes were observed in streams and pools, 14 of which were caught by hand net (Fig. 7 View Figure 7 ). The fishes were swimming slowly and haphazardly, rather close to the water surface; they swam deeper when disturbed. A new shrimp species ( Do and Nguyen 2014) and the labeonine fish species Speolabeo hokhanhi were recently discovered in the Hang Va Cave, 3-5 km away from the Khe Lanh Cave ( Nguyen et al. 2018).
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