Mustura arenaria Lyu, Lin & Chen 2026, sp. nov.

Mustura arenaria Lyu, Lin & Chen sp. nov. Holotype. SEABRI 20164206, male, 29.3 mm SL, Yaw Stream, a tributary of Yebya River at Pakokku City, Magway Region, Myanmar, 21°26'24.86"N, 94°31'5.21"E, 142 m asl., Xiao-Yong Chen, Tao Qin, Shu-Sen Shu, Khin Mar Mint & Thinn Su Tin, 22 Dec. 2016. Paratypes. SEABRI 20164207, 1 ex., 25.8 mm SL, same as holotype. SEABRI 20170634 –38, 42–44, 48, 50, 52, 56, 12 ex., 27.7–39.5 mm SL, Myan Aww Stream, a tributary of the Chindwin River at Larboh village, Alaungdaw Kathapa National Park, Sagaing Region, Myanmar, 22°34'53.46"N, 94°30'51.84"E, 169 m asl., Xiao-Yong Chen, Tao Qin, Shu-Sen Shu, Paing Zaw & Ye Yint Tun, 21 June 2017; SEABRI 20170752 –53, 2 ex., 34.4–36.8 mm SL, Salin Stream at Nwetamal Village, Sinbyugyun Town, Salin Township, Magway Region, Myanmar, 20°39'44.58"N, 94°41'13.98"E, 58 m asl., Xiao-Yong Chen, Tao Qin, Shu-Sen Shu, Paing Zaw & Ye Yint Tun, 24 June 2017; SEABRI 20170522, 1 ex., 30.3 mm SL, Lower Yemar River, about 10 km upstream of Monywa, Sagaing Region, Myanmar, 22°8'59.64"N, 95°3'26.10"E, 76 m asl., Xiao-Yong Chen, Tao Qin, Shu-Sen Shu, Paing Zaw & Ye Yint Tun, 19 June 2017; KIZ-PZ 20180138, 1 ex., 31.2 mm SL, Nam Sa Pi Stream at Htamanthi, Sagaing Region, Myanmar, 25°21'33.84"N, 95°20'43.32"E, 127 m asl., Paing Zaw & Nay Htet Naing, 8 May 2018; SEABRI 20192385, 1 ex., 29.9 mm SL, Lae Pon Stream, Indawgyi Lake, Kachin State, Myanmar, 25°2'55.72"N, 96°21'1.70"E, Thinn Su Tin & Lamin Ko Ko, 12 May 2019. Non-types. SEABRI 20170639 –41, 45–47, 49, 51, 53–55, 57–63, 18 ex., 28.4–33.4 mm SL, Myan Aww Stream, a tributary of Chindwin River at Larboh village, Alaungdaw Kathapa National Park, Sagaing Region, Myanmar, 22°34'53.46"N, 94°30'51.84"E, 169 m asl., Xiao-Yong Chen, Tao Qin, Shu-Sen Shu, Paing Zaw & Ye Yint Tun, 21 June 2017. Diagnosis. Mustura arenaria is distinguished from its congeners by the following combination of characters: 7–15 lateral blotches alternating with 9–17 saddles, distinctly narrower than interspaces; blotches more elongated in females and more rounded in males; two dark stripes extending from snout tip to the anterior dorsum of eye, forming an “ X ” pattern, but not fused; a pair of blotches surrounding the fontanel, extending from posterior dorsal of eye to nape, and forming a triangle marking; 8 ½ branched dorsal-fin rays; 8 + 8 branched caudal-fin rays; lateral line complete; axillary pelvic lobe present; upper lip with a small notch. Description. See Fig. 1 for general appearance and Table 1 for morphometric data. Body moderately elongated, deepest body depth slightly anterior to dorsal-fin origin, with depth gradually decreasing from dorsal-fin origin to caudal-fin base. Body rounded to slightly compressed anteriorly, compressed posteriorly. Head depressed, dorsal profile arched, decreasing markedly anterior to eye. Snout slightly pointed. Interorbital area wide and flat. Eye oval, near top of head, not visible in ventral view. Cheeks not swollen. Caudal peduncle 1.0–1.7 times longer than deep. Low dorsal and ventral keels present posteriorly on caudal peduncle. Largest recorded size 39.5 mm SL. Dorsal-fin rays iii- 8 1 / 2, distal margin truncated, extending beyond vertical through anus but not reaching anal-fin origin. Pectoral-fin rays i- 9–10, slightly falcate, reaching beyond two-thirds of distance between origin pectoral and pelvic fins, second branched ray longest. Pelvic-fin rays i- 6, reaching close to or through anus, origin opposite of the first or second branched dorsal-fin ray. Axillary pelvic lobe present. Anus situated about twice eye diameters in front of anal-fin origin. Anal-fin rays ii- 5 1 / 2, distal margin truncated, origin closer to caudal-fin base than pelvic-fin origin. Caudal-fin rays 8 + 8, forked, lower lobe slightly longer than upper, longest ray 1.3–1.7 times length of median rays. Body entirely covered by scales, absent between base of pectoral fins and belly in front of pelvic-fin. Lateral line complete. Cephalic lateral line system with 6–9 supraorbital, 3 + 8–13 infraorbital, 6 preoperculo-mandibular, and 3 supratemporal pores. Tubercles present on barbels, dorsal head, and dorsal side of branched pectoral-fin rays. Mouth inferior, small, strongly arched, gape about twice as wide as long (Fig. 2 a). Nostrils adjacent, anterior one on front side of a flap-like tube, not reaching eye. Lips thick and deeply furrowed; upper lip slightly notched medially; lower lip deeply interrupted medially, forming two triangular pads. Processus dentiformis week. Lower jaw without median notch. Three pairs of elongate barbels. Inner rostral barbel reaching close to or through anterior margin of eye; outer one reaching close to or surpassing posterior margin of eye. Maxillary barbel reaching through posterior margin of eye. Two halves of air bladder capsule connected by a manubrium; posterior chamber free, small, unossified (Fig. 2 c). Intestine with a small bend (Fig. 2 e). Vertebral count 4 + 28–29 (n = 2) (Fig. 1 i). Coloration. In life: Body translucent. Dorsal and lateral sides of body light brown, ventral silvery. Saddles and blotches dark brown. Dorsal and lateral head with black blotches. Snout tip light brown, dark around nostrils. Barbels brownish. All fin membranes hyaline. Dorsal-fin and caudal-fin rays gray. Preserved in 10 % formalin. Head and body pale whitish to yellowish. Body with 7–15 vertically elongated lateral blotches, narrower than interspaces, anterior more elongated, alternating with 9–17 saddles. Lateral blotches more rounded in males. Basal caudal bar dissociated and faint, forming an upper small spot (usually absent) and a lower elongated blotch. Two dark stripes extending from snout tip to dorsum of anterior nostrils, not connected; a pair of small faint blotches between dorsal nostrils, forming an “ X ” - shaped pattern together with stripes. A pair of elongated blotches in interorbital space. A pair of blotches surrounding fontanel from posterior dorsal eye to nape, forming a triangle mark (Fig. 2 b). Ventral side of head yellow, more intense on gill arches. Dorsal-fin membranes hyaline, with 1–2 rows of faint spots on branched rays. Pectoral, pelvic, and anal-fin rays hyaline. Caudal fin hyaline to grayish. Barbels white, bearing a few scattered melanophores dorsally. Sexual dimorphism. Males with a longer and stretched downward suborbital flap with small tubercles (Fig. 3 c); females with either a small suborbital flap, groove, or lacking it (Fig. 3 a, b). In males, first branched pectoral-fin ray wider and slightly upward, without membrane between branches except near tip (Fig. 2 d). Lateral blotches more elongated in females (Fig. 1 e – h), and more rounded in males (Fig. 1 a – d). Tubercles on snout, dorsal and lateral sides of head more developed in males. Etymology. The specific epithet “ arenaria ” is derived from the Latin word “ arena ” (meaning “ sand ”), feminine in gender, in reference to the species’ preference for sandy substrate habitats. The Chinese name is suggested as 沙迷鳅. Habitat. Mustura arenaria was observed in the Chindwin-Irrawaddy River drainage. It prefers flowing water in streams with fine sandy substrates and occurs in small aggregations (Fig. 4). Sympatric species recorded at type localities include: Anguilla bengalensis (Gray, 1831), Pangio signicauda Britz & Maclaine, 2007, Schistura callidora Bohlen & Šlechtová, 2011, Opsarius barnoides (Vinciguerra, 1890), Hypsibarbus oatesii (Boulenger, 1893), Pethia stoliczkana (Day, 1871), Glyptothorax ngapang Vishwanath & Linthoingambi, 2007, G. trilineatus Blyth, 1860, and G. burmanicus Prashad & Mukerji, 1929. Distribution. Mustura arenaria is currently known from the Chindwin-Irrawaddy River drainage, including Indawgyi Lake (Fig. 5). It is expected to spread more widely throughout tributaries of the Irrawaddy basin in central Myanmar, particularly in the dry zone of the Sagaing, Mandalay, and Magway regions. Phylogenetic analysis. The ILD test revealed no significant conflict between the Cyt b and RAG 1 genes (p = 0.335). The genus Mustura was recovered as polyphyletic in the phylogenetic analyses constructed from Cyt b, RAG 1, and combined datasets, respectively. These results also strongly supported the distinct species status and monophyly of the new species, M. arenaria sp. nov. However, a single gene contains only a limited amount of phylogenetic information. The topological structures of the two single-gene trees differed markedly from those of previous studies and were weakly supported (Suppl. material 1: figs S 1, S 2). Conversely, the phylogenetic analysis based on the combined dataset was consistent with previous findings (Fig. 6). Consequently, the discussion herein is based on the analysis of the combined data. The K 2 P genetic distance based on Cyt b between M. arenaria and its congeners ranged from 13.49 % to 16.16 %. The minimum K 2 P distance (9.46 %) was observed between Mustura sp. UF 192977 and M. yangi, whereas the maximum distance (18.57 %) was found between Mustura sp. Magway and M. geisleri. The intraspecific genetic distance within M. arenaria was 1.19 % (Table 2). Comparisons Species of Mustura can be divided into two groups based on whether the lateral line is complete or incomplete. Mustura arenaria, together with M. bella, M. celata, M. chindwinensis, M. daral, M. harkishorei, M. maepaiensis, M. prashadi, M. shanensis, M. shuensis, M. subhashi, M. taretensis, M. tigrina, M. tuivaiensis, M. yangi, M. yunnaniloides, M. isostigma, and M. shuangjiangensis, belongs to the complete lateral-line group. A detailed comparison of diagnostic characters among Mustura species is provided in Table 3. Within the complete lateral-line group, M. arenaria can be readily distinguished from species with continuous lateral bars by having 7–15 lateral blotches alternating with 9–17 dorsal saddles. The lateral color patterns of these species are as follows: 12–30 bars, occasionally separated by a dist