Limnichthys koreanus, Lee & Kim, 2024

Lee, Yu-Jin & Kim, Jin-Koo, 2024, Limnichthys koreanus, a new species of creediid fish (Teleostei, Acropomatiformes, Creediidae) from Korea, ZooKeys 1214, pp. 59-75 : 59-75

Limnichthys koreanus sp. nov.

Table 1 , 2 , Figs 2 , 3 , 4 , 5 , 6 , 7 New English name: Korean sand burrower; new Korean name: Tti-byeol-ba-ra-gi

Material examined.

Holotype: South Korea • 45.95 mm TL, 39.5 mm SL; tidal pool on Jeju Island ; 33 ° 13 ' 21.1 " N, 126 ° 14 ' 30.9 " E; 1 m; 15 August 2022; collector Yu-Jin Lee & Jin-Koo Kim; scoop net; MABIK PI 00060703 ( PKU 63120 ).

Paratypes. South Korea • 44.5 mm TL, 38.4 mm SL; 15 August 2022; same data as holotype; MABIK PI 00060704 ( PKU 63121 ) ; South Korea • 45.3 mm TL, 40.0 mm SL; 15 August 2022; same data as holotype; MABIK PI 00060705 ( PKU 63122 ) ; South Korea • 1 ♀, 44.5 mm TL, 37.3 mm SL; 14 July 2022; same data as holotype; PKU 21427 ; South Korea • 38.5 mm TL, 34.5 mm SL; 15 August 2022; same data as holotype; PKU 21528 ; South Korea • 38.3 mm TL, 33.6 mm SL; 15 August 2022; same data as holotype; PKU 21529 ; South Korea • 35.8 mm TL, 33.4 mm SL; 15 August 2022; same data as holotype; PKU 21530 ; South Korea • 42.4 mm TL, 38.5 mm SL; 17 July 2023; same data as holotype; PKU 22426 ; South Korea • 43.2 mm TL, 37.6 mm SL; 17 July 2023; same data as holotype; PKU 22427 ; South Korea • 44.1 mm TL, 39.4 mm SL; 17 July 2023; same data as holotype; staining specimen; PKU 22428 ; South Korea • 37.5 mm TL, 33.8 mm SL; tidal pool on Jeju Island ; 33 ° 27 ' 37.0 " N, 126 ° 56 ' 02.1 " E; 5 m; 15 December 2023; hand net; PKU 22626 ; South Korea • 38.4 mm TL, 35.7 mm SL; tidal pool on Jeju Island ; 33 ° 27 ' 37.0 " N, 126 ° 56 ' 02.1 " E; 5 m; 15 December 2023; collector Yu-Jin Lee & Jin-Koo Kim; hand net, depth PKU 22627 .

Diagnosis.

Combined number of dorsal and anal fin rays 52–55; vertebrae 38–40; lateral line scales 42–46; a single median interorbital pore; vomerine teeth well developed; pelvic girdle separated each other; dorsal saddle patterns 5–9; dorsal saddles joining mid-lateral stripe 0–6 (Fig. 3 A , Table 2 ).

Description.

Counts and measurements of type materials are shown in Table 1 ; holotype values indicate in parenthesis in table and description. Body elongated; cylindrical and posteriorly compressed. Head to body slope almost flat; head length 24.5–32 % in SL (26.1 %); head depth 7–10.6 % (7.1 %); snout length 3.8–5.7 % (3.8 %) in SL (Table 3 ). Eyes on dorsal of head, large, and bulging. Snout terminal; upper jaw projects more than lower jaw; upper and lower jaws with a single row of minute conical teeth; a pair of filament-like antennas on anterior upper jaw (or absent); cirri on lower jaw; lips fleshy; vomer with well-developed conical teeth (Fig. 4 A ); palatine teeth absent; pharyngeal teeth present; tongue slender and pointed. A single of median interorbital sensory pore (Fig. 5 A ); infraorbital sensory pores very smaller than posterior nostril (Fig. 5 E ); anterior nostril tubular. Branchiostegal rays 7. Opercular flap covered pectoral fin base. Pectoral fin not reaching anal fin origin; pectoral fin rays 12–13 (12); 6–7 th pectoral fin rays longest. Pelvic fin ahead of pectoral fin; 3 rd pelvic fin ray longest; pelvic fin not elongated; pelvic fin with I, 5; anterior process of pelvic girdle well separated (Fig. 6 A ) pelvic girdle with upper projecting process (Fig. 7 A ). Dorsal fin rays 25–27 (25); Origin of dorsal fin at 3–4 th anal fin ray; posterior of dorsal and anal fin reaching precaudal (free from caudal). Anus ahead half of body. Anal fin rays 26–28 (28); anal fin length uniform. Caudal peduncle length very short. All fin rays not branched (only caudal fin branched). Segment of caudal fin rays 8–9 (8). Two epurals (Fig. 6 B ). Lateral line scales 42–46; lateral line scales trilobed (Fig. 8 A ); lateral line from opercular to precaudal gradually running down. Body covered with cycloid scales (Fig. 8 B ); no scales on frontal; scales on cheeks well developed. Gill rakers of first gill arch with small and low multi-spined stubs like patch; gill rakers 2 + 10.

Coloration when fresh.

Body whitish pink. Dorsal and ventral edges pale orange, brown, or white. Dark stripe below eyes. Eyeballs dark brown or black. Opercular pinkish and slightly transparent. Dorsal saddle patterns 5–9, dark brown, dark orange, or black. Distinct horizontal bar on body. Number of dorsal saddle patterns joining with lateral bar 0–6. Pelvic, pectoral, and anal fins transparent. Darkish spots on dorsal fin rays. Caudal fin rays similar in color to body pattern.

Coloration when preserved.

Body white. Head white with black or dark brown spots. Dark stripe below eyes. Lateral band black or dark brown. All fins transparent. Spots on dorsal and caudal fin rays. Dorsal or lateral patterns not clearly visible after fixation, depending on preservative solution.

Distribution.

The species is presently known only from Jeju Island, Korea.

Biology and habitat.

They inhabit relatively thick sand substrates (or maybe more like fine gravels), often hiding almost entirely in the sand in subtidal zone. They tended to dart out to catch prey (e. g. copepods) and then return to their original position. Females have mature eggs in their gonads from June to August. The eggs (522 per individual) are approximately 0.62–0.65 mm in diameter. In contrast, a specimen from December lacked developed gonads.

Etymology.

The epithet of the new species, koreanus , refers to the type locality ( Korea) where the species were collected.

Morphological comparisons.

Limnichthys koreanus sp. nov. is clearly distinguished from the other species in the genus Limnichthys in having significantly developed vomerine teeth and number of total vertebrae (38–40) (Table 3 ; Fig. 4 ). The new species is most similar to Limnichthys fasciatus , but can be separated based on the following characters: well-developed vomerine teeth (significant bugling vs weak bugling in L. fasciatus ); total vertebrae count (38–40 vs 40–45 in L. fasciatus ); presence of spot pattern on dorsal- and caudal-fin rays (absent in L. fasciatus ); size of the infraorbital sensory pore below the middle of the eyes (smaller than the posterior nostril [PN] vs similar or larger than the PN in L. fasciatus ); a single of median interorbital pore (two in L. fasciatus ) (Fig. 5 ); separation of the anterior process of pelvic girdle (nearby in L. fasciatus ) (Fig. 6 ). Especially, L. fasciatus including paratype specimens in the south hemisphere has well-separated interorbital median pores (having two pores in L. fasciatus from Lord Howe Island, Fiji, and Sydney). Due to the proximity between the two interorbital median pores, they are often misidentified as one pore. Limnichthys koreanus further differs from L. cf. nitidus , L. orientalis , and L. polyactis in having: two instead of one epural; dorsal-fin rays (25–27 vs 22–25 in L. cf. nitidus ; 21–23 in L. orientalis ; 28–32 in L. polyactis ); anal-fin rays (26–28 vs 26–28 in L. cf. nitidus ; 24–25 in L. orientalis ; 31–34 in L. polyactis ), segement caudal-fin rays (8–9 vs 8); and presence of midlateral body stripe. L. polyactis is the endemic species which only distributed in New Zealand, and it is geographically separated from the other species (Fig. 1 ). Limnichthys marisrubri and L. rendahli , which have a single epural, are distinguished following characters: dorsal fin rays (25–27 vs 24–27 in L. fasciatus vs 22–24 in L. marisrubri vs 29–33 in L. rendahli ), anal fin rays (26–28 vs 26–29 in L. fasciatus vs 24–26 in L. marisrubri vs 30–32 in L. rendahli ).

Genetic comparisons.

COI (510–614 bp) and 16 S rRNA (442–508 bp) sequences were obtained from L. koreanus sp. nov. After alignment with National Center for Biotechnology Information (NCBI) sequences of other Limnichthys species (Fig. 9 ), we found significant genetic divergences of 9.4 % and 15.0 % for L. fasciatus in the COI and 16 S rNA genes from near the type locality (southeastern Australia), respectively. Furthermore, genetic distances of 16.2 % and 18.4 % were observed for L. cf. nitidus . Only COI gene sequences were obtained for L. orientalis , indicating a genetic distance of 20.9 %.

Figures

Figure 1. Map showing sampling sites and distribution of Limnichthys spp. Each color marks indicate each species: Red marks and arrow showing collected location of Limnichthys koreanus sp. nov.; pink marks showing L. fasciatus, which is anti-equatorial species, and yellow star mark showing the type locality of L. fasciatus; blue marks showing Limnichthys marisrubri in the Red Sea; purple marks showing L. nitidus in Indo-Pacific Ocean; orange marks showing L. orientalis in Japan; yellow marks showing L. polyactis in New Zealand; green marks showing L. rendahli in New Zealand.

Figure 2. Limnichthys koreanus sp. nov. A holotype, MABIK PI 00060703 (PKU 63120), 37.3 mm SL, Moseulpo B paratype, MABIK PI 00060704 (PKU 63121), 38.4 mm SL, Moseulpo C paratype, MABIK PI 00060705 (PKU 63122), 40.0 mm SL, Moseulpo D paratype, PKU 21528, 34.5 mm SL, Moseulpo E paratype, PKU 21529, 33.6 mm SL, Moseulpo F paratype, PKU 21530, 33.4 mm SL, Moseulpo G paratype, PKU 22626, 33.8 mm SL, Seongsanpo H paratype, PKU 22627, 35.7 mm SL, Seongsanpo. Scale bars indicate 10 mm. Left images showing lateral views; right images showing dorsal views. Voucher numbers are annotated in the bottom right corner of each image. Scale bars: 10 mm.

Figure 3. Radiographs of Limnichthys species using CT-scan A Limnichthys koreanus sp. nov., holotype, MABIK PI 00060703 (PKU 63120), 37.3 mm SL, South Korea B Limnichthys fasciatus, syntype, AMS I. 5858, 43 mm SL, preserved in Australian Museum.

Figure 4. Vomerine teeth of Limnichthys spp. The red arrows indicate vomerine teeth. A, B Limnichthys koreanus sp. nov.; well-developed vomerine teeth; broad and bugling; conical teeth C, D L. fasciatus, weak-developed vomerine teeth; minute conical teeth E, F L. cf. nitidus; developed vomerine teeth; narrow and bugling; conical teeth G, H L. orientalis; slightly developed vomerine teeth; conical teeth.

Figure 5. Dorsal and lateral view of head of Limnichthys spp. The photos show sensory canals and pores on head A, E L. koreanus sp. nov., sensory canals weak-developed, infraorbital sensory pores small; some species have antennas on snout B, F L. fasciatus; AMS I. 44627; Nelson Bay, NSW; 28.7 mm SL; sensory canals well-developed; infraorbital sensory pores large C L. cf. nitidus; CAS 228250; Hawaii Island, USA; 20.24 mm SL; sensory canals well-developed D L. orientalis; KPM - NI 51923; Japan; 29.4 mm SL; sensory canals well developed. Abbreviations: AN, anterior nostril; ANP, anterior nasal pore; IMO, interorbital median pore; IO, infraorbital pores; LC, lachrymal pore; PN, posterior nostril; PNP, posterior nasal pore; ST, supratemporal pores.

Figure 6. Separation of the anterior process of pelvic girdle A Limnichthys koreanus sp. nov., holotype, MABIK PI 00060703, 39.5 mm SL, South Korea, pelvic girdle well-separated from each other B Limnichthys fasciatus, syntype, AMS I. 5858, 43 mm SL, preserved in Australian Museum, pelvic girdle close to each other.

Figure 7. Photos showing detailed morphological traits in a staining specimen of Limnichthys koreanus sp. nov. A upper process of pelvic girdle B two epurals. Arrows indicate terms of parts.

Figure 8. Two types of scales of Limnichthys koreanus sp. nov. A pored lateral line scales with trilobed shape B a scale on the body. Scales are cycloid.

Figure 9. Neighbour-joining tree was constructed based on mtDNA 16 S rRNA and COI gene. The tree showing genetic distances among Limnichthys species. Bootstrap values based on 1000 replicates were showed 100 %, the values are omitted. The red box indicates Limnichthys koreanus sp. nov.; blue box indicates L. fasciatus from Southeastern Australia; green boxe indicates L. cf. nitidus from Japan; yellow box indicates L. orientalis from Japan; Trichonotidae species was used as outgroup.