Luciogobius opisthoproctus Chen & Liao, 2024, sp. nov.
Creators: name: Chen, Kuan-Hsun
name: Liao, Te-Yu
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Perciformes
Oxudercidae
Luciogobius
Luciogobius opisthoproctus

description: Luciogobius opisthoproctus sp. nov.   
Figs 3, 4, 5 New English name: Taiwan Earthworm Goby  
Holotype.  
ASIZP 0081790, 25.8 mm SL, Taiwan, Yilan County, mouth of Daxi Creek, 24 ° 56.48 ' N, 121 ° 53.72 ' E, coll. K. H. Chen, 16 February 2023.  
Paratypes.  
17 specimens (20.6–28.1 mm SL). ASIZP 0081791, 22.9 mm SL, ASIZP 0081792, 22.9 mm SL, ASIZP 0081793, 23.8 mm SL, DOS 09993-1, 25.1 mm SL, DOS 09993-2, 24.9 mm SL, DOS 09993-3, 26.8 mm SL, DOS 09993-4, 22.8 mm SL, DOS 09993-5, 20.6 mm SL, DOS 09993-6, 22.8 mm SL, NMMB-P 39322, 22.7 mm SL, NMMB-P 39323, 21.44 mm SL, NMMB-P 39324, 21.8 mm SL, NMMB-P 39325, 23.1 mm SL, NMMB-P 39326, 27.5 mm SL, collected with holotype. ASIZP 0081794, 27.3 mm SL, DOS 09994-1, 24.3 mm SL, NMMB-P 39327, 28.1 mm SL, Taiwan, Taitung County, river mouth of Babian Creek, 23 ° 04.44 ' N, 121 ° 21.38 ' E, coll. K. H. Chen, 21 March 2023.  
Diagnosis.  
 Luciogobius opisthoproctus sp. nov. is diagnosed by the following combination of characters: total vertebrae 41–43; free pectoral-fin rays absent; second dorsal-fin rays 9–12 (usually 11); anal-fin rays 11–14 (11 or 12); pectoral-fin rays 8–12 (10 or 11); pelvic-fin length more than 50 % of pectoral-fin length; AAA distance 4.2–7.2 % (mean 5.7 %) of SL, 72.1–129.7 % (mean 99.9 %) of body depth at anus; snout length 39.7–62.7 % (mean 52.8 %) of AAA distance; pre-anus distance 80.0–92.8 % (mean 88.6 %) of pre-anal-fin length; and anterior-most pterygiophore of anal fin inserted behind the second haemal spine (Fig. 5).   
Description.  
 Morphometric measurements and meristic counts are given in Table 1. Body elongate, anteriorly cylindrical, and posteriorly compressed. Head narrowly depressed. Anterior nostril a pair of short tubes; posterior nostril round. Lower jaw slightly projecting; mouth oblique; maxilla extends posteriorly to vertical at front margin of eye. Gill opening narrow, extending from middle of pectoral-fin base to level with posterior end of jaw. Interorbital space narrower than snout length, side compressed, anteriorly swollen. A longitudinal dermal ridge present from below anterior nostril extending to behind eye. Occipital region slightly turgid (swollen) dorsally and laterally. First dorsal fin absent. Origin of second dorsal fin slightly posterior to origin of anal fin. First and second rays of second dorsal fin spinous, remaining rays soft and segmented; posterior margin of second dorsal fin rounded; second dorsal-fin rays 9–12 [9 (3), 10 (5), 11 (8) *, 12 (2)] (* for the number including holotype). Anal fin slightly posterior to anus; first and second rays of anal fin spinous, remaining rays soft and segmented; posterior margin of anal fin rounded; anal fin rays 11–14 [11 (5), 12 (7) *, 13 (4), 14 (2)]. Pectoral-fin fan-shaped and free pectoral-fin rays absent, pectoral-fin relatively small, about 5.5–8.8 % of SL; pectoral-fin rays 8–12 [8 (1), 9 (1), 10 (5) *, 11 (6), 12 (5)]. Caudal fin rounded. Pelvic fins round with frenum and complete membrane; pelvic-fin rays I, 5. Segmented caudal-fin rays 15–17 [15 (5), 16 (9), 17 (4) *]. First dorsal pterygiophore inserted between 25 th and 26 th vertebrae; last dorsal pterygiophore inserted between 31 st and 32 nd vertebrae; first anal fin pterygiophore inserted behind second haemal spine; insertion pattern not changing with numbers of fin rays; abdominal vertebrae 20–22 (usually 22), caudal vertebrae 20–22 (usually 21).   
 D 2: second dorsal-fin; A: anal-fin; P 2: pelvic-fin; P 1: pectoral-fin; C: caudal-fin; V: vertebrae; D: dorsal; hs: haemal spine; P 1 L: pectoral-fin length; BD: body depth; AN: anus; PAL: pre-anal-fin length; AAA distance: distance between anus and anal-fin origin; CPD: caudal-peduncle depth; CPL: caudal-peduncle length; PP 2 L: pre-pelvic-fin length; D 2 L: second dorsal-fin length; AL: anal-fin length; P 1 L: pectoral-fin length; P 2 L: pelvic-fin length; CL: caudal-fin length; PD 2 L: pre-second dorsal-fin length; PANL: pre-anus length; ED: eye diameter.   
Cephalic sensory system.  
 The series of cephalic sensory papillae on cheek are illustrated in Fig. 6. Row a situated behind eye, extending shortly upwards to orbital area. Row b extending from margin behind eye to upper lip. Row c starting from posterior of dermal ridge to anterior margin of eye. Single spot cp situated under row c. Row d starting from posterior margin of upper lip to anterior nostril. Row e extending from lower margin of preopercle to upper margin of lower jaw. Row i extending along weak flap on lower margin of lower jaw to lower part of preopercle. Row f in posterior of symphysial flap on chin. Row oi longitudinal, row ot and os running vertically. Row oi, os, ot separated from each other.   
Coloration.  
Body background white, dorsally yellowish, and translucent ventrally. A discontinuous row of black spots on side of body from pectoral-fin to caudal-fin base. Scattered black spots internally embedded in the abdomen and visible through the semi-transparent muscle. Scattered black spots on dorsal surface, highly dense in some individuals. Rays and membranes of dorsal-, pectoral-, pelvic-, and anal-fins transparent and yellowish at base. Caudal fin transparent, with a black, rounded blotch at base. Specimens preserved in 70 % ethanol whitish, with the same pattern of black spots when alive.  
Distribution and habitat.  
The new species is currently only known from northeastern and southeastern Taiwan. This species mainly inhabits shallow gravel creeks near coastal river mouths.  
Etymology.  
 The specific name opisthoproctus is from the Greek words opisthe (behind) and proktos (anus), in allusion to the posteriorly positioned anus (shorter AAA distance).   
Molecular analysis.  
 Thirty-nine sequences (133 bp) from 14 species were obtained and used to reconstruct an ML tree (Fig. 7), with Inu koma as the outgroup. In the topology of the ML tree, a monophyletic clade consisting of L. opisthoproctus sp. nov. was revealed. Luciogobius opisthoproctus sp. nov. and L. sp. 10 are sister species, and these two species are a sister group of a clade comprising Luciogobius spp. 8, 13, 14, 15, and 16. The genetic distances between the new species and other members of L. elongatus complex are shown in Table 2.   
Numbers in paracenteses for numbers of sequences.  
Remarks.  
 Based on the morphological approach, L. opisthoproctus sp. nov. belongs to the L. elongatus complex (Shibukawa et al. 2019) because of the following characters: absence of free pectoral-fin rays, AAA 72.1–129.7 % of body depth at anus, vertebrae 41–43, anterior pleural attaching to third abdominal vertebra, first anal-fin pterygiophore inserted behind second haemal spine, and first to second rays of dorsal- and anal-fin unbranched and spine-like. The new species is most similar to L. punctilineatus and L. sp. 11 in having yellowish coloration, a black blotch on the caudal-fin, a longitudinal line composed of scattered black spots on the sides of body, and similar _ numbers of dorsal-, anal-, pectoral-fin elements. However, L. opisthoproctus sp. nov. can be distinguished from L. punctilineatus and L. sp. 11 by the shorter AAA distance (4.2–7.2 % SL vs 11.4–16.9 % in L. punctilineatus; 9.1–10.4 % in L. sp. 11); longer pre-anus length (80.0–92.8 % of pre-anal-fin length vs 75.0–82.0 % in L. punctilineatus; 84.4–88.8 % in L. sp. 11); longer snout length (39.7–62.7 % of AAA distance vs <34.7 % in L. punctilineatus; 36.7–44.8 % in L. sp. 11); more abdominal vertebrae (20–22 vs 16–18 in L. punctilineatus; 17–18 in L. sp. 11); fewer caudal vertebrae (20–22 vs 22–24 in L. punctilineatus; 22–25 in L. sp. 11); first anal fin pterygiophore usually inserted behind the second haemal spine (vs fifth in L. punctilineatus; fourth in L. sp. 11) (Table 3). The new species can be further distinguished from L. punctilineatus in having the AAA distance less than twice the body depth at the anus (vs about twice of the body depth at anus).   
 * Indicates only one specimen is available. N / A: not available. Abbreviation: Ab V: abdominal vertebrae; Cd V: caudal vertebrae; A: anal fin; hs: haemal spine; HL: head length; SL: standard length; AAA distance: distance between anus and anal-fin origin; BD: body depth; AN: anus; SNL: snout length; PANL: pre-anus length; PAL: pre-anal-fin length; P 1 L: pectoral-fin length; P 2 L: pelvic-fin length. 1 for present study; 2 for Koreeda et al. 2022; 3 for Shibukawa et al. 2019.   
 Based on the molecular analysis, the topology showed that there is a sister-species relationship between the new species and L. sp. 10. However, L. opisthoproctus sp. nov. can be distinguished from L. sp. 10 (Table 3) in having a smaller HL (12.7–18.7 % vs 19.5–19.7 % SL), more abdominal vertebrae (20–22 vs 14) and more total vertebrae (41–43 vs 36) (Table 4). Luciogobius opisthoproctus sp. nov. can be easily distinguished from L. adapel and L. parvulus by the presence of a pelvic fin (vs absence) and further distinguished from L. adapel by the presence of a second dorsal and anal fin (vs absence); from L. elongatus, L. sp. 8, and L. sp. 9 by more dorsal-fin rays (9–12 vs usually less than 9) and anal-fin rays (11–14 vs usually less than 11), and further distinguished from L. elongatus and L. sp. 9 by presence of a well-developed frenum on the pelvic fin (vs absence). The new species can also be distinguished from Luciogobius spp. 12–16 by absence of free pectoral-fin rays (vs presence). It can be further distinguished from L. sp. 12 and L. sp. 13 by having more vertebrae in total (41–43 vs 38–39), and from Luciogobius sp. 14–16 by presence of a black blotch on the caudal-fin (vs absence) (Table 4). Luciogobius sp. 3 (sensu Maeda et al. 2008) is also similar to L. opisthoproctus sp. nov. in coloration, morphometric measurements, and meristic counts. However, due to the limited information from only one juvenile provided by Maeda et al., further study is needed to verify the relationship of these sepcies. Species within the L. elongatus species complex, as defined by Shibukawa et al. (2019), exhibit a unique combination of characters that differentiate them from species in other complexes. However, the presence of a single free pectoral-fin ray of L. parvulus and L. spp. 12–16 of the L. elongatus complex is not constant. This trait is apparently not a reliable character to distinguish L. elongatus complex from L. guttatus complex (vs presence of a free pectoral-fin ray).   
 Abbreviation: D 2: second dorsal-fin; A: anal-fin; P 1: pectoral-fin; P 2: pelvic-fin; Ab V: abdominal vertebrae; Cd V: caudal vertebrae; V: vertebrae; ND: not developed; W-D: well-developed. * = sometimes absent. 1 for Okiyama, 2001; 2 for present study; 3 for Shibukawa et al. 2019; 4 for Koreeda and Motomura 2021; 5 for Maeda et al. 2008.   
 Luciogobius opisthoproctus sp. nov. sometimes co-occurs with L. grandis Arai, 1970 and L. guttatus Gill, 1859 near the mouths of streams. However, L. opisthoproctus sp. nov. can be morphologically distinguished by its yellowish body color, differing from the bronze color in L. grandis and the brown color in L. guttatus (Fig. 8). Additionally, it can also be readily distinguished from other two species by several distinctive features, such as a transparent caudal fin with one black blotch on its base (vs opaque), a pair of fan-shaped pectoral-fin (vs triangular in L. grandis and round in L. guttatus), absence of pigmentation on pectoral-, anal-, and second dorsal fins (vs presence), and unbranched first to second rays of dorsal- and anal-fins (vs only first ray unbranched).   
Comparative material.  
 L. elongatus: one specimen, OMNH - P 14170, 37.1 mm SL, Nagasaki Coast, Fuke, Misaki, Sennan, Osaka, Japan, coll. Kanai, M., 27 May 2001. L. grandis: ten specimens, DOS 09990, 30.5–54.1 mm SL, Hualien River, Hualien County, Taiwan, coll. K. H. Chen, 31 January 2022. L. guttatus: ten specimens, DOS 09988, 38.4–58.7 mm SL, Jinhuken, Yilan County, Taiwan, coll. K. H. Chen, 10 August 2021.
description: Published as part of Chen, Kuan-Hsun & Liao, Te-Yu, 2024, A new species of the genus Luciogobius Gill, 1859 (Teleostei, Oxudercidae) from Taiwan, pp. 241-254 in ZooKeys 1206 on pages 241-254, DOI: 10.3897/zookeys.1206.118757