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Research Article
Limnichthys koreanus, a new species of creediid fish (Teleostei, Acropomatiformes, Creediidae) from Korea
expand article infoYu-Jin Lee‡, Jin-Koo Kim‡
‡ Pukyong National University, Busan, Republic of Korea

Corresponding author: Jin-Koo Kim ( taengko@hanmail.net )

Academic editor: Yahui Zhao
© 2024 Yu-Jin Lee, Jin-Koo Kim.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation: Lee Y-J, Kim J-K (2024) Limnichthys koreanus, a new species of creediid fish (Teleostei, Acropomatiformes, Creediidae) from Korea. ZooKeys 1214: 59-75. https://doi.org/10.3897/zookeys.1214.128977
ZooBank: urn:lsid:zoobank.org:pub:E6F05128-E591-43D9-B0D1-2232513FF668
Open Access

Abstract

Limnichthys koreanus sp. nov. is described on the basis of the holotype and 11 paratypes from subtidal waters of Seogwipo, Jeju Island, Korea. The new species had previously been regarded as the Northern Hemisphere population of the anti-equatorial L. fasciatus, but molecular analyses of mitochondrial COI and 16S genes recovers deep genetic divergences of 9.4% and 15.0% between the new species and topotypical specimens of L. fasciatus. Limnichthys koreanus sp. nov. is distinguished from all other species of Limnichthys based on the following combination of colouration and morphological characteristics: 38-40 vertebrae; 0–6 dorsal saddles joining mid-lateral stripe; small infraorbital sensory pores; a single median interorbital pore; and well-developed vomerine teeth. Summary characters for comparative congeneric species are provided.

Key words

benthic species, Jeju Island, sand burrower, taxonomy

Introduction

The family Creediidae consists of 18 species accommodated in eight globally distributed genera, most of which are concentrated in subtropical and tropical coastal waters of the Indo-Pacific Ocean (Nelson et al. 2016; GBIF Secretariat 2023; Fricke et al. 2024). Known colloquially as sand burrowers or sand lancers, creediids are small, slender, sand-dwelling fishes that camouflage and hide in the uppermost layer of sand in wait of passing prey before rapidly darting out and back into the sand in a boomerang fashion (Nelson 1985; Cozzi and Clark 1995). The creediid fishes have the following characteristics: less than 5–6 cm in length; prominent eyes positioned dorsally on the head; fleshy snout; no spines in the dorsal or anal fin rays (Nelson 1985). Studies on Limnichthys have compared their morphological phylogenetics and examined skeletal structures, new species, including feeding behavior, and early life history (Nelson 1978, 1979, 1985; Leis 1982; Shimada and Yoshino 1987; Pettigrew and Collin 1995; Yoshino et al. 1999; Pettigrew et al. 2000; Shibukawa 2010; Fricke and Golani 2012). The creediid genus Limnichthys is of particular taxonomic interest, with nearly all its species adopting anti-equatorial distribution. The possibility of the existence of cryptic populations has been discussed for a long time (Nelson 1978).

Although creediid species occur far from each other they are highly morphologically similar. Six species of Limnichthys are currently recognized as valid: L. fasciatus Waite, 1904; L. marisrubri Fricke & Golani, 2012; L. nitidus Smith, 1958; L. orientalis Yoshino, Kon & Odabe, 1999; L. polyactis Nelson, 1978; and L. rendahli Parrott, 1958. With the exception of L. nitidus, which occurs from tropical to temperate water of the Indo-Pacific Ocean, the other species of Limnichthys exhibit anti-equatorial distributions (Nelson 1985; GBIF Secretariat 2023). Notably, L. fasciatus exhibits a disjunct, anti-equatorial distribution in both hemispheres, but its status as a single, widespread species has not been properly investigated (Nelson, 1978). Morphological and molecular comparisons of specimens identified as L. fasciatus from Korea in the Northern Hemisphere indicate that they are different from topotypical examples of L. fasciatus from southeastern Australia. Accordingly, we describe L. koreanus sp. nov. on the basis of 12 specimens collected during a monitoring survey of subtropical fish species from the subtidal zone of Jeju Island, Korea. The new species is compared with congeneric species, and summary accounts and phylogenetic relationships for species of Limnichthys are discussed.

Materials and methods

Meristics, morphometrics, and specimen deposition

Methods for counting measuring follow Waite (1904), Nelson (1978), and Yoshino et al. (1999). Measurements were recorded to the nearest 0.1 mm using vernier calipers. Morphometric values are summarized in Tables 1, 2, expressed as percentages of the standard length (SL) and head length (HL). Images of specimens were taken using a digital camera (D750; Nikon, Japan). Detailed morphological characteristics were examined with a stereomicroscope (SZX-16; Olympus, Tokyo, Japan).

Table 1.
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Voucher number, institution, collected date, and GenBank number of specimens used in present study.

Species Voucher Number n Institution Collected location (country) Date GenBank number
COI 16S rRNA
Limnichthys koreanus MABIK PI00060703 (PKU 63120) 1 National Marine Biodiversity Institute of Korea Moseulpo, Jeju Island (South Korea) 2022.08.15 OR541978 OR543335
MABIK PI00060704 (PKU 63121) 1 2022.08.15 OR541979 OR543336
MABIK PI00060705 (PKU 63122) 1 2022.08.15 OR541980 OR543337
PKU 21427 1 Pukyong National University 2022.07.13 OR541981 OR543338
PKU 21528 1 2022.08.15 OR541982 OR543339
PKU 21529 1 2022.08.15 OR541983 –
PKU 21530 1 2022.08.15 – OR543340
PKU 22426 1 2023.07.17 – –
PKU 22427 1 2023.07.17 – –
PKU 22428 1 2023.07.17 – –
PKU 22626 1 Seongsanpo, Jeju Island (South Korea) 2023.12.16 PP708995 PP708997
PKU 22627 1 2023.12.16 PP708996 PP708998
L. fasciatus I.44122-031 1 Australian Museum Central Coast, NSW (Australia) 2007.05.08 OR544519 –
I.44627-025 1 Nelson Bay, NSW (Australia) 2008.04.08 OR544515 OR543322
TCWC 17569.03 1 Texas A&M University Central Coast, NSW (Australia) 2015.02.22 OR544522 OR543331
CAS 109236* 3 California Academy of Science Lord Howe Island, NSW (Australia) 1902.12.03 –1903.01.21 – –
CAS 38242 3 Lord Howe Island, NSW (Australia) 1973.02.09 – –
CAS 120473 7 Sydney, NSW (Australia) 1998.04.15
CAS 219288 1 Viti Levu (Fiji) 2002.02.10
NSMT-P-125200 1 National Museum of Nature and Science Japan – LC753137 OR543330
NSMT-P-125201 1 Japan – LC753135 OR543329
NSMT-P-125202 1 Japan – OR546102 OR543328
L. cf. nitidus CAS 228250 5 California Academy of Science Hawaii Island (USA) 1993.04.15 – –
KAUM-I 124455 Kagoshima University Amami Islands (Japan) 2018.12.16 OR544523 OR543332
KAUM-I 143956 Amami Islands (Japan) 2020.07.03 OR544524 OR543333
L. orientalis KPM-NI 51923 Kanagawa Prefectural Museum of Natural History - (Japan) 2010.07.20 LC753149** –
Trichonotus setiger – – – KU944772** NC034345**
T. marleyi – – JF494737** –

* Paratypes specimens. ** Sequences were obtained from GenBank.

Osteological details were determined from X-ray images, cleared and stained specimens, and micro-CT data. Micro-CT scans were taken using Phoenix V-Tome-X C450 Volume Graphics® VGSTUDIO Max software and handled using Volume Graphics® myVGL viewer. We performed osteological staining with a paratype specimen (PKU 22428) using a modified version of the method detailed in Song and Parenti (1995). Vertebral counts were presented as a total number of abdominal to caudal vertebrae, which was followed by Nelson (1978). Terminology of skeletal bones followed by Lucena Rosa (1995).

Twelve specimens of the new species (35.8–45.3 mm TL, 33.4–40.0 mm SL) were collected from subtidal zones at depths of 1–5 m in Seogwipo, Jeju Island, Korea between July 2022 and December 2023 (Fig. 1). Specimens were vouchered in Pukyong National University (PKU) and National Marine Biodiversity Institute of Korea (MABIK) with register numbers (PKU 21427; PKU 21528–21530; PKU 22426–22428; PKU 22626–22627; PKU 63120–63122, MABIK PI00060703– MABIK PI00060705). Tissue samples were taken from the right side of the body, preserved in 99% ethanol, and deposited in the PKU. We followed the immersion specimen production manual of the MABIK, under the National Institute of Marine Biological Resources of the Ministry of Oceans and Fisheries. One specimen was anatomized to investigate the gonadal development. Comparative specimens were loaned and investigated from various museums and institutions, including the Australian Museum, Sydney (AMS), the Kagoshima University Museum, Korimoto (KAUM), the Kanagawa Prefectural Museum of Natural History, Odawara (KPM), Fish Section and Center for Molecular Biodiversity Research, National Museum of Nature and Science, Tokyo (NSMT), the California Academy of Sciences, San Francisco (CAS), and the Biodiversity Research and Teaching Collections, Department of Wildlife and Fisheries Sciences, Fisheries Sciences, Texas A&M University (TCWC). Institutional codes follow Sabaj (2023).

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.

Comparative materials of L. cf. nitidus used in this study were collected from Pacific Ocean (Japan, and Hawaii, USA), which is far from the type locality of the species (Mozambique, South Africa). Given that creediid fishes, in particularly those belonging to the genus Limnichthys, exhibit local endemism with the possibility of undescribed cryptic diversity, we refer to these non-topotypical comparative specimens as L. cf. nitidus. X-ray images and micro-CT images of syntypes and non-type material of L. fasciatus were examined, as well as skeletal sketch by Nelson (1978). See list of material examined below.

DNA extraction, amplification, and sequencing

Genomic DNA was extracted using tissues the AccuPrep Genomic DNA Extraction Kit (Bioneer, Daejeon, Republic of Korea). Mitochondrial cytochrome c oxidase subunit I (COI) and 16S ribosomal RNA (16S) were amplified from extracted gDNA using the polymerase chain reaction. Primer sets for 16S and COI follow by Palumbi (1996) and Ward et al. (2005) respectively. Polymerase chain reaction with a mixture (2 μL 10× buffer, 1.5 μL dNTPs, 2 μL primer set, 0.1 μL Taq polymerase, and 2 μL genomic DNA (gDNA) made up to 20 μL with distilled water) was performed under the following conditions: initial denaturation step at 95 °C for 5 min followed by 35 cycles of denaturation at 95 °C for 30 s, annealing at 52–54 °C for 45 s, and extension at 72 °C for 45 s, with a final extension at 72 °C for 7 min. Amplification was conducted using a thermal cycler (MJ mini PCT-1148; Bio-Rad, Hercules, CA, USA). Sequences were read by BigDye Terminator v. 3.1 cycle sequencing kits (Applied Biosystems, Foster City, CA, USA) with an ABI PRISM 3730XL analyzer (96 capillary type; Applied Biosystems).

Molecular analysis

A total number of 5,750 bp in 16S and 7,564 bp in COI sequences were obtained. To analyze the relationships among sequences, alignment was performed using ClustalW (Thompson et al. 1994) in BioEdit 7 (Hall 1999). The final sequence lengths used in the analysis were 401 bp in 16S, and 417 bp in COI per individual. Genetic distances were calculated using Mega 11 (Tamura et al. 2021) with the Kimura 2-parameter (K2P) model (Kimura 1980). Neighbour-joining trees were constructed based on 1,000 bootstrap replications by maximum composite likelihood model using Mega 11 software (Tamura et al. 2004). Sequence data for other species in the genus Limnichthys (Limnichthys orientalis) and outgroup of two species [Trichonotidae: Trichonotus marleyi (JF494737 in COI); T. setiger (NC034345 in 16S; KU944772 in COI)] were obtained from the NCBI database. The accession numbers of all sequences are provided in Table 1.

Results

Taxonomy

Acropomatiformes Gill, 1893 (new Korean name: Ban-dit-bul-ge-reu-chi-mok)

Creediidae Waite, 1899 (new Korean name: Byeol-ba-ra-gi-gwa)

Limnichthys Waite, 1904 (new Korean name: Byeol-ba-ra-gi-sok) (Tables 2, 3, Figs 2–7)

Limnichthys koreanus sp. nov.

https://zoobank.org/462BD9BA-4E7A-44AC-96EB-52F8F972771D
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 PI00060703 (PKU 63120).

Paratypes. South Korea • 44.5 mm TL, 38.4 mm SL; 15 August 2022; same data as holotype; MABIK PI00060704 (PKU 63121); South Korea • 45.3 mm TL, 40.0 mm SL; 15 August 2022; same data as holotype; MABIK PI00060705 (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. 3A, Table 2).

Figure 2. 

Limnichthys koreanus sp. nov. A holotype, MABIK PI00060703 (PKU 63120), 37.3 mm SL, Moseulpo B paratype, MABIK PI00060704 (PKU 63121), 38.4 mm SL, Moseulpo C paratype, MABIK PI00060705 (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 PI00060703 (PKU 63120), 37.3 mm SL, South Korea B Limnichthys fasciatus, syntype, AMS I.5858, 43 mm SL, preserved in Australian Museum.

Table 2.
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Comparison of counts in Limnichthys spp. Parentheses indicate counts of the holotype specimen.

L. koreanus sp. nov. L. fasciatus (Australia & Fiji) L. fasciatus (Japan) L. cf. nitidus (Japan & Hawaii Is.) L. marisrubri (Red Sea) L. orientalis (Japan) L. polyactis (New Zealand) L. rendahli (New Zealand)
References In this study In this study In this study In this study Nelson 1978 Fricke and Golani 2012 In this study Yoshino et al. 1999 Nelson 1978 Fricke and Golani 2012
Number of specimens 12 19 3 24 22 8 34 –
Counts
Dorsal fin rays 25–27 (25) 24–27 26–27 22–25 22–24 21–23 28–32 29–33
Anal fin rays 26–28 (28) 26–29 27–28 26–28 24–26 24–25 31–34 30–32
Pectoral fin rays 12–13 (12) 11–14 12–13 11–12 13–15 10–11 12–13 13–16
Segment caudal fin rays 8–9 (8) 8 8 8 8 8 8 8
Lateral line scales 42–46 (43) 38–43 43–44 36–38 37–41 41–43 41–46 –
Teeth on vomer Well-developed Developed Developed Developed – Developed Developed –
Median interorbital pore 1 2 1 1 – 1 1 –
Total vertebrae 38–40 (40) 40–45 39–41 39–41 – 40–41 43–45 43–45
Number of epural 2 2 2 1 – 1 1 2
Midlateral stripe Present Present Present Present or absent Present Absent Present Present
Dorsal saddles (number) 5–9 (8) 7–9 7–9 8–12 11–14 6–11 7–9 6–8
Dorsal saddles joining midlateral stripe (number) 0–6 (4) 5–9 5–6 – – – 3–5 3–6

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. 4A); palatine teeth absent; pharyngeal teeth present; tongue slender and pointed. A single of median interorbital sensory pore (Fig. 5A); infraorbital sensory pores very smaller than posterior nostril (Fig. 5E); 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); 6–7th pectoral fin rays longest. Pelvic fin ahead of pectoral fin; 3rd pelvic fin ray longest; pelvic fin not elongated; pelvic fin with I, 5; anterior process of pelvic girdle well separated (Fig. 6A) pelvic girdle with upper projecting process (Fig. 7A). Dorsal fin rays 25–27 (25); Origin of dorsal fin at 3–4th 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. 6B). Lateral line scales 42–46; lateral line scales trilobed (Fig. 8A); lateral line from opercular to precaudal gradually running down. Body covered with cycloid scales (Fig. 8B); 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.

Table 3.
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Proportional measurements in Limnichthys koreanus sp. nov.

Holotype (MABIK PI00060703) Paratypes (n = 11)
Standard length (mm) 37.3 33.42–40.0
Morphometric characters
In SL (%)
Body depth 13.3 10.7–12.8
Head length 26.1 24.5–32.3
Head depth 7.1 7.6–10.6
Snout length 3.8 4.0–5.7
Orbital diameter 3.8 2.6–4.1
Interorbital length 2.1 1.8–2.6
Postorbital length 17.0 15.4–20.2
Upper jaw length 9.7 6.7–11.3
Predorsal length 46.6 44.2–50.5
Prepectoral length 26.8 23.8–30.0
Prepelvic length 23.2 22.3–26.0
Preanal length 41.4 41.9–45.9
Dorsal fin base length 44.0 41.4–49.5
Anal fin base length 52.0 52.9–60.8
In HL (%)
Snout length 16.9 15.2–17.7
Orbital diameter 15.8 9.2–16.7
Interorbital length 4.7 4.4–6.7
Upper jaw length 34.1 24.6–37.7

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).

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 PI00060703, 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.

Genetic comparisons

COI (510–614 bp) and 16S 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 16S 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%.

Figure 9. 

Neighbour-joining tree was constructed based on mtDNA 16S 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.

Discussion

We discovered a new species, Limnichthys koreanus sp. nov., through morphological and molecular analysis of 12 specimens collected from the subtidal zone (at 1–2 m in depth) of Jeju Island, Korea between August 2022 and December 2023. Limnichthys species are remarkable because their morphological characteristics are strikingly similar despite high endemism. They commonly have dorsal saddle patterns, and the cirri on the lower jaw are well developed. Initially, this new species was considered a cryptic species of L. fasciatus because it appeared to have no morphological differences; it only exhibited a large genetic distance. However, we found significant morphological traits differing from type specimens as follows: the new species has fewer vertebrae; the infraorbital sensory pores below the middle of the eyes smaller than the posterior sensory pores; separation of the anterior process of both pelvic girdles; the highly developed vomerine teeth. Compared with the other species, the new species has spots (rarely absent) on the dorsal fin rays, in contrast to the transparent dorsal fin rays of L. fasciatus. The number of dorsal saddle patterns in the new species ranges from 5 to 9, whereas it ranges from 7 to 9 in L. fasciatus. Notably, differences in caudal fin ray segments were first discovered in this study. Limnichthys species typically have eight caudal fin ray segments and slightly developed vomerine teeth (Nelson 1985; Fricke and Golani 2012). However, our species has 8–9 branched caudal fin rays and well-developed vomerine teeth. Additionally, a previously unreported upper process of pelvic girdle was observed in the new species compared with previous skeletal sketches (Figs 6, 7).

In terms of genetic results, we considered that the individuals used for molecular analysis of L. fasciatus were far from the type locality (Lord Howe Island), located 600 km east of Australia. We representatively used three specimens from Nelson Bay and the central coast of New South Wales, the collected location of specimens are about 7–800 km away from each other. We first confirmed that morphological characters of them were perfectly matched with type locality specimens (13 paratypes and 6 specimens from Lord Howe Island), and they have no genetic differences among the three specimens. Therefore, we treated them as truly L. fasciatus, which showed deep divergence from our species. Interestingly, we found cryptic diversity in the northwestern Pacific Ocean. Limnichthys fasciatus from Japan has similar morphological characteristics to L. koreanus sp. nov., but these species have significant genetic divergences. They are well separated from Australian specimens, so they have possibility as a new species. Limnichthys species can be distinguished by their distribution, except for L. nitidus, and they might have high cryptic diversity and endemism (Fig. 1). Limnichthys nitidus is known for having cryptic complex like L. fasciatus. According to the original description and subsequent study, the L. nitidus complex was treated as subspecies, Indian Ocean species (L. nitidus nitidus) and West Pacific Ocean species (L. nitidus donalsi) by ichthyologists (Nelson 1978; Lucena Rosa 1995; Yoshino et al. 1999; Randall 2005). Fricke and Golani (2012) separated each species as L. nitidus (Indian Ocean species) and L. donalsi (Pacific species), but it is still unclear. For this reason, in this study, we referred to the species as L. cf. nitidus, indicating that it is likely L. nitidus but with some uncertainty in the exact identification. Based on ecological traits of Limnichthys, such as hiding in the sand and limited mobility, there is a possibility that each region can show high endemism. In the future study, we need molecular comparisons to clarify the genetic populations.

We also noted remarkably prominent color variation among individuals. Specimens of L. koreanus sp. nov. collected from western Jeju Island (Moseulpo) were more similar to L. fasciatus compared with specimens collected from eastern Jeju Island (Seongsanpo). Nevertheless, mtDNA analysis did not reveal infraspecies sequence variation. We hypothesize that the observed variation in body color of L. koreanus sp. nov. is influenced by differences in habitat substrates (bright in the west vs dark in the east), as suggested by Armbruster and Page (1996), who reported that benthic fish with dorsal saddle patterns can vary based on substrate characteristics such as color or particle size. In our study, Limnichthys koreanus sp. nov. was confirmed only in the west (Moseulpo) and east (Seongsanpo) areas of Jeju Island. Future research should investigate its habitat preferences relating to the size of sand (or gravel) for understanding their distribution pattern. All specimens of L. koreanus are adults; individuals collected from June to August exhibit maturity for spawning. They are mostly in maturation–mature stages, with an average egg diameter of 0.62–0.65 mm. Creediid fish lay pelagic eggs (Regan 1916; Leis 1982). Specimens were also collected from very shallow coastal waters at depths of 1–5 m. Therefore, spawning may occur near the collection site, highlighting the need for future studies of their spawning and reproductive habitats.

Key to species of four species of the genus Limnichthys from the West Pacific Ocean

1 Dorsal fin rays 25 or more; a single epural bone; dorsal saddles joining midlateral stripe absent 2
– Dorsal fin rays 25 or fewer; two epural bones; dorsal saddles joining midlateral stripe present 3
2 Pectoral fin rays 11–12; anal fin rays 26–28; lateral line scales 36–38 L. cf. nitidus
– Pectoral fin rays 10–11; anal fin rays 24–25; lateral line scales 41–43 L. orientalis
3 A single interorbital pore; total vertebrae 38–40; dorsal saddles joining midlateral stripe (s) 0–6; vomerine teeth well developed L. koreanus sp. nov.
– A pair of interorbital pores; total vertebrae 40–45; dorsal saddles joining midlateral stripes 5–9; vomerine teeth slightly developed L. fasciatus

Comparative specimens

Limnichthys fasciatus: AMS I.5854; AMS I.5855; AMS I.5856; AMS I.5858, syntypes, 13 specimens, 29–43 mm SL, Lord Howe Island, NSW, Australia; AMS I.44627, 28.7 mm SL, Baronda Headland, south side, NSW, Australia; TCWC 17569, 41.1 mm TL, Forester Beach, Tasman Sea, NSW, Australia.

Limnichthys cf. nitidus: CAS 228250, 5 specimens, 18.44–20.73 mm SL, Hawaii Island, USA; KAUM-I 124455, 21.1 mm TL, 2018.12.16, 31°25'33.0"N, 130°07'11.4"E, south of Kome-jima island, Kataura, Kasasa, Minami-satsuma, Kagoshima, Japan, hand net, collected by Harutaka Hata; KAUM-I 143956, 1 specimen, 21.9 mm TL 2020.06.03, 27°52'03.6"N, 128°58'03.6"E, Daisuke Uyeno, Kagoshima, Japan, Hand net, collected by Ryuichi Nakagawa.

Acknowledgements

We sincerely thank Dr Kerryn Parkinson and Dr Amanda Hay of the Australian Museum, Dr Heather L. Prestridge of Texas A&M University, Dr Hiroyuki Motomura of Kagoshima University, Prof. Yoshiaki Kai of Kyoto University, Dr Masanori Nakae of the National Museum of Nature and Science, and Dr Catania of the California Academy of Sciences. We also thank the anonymous reviewers for their valuable comments that improved the quality of this article.

Additional information

Conflict of interest

The authors have declared that no competing interests exist.

Ethical statement

No ethical statement was reported.

Funding

This work was supported by the management of Marine Fishery Bio-resources Center (2024) funded by the National Marine Biodiversity Institute of Korea (MABIK).

Author contributions

Yu-Jin Lee wrote the text and made the figures. Jin-Koo Kim edited and approved the manuscript for publication.

Author ORCIDs

Yu-Jin Lee https://orcid.org/0000-0002-9511-0610

Jin-Koo Kim https://orcid.org/0000-0002-8499-406X

Data availability

The data underpinning the analysis reported in this paper are deposited at GBIF, the Global Biodiversity Information Facility, and are available at https://doi.org/10.15468/a436d4.

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