A new genus and species of Labeonini (Teleostei: Cyprinidae) from the Pearl River in China

Zuojiangia jingxiensis, both a new genus and species, is described from the Pearl River in China. It is distinguished from all other genera and species of Labeonini by the unique combination of modified oromandibular structures and head skeleton: a well-developed, pendulous, and conspicuously arched rostral fold, with an entirely crenulated margin; prominent papillae densely covering the margin of the rostral fold and anterior part of the lower lip; long postlabial grooves, partitioning the lower lip into three parts; transverse branch of dentary longer than half the length of the longitudinal branch; stubby lateral process present at the anterolateral margin of the longitudinal branch of the dentary, close to the corner; in the upper jaw, the premaxilla bears a triangular ascending process tapering to a point; maxilla exhibits a pair of articular heads at the anterodorsal margin, and a distinct fingerlike descending process posterior to the medial articular head embracing the ascending process of the premaxilla.


Introduction
The cyprinid tribe Labeonini exhibits a high degree of morphological modification in the oromandibular structures. More than 30 genera of Labeonini are currently recognized, most of which are distributed in China [1,2]. Moreover, the species in the karst regions of southwestern China account for more than half of the genera and species of the Labeonini in China [2]. It can be seen that China exhibits a high species diversity of Labeonini. Recently, several new genera have been established in China, with their validity confirmed by molecular studies [2,3]. The past results of molecular phylogeny in Labeonini were not consistent with those of morphological phylogeny, and the morphological characters do not have systematic significance but can be useful for taxonomy [4].
Guangxi Province is home to the karst regions of southern China, which are characterized by abundant limestone formations and underground rivers, as well as high biodiversity. Since 2000, eleven new species and four new genera of labeonins have been reported from Guangxi PLOS ONE | https://doi.org/10.1371/journal.pone.0199973 July 6, 2018 1 / 14 a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 [4][5][6][7][8][9][10][11][12][13][14]. Three of the new species (Pseudogyrinocheilus longisulcus, Cophecheilus bamen, and Rectoris longibarbus) and one genus (Cophecheilus) are from the Jinxi area in Guangxi [11,13,15], a region known for great fish species diversity. During examination of fish collections from Guangxi, an undescribed genus was discovered. Based on this examination, the oromandibular structure was described and the head skeleton was illustrated using X-ray microtomography. A combination of morphological characters distinguishes the new genus from all other known labeonine genera; hence, a new genus is required, which is described herein.

Measurements and observations
Measurements and counts follow Chu and Chen [16] and Kottelat [17]. The methods used for counting the branched rays of the dorsal and anal fins and lateral line scales are described in Zheng et al. [12]. Vertebrae were counted from radiographs taken by a Digital Cabinet X-ray System (Milford, USA). Osteological characters were scanned using a MicroCT Skyscan 1176 (Bruker, Belgium) with 50 kV tube voltage, 0.3-degree rotation step, and 9-μm pixel resolution, and the cross-sections of each specimen were reconstructed using the associated software. Three-dimensional renderings were created, visualized, and manipulated using VG Studio Max (v2.1) software. By adjusting the gray value threshold, the structure of the bones remained while the soft tissues were virtually removed [18]. Examined specimens are in the collection of the Kunming Institute of Zoology (KIZ), Chinese Academy of Sciences and the Fishery Bureau of Du'an County (FBD). Abbreviations used in the text are: SL, standard length; HL, lateral head length. In addition, a morphological phylogenetic analysis was conducted with maximum likelihood (ML) approach using PAUP Ã 4.0b 10 [19].
We followed all guidelines of the Animal Ethics Committee of the Kunming Institute of Zoology, Chinese Academy of Sciences. All work was approved by the committee and did not involve any endangered species or protected areas (SMKX-2012019).

Nomenclatural acts
The electronic edition of this article conforms to the requirements of the amended International Code of Zoological Nomenclature, and hence the new names contained herein are available under that Code from the electronic edition of this article. This published work and the nomenclatural acts it contains have been registered in ZooBank, the online registration system for the ICZN. The ZooBank LSIDs (Life Science Identifiers) can be resolved and the associated information viewed through any standard web browser by appending the LSID to the prefix "http://zoobank.org/". The LSID for this publication is: urn:lsid:zoobank.org:pub: 56A190D5-AA22-4381-975B-414F97A29354. The electronic edition of this work was published in a journal with an ISSN, and has been archived and is available from the following digital repositories: PubMed Central, LOCKSS. In the new genus, the left dentary is shaped like an inverted L in ventral view ( Fig 3C, right dentary is a mirror image), with the transverse branch being longer than half the length of the longitudinal branch ( Fig 3C). A stubby lateral process is present at the anterolateral margin of the longitudinal branch ( Fig 3C, lp), close to the corner. In the upper jaw, the premaxilla bears a triangular ascending process tapering to a point ( Fig 3D). The maxilla has a pair of articular heads at the anterodorsal margin, and a distinct fingerlike descending process posterior to the medial articular head embracing the ascending process of the premaxilla (Fig 3D, fp mx). There are three rows of teeth on the pharyngeal bone (= ceratobranchial 5, Fig 4). The teeth are coarsely compressed (Fig 4A, 4D and 4G). It is worth noting that the dentition formula was variable among the three examined specimens: 2.4.5-6.4.2 in holotype KIZ2012003910, 2.4.4-5.4.2 in paratype KIZ2012003911, and 2.4.5-5.4.2 in paratype KIZ2012005694. The main row on the right ceratobranchial 5 had six teeth in the holotype (Fig 4C), but four on the left side of one of the paratypes (Fig 4E).

Zuojiangia, new genus
Etymology. Named for Zuojiang River, where the type species was discovered. The gender is feminine.
Remarks. Zuojiangia is distinguished from all other genera of Labeonini except for Cophecheilus, Prolixicheilus, and Parasinilabeo longibarbus by having long postlabial grooves, complete rostral fold, and developed papillae covering the rostral fold and/or lower lip. Although Zuojiangia resembles the above three genera, it can be easily distinguished morphologically ( Fig 5). It is differentiated from Cophecheilus by having no shallow arched, subdistal depression along the margin of the rostral cap (vs. present), margin of the rostral fold crenulated (vs. medially slightly furrowed but non-fimbriate), and 16-18 circumpeduncular scales (vs. [22][23][24][25][26].  Table 1, S1 Description. Morphometric data are listed in Table 1. Body rounded, and caudal peduncle compressed. Highest point of body usually in front of dorsal-fin origin. Head rounded, depth greater than width. Snout moderately rounded, longer than postorbital length. Eye moderately large, in posterior half of head, close to dorsal profile. Largest measured specimen 113.9 mm SL. Three rows of pharyngeal teeth (Fig 4).
Mouth inferior. Rostral fold developed, pendulous, and margin entirely crenulated. Prominent papillae densely covering margin of rostral fold and anterior part of lower lip. Rostral fold covering upper jaw and connected with lower lip around corner of mouth. Upper lip reduced to thin membrane. Lower lip partitioned into one median lobe and two lateral lobes by long postlabial grooves, with median lobe wider than one-third of mouth gape. Lower lip separated from lower jaw by deep groove. Tiny keratinized tubercles present on snout tip, and slightly more obvious in males than females. Two pairs of long barbels. Rostral barbels reaching posteriorly beyond anterior margin of eyes; maxillary barbels reaching posteriorly beyond posterior margin of eyes.
Dorsal fin with 3 soft unbranched rays and 8 (6) branched rays, origin nearer to tip of snout than to caudal-fin base; margin of fin concave. Anal fin with 3 unbranched and 5 (6) branched rays, margin concave, posterior tip not reaching caudal-fin base, but exceeding midway  (2) branched rays, extending posteriorly midway between pectoral-and pelvic-fin origins. Pelvic fin with 8 (2)-9 (4) branched rays, origin posterior to dorsal-fin origin; tip not reaching anal-fin origin, extending posteriorly midway between pelvic-and anal-fin origins. Anus very close to anal-fin origin; distance from anus to anal-fin less than one eye diameter. Caudal fin with 9 + 8 (6) branched rays, forked, upper lobe slightly longer than lower lobe.  Color in preservative. Body dark brown dorsally and laterally, light brown ventrally. Dark stripe along lateral line on flank, ending at caudal-fin base, width equal to two scales. Fin rays black, membrane hyaline.
Color in life. Similar to pattern described for specimens preserved in preservative, but with dark green color, and stripe more obvious (Fig 7).
Etymology. Named for Jingxi, where the type species was discovered. Treated as a noun in apposition.
Distribution. Zuojiangia jingxiensis is presently known only from a karst cave outlet and small connected unnamed stream, which is a tributary of Zuojiang River, in Jingxi County, Guangxi Province, China, draining into the Pearl River.
Habitat. Zuojiangia jingxiensis lived in a karst cave outlet and connected stream, 1-2 m in depth, sympatric with Balitora ludongensis, Cophecheilus bamen, Prolixicheilus longisulcus, Rectoris longibarbus and Yunnanilus jinxiensis.   [21]. Thynnichthys (type species: Thynnichthys thynnoides Bleeker 1852) has a unique mouth morphology different from all other labeonins, and only a thin rostral fold, simple lower lip, no upper lip, no barbels, and wide and terminal mouth [1].   Zuojiangia resembles Cophecheilus, Prolixicheilus, and P. longibarbus within Labeonini, but can be easily distinguished from these three genera based on morphological characters. In addition to the oral morphological characters, Zuojiangia largely differs from Cophecheilus, Prolixicheilus, and P. longibarbus by the osteological characters of the head and jaw. In the new genus, the dentary in the lower jaw is shaped like an inverted L in ventral view (Fig 3C), the transverse branch is longer than half the length of the longitudinal branch (vs. shorter in Cophecheilus, Prolixicheilus, and P. longibarbus) (Fig 3G, 3K and 3O). A stubby lateral process is present at the anterolateral margin of the longitudinal branch (Fig 3C, lp), close to the corner (vs. at the midpoint of the longitudinal branch in Cophecheilus ( Fig 3G); no lateral process in Prolixicheilus ( Fig 3K); and at one third the anterior position of the longitudinal branch in P. longibarbus (Fig 3O)). In the upper jaw, the premaxilla bears a triangular ascending process tapering to a point ( Fig 3D) (vs. slenderer in Cophecheilus ( Fig 3H); dominant, broad with a blunt tip in Prolixicheilus ( Fig 3L); and lacks an obvious ascending process in P. longibarbus (Fig 3P)). The maxilla exhibits a pair of articular heads at the anterodorsal margin, and a distinct fingerlike descending process posterior to the medial articular head embracing the ascending process of the premaxilla (Fig 3D, fp mx) (vs. fingerlike process of the maxilla vestigial in Cophecheilus ( Fig 3H); well-developed and embracing the ascending process of the premaxilla (invisible in the anterior view) in Prolixicheilus ( Fig 3L); and well-developed and articular head of the maxilla rudimentary in P. longibarbus (Fig 3P)).
Thirteen morphological characters are used to construct the phylogenetic tree (S2 Table). The morphological phylogenetic analysis indicated that the new genus is closely related to Cophecheilus bamen and Parasinilabeo longibarbus (Fig 8). The molecular results suggested that Cophecheilus and P. longibarbus were located at the base of the karst group of Labeonini [2]. Based on our morphological analysis and previous molecular results, it is conceivable that the phylogenetic position of Zuojiangia may also be located at the base of the karst group of Labeonini, showing relatively close relationships with Cophecheilusand P. longibarbus.
The specimens of the new genus were preserved in formalin after their collection, and unfortunately the type locality was destroyed in 2013. Therefore, molecular tissue and new specimens from the type locality are no longer available for study. Because its known habitat has been destroyed, the new genus can be considered rare and likely endangered. To identify the evolutionarily significant unit and protect this rare species, it is necessary to describe the new genus as soon as possible. This work is part of our study on the Labeonini in Southwest China. We hope that the discovery and description of new genera and species will arouse social concern and conservation awareness.