Microdous hanlini (Gobiiformes: Odontobutidae), a new species of the fine-toothed sleepers from Guangxi, China Author Wang, Fangxin Shanghai Universities Key Laboratory of Marine Animal Taxonomy and Evolution, Shanghai Ocean University, Shanghai 201306, China & Engineering Research Center of Environmental DNA and Ecological Water Health Assessment, Shanghai Ocean University, Shanghai 201306, China Author Wei, Mulan Du’an Yao Autonomous County Aquatic Technology Station, Hechi, Guangxi 530700, China. Author He, You Shanghai Synchrotron Radiation Facility, Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201204, China. Author Li, Chenhong Shanghai Universities Key Laboratory of Marine Animal Taxonomy and Evolution, Shanghai Ocean University, Shanghai 201306, China & Engineering Research Center of Environmental DNA and Ecological Water Health Assessment, Shanghai Ocean University, Shanghai 201306, China text Zootaxa 2024 2024-07-09 5477 3 367 379 http://dx.doi.org/10.11646/zootaxa.5477.3.6 journal article 10.11646/zootaxa.5477.3.6 1175-5326 12732998 41523CF9-C99B-490D-BB77-3336A59D1E07 Microdous hanlini Wang, He & Li , sp. nov. Holotype . SOU1801015–8 , female , 112.0 mm standard length (SL). Holotype obtained from a river of Du’an ( 23°55.94′N , 108°6.07′E ), Guangxi , China ; collected by J.-H. Lan , March 2020 ( Fig.2 ) . Paratypes . SOU1801015–7, male, 84.3 mm SL; SOU1801015–1, male, 76.4 mm SL; SOU1801015–4, female, 82.3 mm SL; SOU1801015–3, male, 60.3 mm SL. Collection data same as for the holotype . Etymology. The species name is named after Prof. Hanlin Wu in honor of his significant contributions to the study of the gobiiform fishes of China . Diagnosis. The species M. hanlini can be distinguished from M. chalmersi ( Nichols & Pope, 1927 ) by the following characteristics: wider head, head width/head length = 0.51–0.58 (vs. slender head, head width/ head length = 0.48–0.53); wider interorbital width, interorbital width (bone)/head length = 0.15–0.19 (vs. slender head and narrow interorbital width, interorbital width (bone)/head length = 0.09–0.13). The species can be distinguished from M. amblyrhynchos by the following characteristics: snout pointed, snout length/head length ratio 0.29–0.35 (vs. blunt snout, snout length/head length ratio 0.26–0.28); slenderer head, head width/ head length = 0.51–0.58, (vs. head width/ head length =0.61–0.65); eye large and protruding outward (vs. eye not protruding) ( Fig. 3 , Table 1 ). The species M. hanlini can be distinguished from Sineleotris saccharae by absence of dark band under eye. The species M. hanlini can be distinguished from Sineleotris namxamensis by the following characteristics: lateral scale rows 40-43 (vs. 36-39); transverse scale rows 14-16 (vs. 12-14). These distinguishing features showed no difference between male and female individuals of M. hanlini ( Table 2 ). FIGURE 2. Microdous hanlini sp. nov. , SOU1801015–8, holotype, 112.0 mm standard length, Du’an, Guangxi. A lateral B ventral C dorsal. Description. First dorsal fin VIII or VIIII; second dorsal fin I, 9–11; anal fin I, 7–9; pectoral fin rays 13–15; pelvic fin I, 4–5; caudal fin rays 14–16; longitudinal scale rows 40–43; transverse scale rows 14–16; predorsal scales 18–23 ( Table 2 ). Body stout, cylindrical front, slightly compressed posteriorly. Head medium large and blunt, height of the head equal to the width of the head. Eye large and protruding. Anterior end of the eye behind the posterior one-third of the upper jaw. Gill openings extending to under front part of eyes. Gill rakers thin and pointed. Cephalic sensory canals complete. Nostrils separated, two on each side, anterior nostril with a short tube, posterior nostril rounded, both located in front of the eye. Smooth or tiny teeth–like dermal projections in vomerine region ( Fig. 4 ). The origin of the first dorsal fin aligned with or slightly posterior to the origin of pelvic fin. The second dorsal fin originates before the origin of the anal fin. Caudal and pectoral fins oval. Pelvic fins separated, posterior ends not reaching anus. Lateral lines absent, body surface and opercula covered with weakly ctenoid scales. The body color of formalin-fixed specimens is grayish brown, with light-colored ventral surface, multiple dark spots on the dorsal fins, caudal fin and lateral surface of the body, and an irregular black spot on the upper base of the pectoral fins ( Fig. 2 ). FIGURE 3. Lateral head ( A ) and dorsal ( B ) view of Microdous chalmersi (top, SL 83.0 mm, SOU 76V8792, Holotype), M. hanlini sp. nov. (middle, SL 84.3 mm, SOU1801015–7, Paratypes) and M. amblyrhynchos (bottom, SL 74.9 mm, SOU1801010– 7, Holotype) FIGURE 4. Vomerine region of A Microdous hanlini sp. nov. SOU1801015_10; B M. hanlini SOU 1801015–2; C M. chalmersi SOU 1801009–1. Abbreviation: vt, vomerine teeth–like dermal projections. TABLE 1. Comparison of measurements of Microdous hanlini sp. nov. vs M. chalmersi and M. amblyrhynchos .

Species	Microdous hanlini		M. chalmersi		M. amblyrhynchos
Specimen	SOU1801015 - 1	SOU1801015 - 2	SOU1801015 - 3	SOU1801015 - 4	SOU1801015 - 5	SOU1801015 - 6	SOU1801015 - 7	SOU1801015 - 8	70504	v 8791	v 9228	832384	v 8792	SOU1801010 - 7	SOU1801010 - 8	SOU1801010 - 1	SOU1801010 - 2	SOU1801010 - 3
Percentage of head length (%)
Maximum head width	52.17	51.95	57.34	55.09	58.34	56.06	51.36	58.01	48.86	49.23	53.33	48.34	49.60	60.98	62.73	64.87	57.95	62.16
Interorbital width	14.75	18.74	17.47	16.81	16.77	18.58	14.87	15.39	8.67	11.92	13.33	12.31	9.73	26.78	26.2	27.23	26.92	26.13
Snout length	30.97	33.15	35.27	28.8	34.09	31.40	30.75	34.24	31.45	34.17	39.59	31.07	33.30	26.39	27.33	27.32	27.78	27.03
Percentage of head width (%)
Interorbital width	53.28	49.78	46.45	61.97	52.99	58.76	62.25	48.15	37.93	42.39	45.03	47.75	47.16	41.97	46.46	42.03	43.93	41.77

TABLE 2. Morphological characters of the eight specimens of Microdous hanlini sp. nov.

Characters	SOU 1801015 - 1 female	SOU 1801015 - 2 male	SOU 1801015 - 3 female	SOU 1801015 - 4 male	SOU 1801015 - 5 female	SOU 1801015 - 6 male	SOU 1801015 - 7 female	SOU 1801015- 8 male
Counts
Dorsal fins	VIII, I–9	VIII, I–9	VIII, I–9	VIII, I–9	VIII, I–9	VIII, I–9	VIIII, I–9	VIII, I–11
Anal fin	I–8	I–7	I–8	I–7	I–8	I–8	I–8	I–9
Pectoral fin rays	13	14	14	14	14	14	14	15
Pelvic fin	I–5	I–5	I–5	I–5	I–4	I–5	I–5	I–5
Caudal fin rays	15	15	14	15	15	16	16	15
Lateral scale (rows)	41	40	42	40	41	40	40	43
Transverse scale (rows)	15	16	15	15	15	15	14	15
Predorsal scales	20	22	20	22	23	21	22	18
Measurements (mm)
Total length	76.4	115.1	112.3	82.3	82.5	80.3	84.3	111.8
Standard length	59.3	97.9	103.4	70.7	70.8	67.0	71.0	93.8
Preanal length	37.5	60.4	60.3	39.9	42.2	40.8	43.8	53.6
Caudal peduncle length	17.9	27.5	25.7	18.2	19.3	17.6	18.2	28.2
Caudal peduncle depth	5.1	9.5	10.2	6.5	6.7	6.8	6.4	9.3
Length of first dorsal fin base	7.37	12.3	12.13	8.25	9.1	9.53	9.57	13.34
Length of second dorsal fin base	9.5	18.1	17.7	11.6	10.8	11.6	12.1	18.5
Length of anal fin base	6.2	10.7	11.2	8.7	7.7	7.8	7.7	12.1
Body depth at caudal fin base	5.8	10.3	9.00	8.2	6.6	7.2	7.2	10.3
Pectoral fin length	11.7	23.3	22.2	15.7	14.0	14.3	16.8	21.9
Pelvic fin length	12.9	17.2	19.3	12.0	13.5	11.4	12.7	16.3
Body depth at first dorsal fin origin	11.4	18.0	17.8	12.6	13.6	11.9	13.9	16.4
Body depth at anal fin origin	8.2	15.7	16.9	10.8	9.4	10.4	11.2	15.4
Body width at first dorsal fin origin	8.6	14.5	14.7	10.1	10.6	9.3	10.5	14.8
Body width at anal fin origin	4.5	10.2	9.7	6.7	7.7	7.6	6.1	11.5
Head length	19.9	35.7	33.9	22.7	22.1	21.4	24.6	29.8
Postorbital head length	10.1	19.6	16.1	11.8	10.8	10.8	11.5	13.5
Maximum head width	10.4	18.5	19.5	12.5	12.9	12.0	12.6	17.3
Maximum head depth	10.2	17.5	18.9	13.5	11.6	11.6	12.6	17.5
Head depth at preopercle	7.9	14.8	15.3	10.9	8.8	8.9	10.2	14.5
Snout length	6.2	11.8	12.0	6.5	7.5	6.7	7.6	10.2
Eye diameter	5.5	6.7	6.6	5.0	5.5	4.6	5.1	6.6
Interorbital width	2.9	6.7	5.9	3.8	3.7	4.0	3.7	4.6
Lower jaw length	7.1	11.4	10.2	7.7	7.2	7.3	7.9	9.1

Coloration in life. Head brown with black dots on cheek. Body side dark brown with irregular black spots. Abdomen dark. Fins dim and transparent, with banded black spots. An irregular black fleck on upper part of base of the pectoral fins. Coloration preserved. Body grayish brown, with light–colored ventral surface, multiple dark spots on the dorsal fins, caudal fin and lateral surface of the body, and an irregular black spot above the base of the pectoral fin. Ventral side of abdomen light brown. Head brown, cheek light brown, a horizontal black band crossing the eyes. Urogenital papilla whitish, with sparse black pigment. Sexual dimorphism . Urogenital papilla elongates with a wide base, tapering and with a narrow tip. No distinct opening in male; clear ovipore in female ( Fig. 5 ). FIGURE 5. Urogenital papilla of Microdous hanlini sp. nov. SOU1801015–8 ( A , male) and SOU1801015–7 ( B , female). Cephalic sensory canal system. Oculoscapular canal with three preorbita (lanterior interorbital) pores A’, B and C, single interorbital pore D, single postorbital (posterior interorbital) pore E, and seven pores F to L extending posteriorly. Preopercular canal with five pores M to Q ( Fig. 6 ). Cephalic sensory papillae. Neuromasts numerous, small and densely set in mostly longitudinally arranged rows ( Fig. 6 ). Head skeleton. The skeletons of M. hanlini and M. chalmersi were investigated using X-ray microtomography ( Fig. 7 ). A pair of the frontal bones constitutes the majority of the skull roof. The frontal includes a narrow anterior supraorbital section and a widened postorbital section (or posterior section). The ratio of the width of anterior section to postorbital section is much smaller in M. hanlini than that of M. chalmersi . FIGURE 6. Patterns of main cephalic sensory pores (black spots) and papilla lines (rows of dots) of Microdous hanlini sp. nov. in lateral ( A ); ventral ( B ) and dorsal( C ) view. Preorbital pores A’, B, C; interorbital pore D; postorbital pore E; pores of posterior section of oculoscapular canal F, G, H, I, J, K, L; preopercular pores Q, P, O, N, M. FIGURE 7. Head skeleton of Microdous hanlini sp. nov. (SOU1801015–9) ( A ) and M. chalmersi (SOU1801017) ( B ) based on microCT data. COI analyses and genetic distance. The COI sequence of three paratype specimens were lodged in GenBank with accession number PP481989-PP481991, and the Sineleotris saccharae as OQ382855. The results showed that the three specimens of M. hanlini (SOU1801015–1~3) and the “ Sineleotris chalmersi ” sequence from Guangxi formed a monophyletic clade with a bootstrap value of 100 ( Fig. 8 ), suggesting that the “ Sineleotris chalmersi ” was erroneously named for M. chalmersi , but is actually a sample of M. hanlini ( Wang et al., 2019 ) . Microdous hanlini then formed a closer sister relationship to M. amblyrhynchos than to M. chalmersi ( Fig. 8 ) . FIGURE 8. Maximum-likelihood (ML) tree of Microdous hanlini sp. nov. and other species of the Odontobutidae , O. yaluensis and O. haifengensis as outgroups. The numbers by the nodes represent the bootstrap support values. The intraspecific genetic distance of M. hanlini was 0.00065~0.03361, which is much smaller than that between M. hanlini and M. chalmersi from Hainan (0.10759~0.11125) ( Table 3 ). The average genetic distance between M. hanlini and M. amblyrhynchos is 0.07283 (0.06878~0.08361) ( Table 3 ). The average genetic distance between M. hanlini and M. chalmersi is similar or greater than the genetic distance between some species of Odontobutis ( Table 4 ). Distribution. Specimens of M. hanlini examined in this study were collected from Du’an, Guangxi province ( Fig. 1 ). Other documented collection records of “ M. chalmersi ”, “ Sineleotris chalmersi ” or “ Perccottus chalmersi ” in Guangxi include nearby regions of the Liu River, the Gui River, the Zuojiang River, the Youjiang River, the Hongshui River and the Beilun River ( Gan et al., 2017 ). The detailed distribution range of M. hanlini requires further exploration. Biology. According to the measurements of all specimens obtained in this research, the maximum size of M. hanlini collected was 115.1 mm in standard length. A smaller M. hanlini was found in the stomach after dissecting one specimen of M. hanlini , suggesting that M. hanlini is carnivorous. Habitat. Microdous hanlini was collected from a rapid–flowing spring, which has rubble bottom substrate with a vegetation-covered bank. Water depth 20–40 cm ( Fig. 9 ). FIGURE 9. Habitat of Microdous hanlini sp. nov .. An unnamed stream of Du’an (23°55.94′N, 108°6.07′E), Guangxi, China. TABLE 3. Genetic distance between Microdous hanlini sp. nov. (SOU1801015–1~3, NC_045932.1), M. chalmersi (OQ319988, OQ319987), and M. amblyrhynchos (SOU1801010-1~3, GenBank number OP536373.1~ 0P536375.1).

Species	M. hanlini	M. chalmersi	M. amblyrhynchos
SOU 1801015 – 1	SOU 1801015 –2	SOU 1801015 – 3	NC _ 045932.1	OQ 319987	OQ 319988	OP 536373.1	OP 536374.1	OP 536375.1
SOU1801015–1
SOU1801015–2	0.00130
SOU1801015–3	0.00196	0.00065
NC_045932.1	0.03500	0.03355	0.03362
OQ319987	0.10927	0.10759	0.10773	0.11125
OQ319988	0.10927	0.10759	0.10773	0.11125	0.00000
OP536373.1	0.07013	0.06878	0.06878	0.08361	0.10722	0.10722
OP536374.1	0.07013	0.06878	0.06878	0.08361	0.10722	0.10722	0.00000
OP536375.1	0.07013	0.06878	0.06878	0.08361	0.10722	0.10722	0.00000	0.00000

TABLE 4. Genetic distance between six species of Odontobutis .

O. haifengensis	O. sinensis	O. interrupta	O. potamophilus	O. platycephala	O. yaluensis
O. haifengensis
O. sinensis	0.1442
O. interrupta	0.1554	0.1370
O. potamophilus	0.1527	0.1286	0.0393
O. platycephala	0.1501	0.1331	0.1288	0.1351
O. yaluensis	0.1521	0.1292	0.0747	0.0759	0.1281

Comparative material. All M. chalmersi and M. amblyrhynchos specimens examined for morphological comparison were loaned from the Fish Collection of the Shanghai Ocean University, China with the registration tags 76V8791, 76V8792, 76V9228 from Qiongzhong , Hainan , May 1976 ; HN832384 from Changjiang , Hainan , May 1983 , and 070504 from Wuzhishan , Hainan , May 1983 ; SOU1801009–1, from Wuzhishan , Hainan , August 2018 ; SOU1801010 (1~3, 7~8) from Baise City , Guangxi .