A New Cryptic Species of Splitfin Fish from Taiwan with Revision of the Genus Synagrops (Acropomatiformes: Synagropidae)

© 2024 Academia Sinica, Taiwan Open Access A New Cryptic Species of Splitfin Fish from Taiwan with Revision of the Genus Synagrops (Acropomatiformes: Synagropidae) Dominique P. Mediodia1,2,3 , Chia-Hao Chang4, Hsuan-Ching Ho5,6 , Tomáš Přikryl7, and Chien-Hsiang Lin1,* 1Biodiversity Research Center, Academia Sinica, Nankang 115, Taipei, Taiwan. *Correspondence: E-mail: [email protected] (Lin) E-mail: [email protected] (Mediodia) 2National Taiwan Normal University, Taipei 106, Taiwan 3Institute of Marine Fisheries and Oceanology, College of Fisheries and Ocean Sciences, University of the Philippines Visayas, Philippines 4Department of Science Education, National Taipei University of Education, Taipei 10671, Taiwan. E-mail: [email protected] (Chang) 5Department and Graduate Institute of Aquaculture, National Kaohsiung University of Science and Technology, Kaohsiung 807618, Taiwan. E-mail: [email protected] (Ho) 6Graduate Institute of Marine Biology, National Dong Hwa University, Hualien 974301, Taiwan 7Institute of Geology of the Czech Academy of Sciences, Department of Paleobiology and Paleoecology, Czech Republic. E-mail: [email protected] (Přikryl) Received 1 September 2023 / Accepted 14 March 2024 / Published 9 July 2024 Communicated by Hin-Kiu Mok A new species of splitfin fish, Synagrops atrumoris sp. nov., from Dongsha Island, Taiwan, South China Sea, is described based on its morphological characteristics, including osteology and otolith morphology, and DNA sequence. Synagrops atrumoris sp. nov. is closely similar to Synagrops japonicus and can be distinguished by its black mouth cavity covering the lower portion of the tongue, posteriorly enlarged and complex basioccipital fossae, and a triangular otolith with a strong postero-dorsal angle, as well as a strong genetic difference. In addition, the taxonomy of the genus Synagrops was revised. Available published data, together with our results, suggest that S. bellus is a synonym of S. japonicus. Key words: Taxonomy, Ichthyology, Biodiversity, Otolith, Phylogenetic analyses BACKGROUND The fish order Acropomatiformes, commonly known as lanternbellies, have oblong and moderately compressed bodies covered by ctenoid or cycloid scales with notable ventral light-emitting organs in some members (Okamoto 2014). They are primarily found in the deeper-shelf, upper slope, and seamounts of tropical and subtropical areas of the world (SmithVaniz et al. 1999; Okamoto and Gon 2018; Santos et al. 2019). There are 20 families and over 300 species under the order Acropomatiformes sensu Smith et al. (2022). One of the families is Synagropidae Smith, 1961, previously classified within the family Acropomatidae, which previously included seven genera: Acropoma, Apogonops, Doederleinia, Malakichthys, Neoscombrops, Synagrops, and Verilus. In more recent reports by Ghedotti et al. (2018) and Smith et al. (2022), the genus Synagrops was classified under the family Synagropidae. The genus Synagrops can be distinguished from other genera based on its non-serrated pelvic-fin spines, separated two dorsal fins with IX + I, 9 elements, anal fin with II spines, no vacant interneural gap under D1, naked head with a robust cranial crest forming a W shape, pre-dorsal formula 0/0/0+2, basioccipital fossae extending to the ventral part of the exoccipital, posteriorly opening the myodome, no denticles at the preopercle but with 1–3 strong ridges, small rows of teeth on the ectopterygoid, subrectangular shaped otolith, and 25 total vertebrae (Schwarzhans and Citation: Mediodia DP, Chang CH, Ho HC, Přikryl T, Lin CH. 2024. A new cryptic species of splitfin fish from Taiwan with revision of the genus Synagrops (Acropomatiformes: Synagropidae). Zool Stud 63:20. doi:10.6620/ZS.2024.63-20. Zoological Studies 63:20 (2024) doi:10.6620/ZS.2024.63-20 1 © 2024 Academia Sinica, Taiwan Prokofiev 2017). To date, there are only two species recognized under the genus Synagrops: Synagrops japonicus (Döderlein, 1883) and Synagrops bellus (Goode and Bean, 1896) (Schwarzhans and Prokofiev 2017). Synagrops japonicus and S. bellus are geographically isolated and are currently considered two separate species. However, it is necessary to mention that Heemstra et al. (2022) synonymized S. bellus with S. japonicus without providing any rational evidence. Synagrops japonicus is only found in the Indo-West Pacific, while S. bellus is distributed in the Atlantic (Heemstra 2016; Schwarzhans and Prokofiev 2017). However, studies have reported potential range expansion through the transport of juveniles from ballast waters (Orsi-relini 2009; Serena et al. 2022), wherein S. japonicus was also reported in the Mediterranean Sea (Hannachi et al. 2015; Serena et al. 2022) and S. bellus in New Caledonia, Western Pacific (Fricke et al. 2011). Until now, the Japanese splitfin S. japonicus has been reported around Taiwan (Wang and Lee 2019; Xu et al. 2019; Shao 2023). However, a putative new cryptic species under Synagrops has been identified based on its morphological characters (including osteological characters and otoliths) and COI sequences. The purpose of the present work is to describe the new species and revise the genus Synagrops. MATERIALS AND METHODS Sampling and specimen preparation Fresh specimens were collected from commercial trawl fishing around Dongsha (Pratas) Island, Taiwan (coordinates 18°56' to 20°40'N and 112°57 to 116°49'E) from 2022 to 2023 (Fig. 1). Researchers were not present during the actual fishing but instead acquired the samples from the landing sites. Thirty specimens of S. atrumoris sp. nov. (> 100 mm SL) were analyzed and compared with 30 specimens of S. japonicus (Table 1; Tables S1–S2). Museum specimens of S. japonicus from the Biodiversity Research Museum, Academia Sinica, Taipei, Taiwan (ASIZP; n = 20) and the National Museum of Marine Biology and Aquarium, Pingtung, Taiwan (NMMB-P; n = 121), and S. bellus collected from the Atlantic Ocean and deposited in the Museum of Comparative Zoology, Harvard University, Cambridge, Fig. 1. Sampling sites of S. atrumoris sp. nov. and the distribution of S. japonicus in Taiwan based on actual data and published reports (Shao 2023). page 2 of 16Zoological Studies 63:20 (2024) © 2024 Academia Sinica, Taiwan Massachusetts, United States (MCZ; n = 49), were also examined (Tables S1–S2). Length (mm) was measured using a digital caliper and weighed (g) using a digital scale. All specimens were then photographed and preserved in 75% ethyl alcohol. Muscle tissue from the right side of the caudal region was collected and preserved in 95% ethyl alcohol and stored at -20°C for DNA extraction. Sagittal otoliths (n = 63) and dry skeletons (n = 9) were prepared for otolith and osteological analyses. The holotype and paratypes of S. atrumoris sp. nov. are deposited at ASIZP under the registration code ASIZP0081726–ASIZP0081733, and NMMBP under the registration code NMMBP39198, NMMBP39199, and NMMBP39120 (Table S3). Morphological and meristic analyses Methods for taking morphometric and meristic data followed Hubbs and Lagler (1958), with modifications on the measurements of body depth and the 1st dorsal fin height. The following morphometric characters for S. atrumoris sp. nov. were measured: Standard length (SL), measured from tip of snout to posterior end of hypural plate; head length (HL), Table 1. Morphometric and meristic data of Synagrops atrumoris sp. nov., Synagrops japonicus (Döderlein, 1883), and Synagrops bellus (Goode and Bean, 1896) Synagrops atrumoris sp. nov. Synagrops japonicus Holotype Paratypes This study (fresh collections) Museum collections Museum collections of S. bellus No. of specimens 29 ASIZP0081726–0081733 30 (Table S2) 5 from NMMBA and 5 from ASIZP (Table S2) 15 from MCZA (Table S2) SL (mm) 173.6 112.7–206.9 64.3–202.5 73.4–220.0 99.7–191.7 %SL Range (mean) Range (mean) Range (mean) Range (mean) HL 35.1 33.0–37.7 (35.4) 33.4–39.4 (36.2) 25.7–40.2 (35.2) 32.9–38.5 (35.3) PDL 36.9 34.0–40.7 (37.7) 34.3–42.6 (39.0) 36.4–43.3 (40.2) 35.8–40.1 (37.8) PAL 67.2 64.2–74.9 (68.6) 65.6–79.2 (68.3) 62.8–71.9 (68.8) 66.0–72.6 (69.5) PPL 35.9 33.3–37.2 (35.5) 29.4–38.6 (35.6) 32.5–40.3 (36.0) 32.9–38.0 (35.3) PVL 37.4 33.8–40.5 (36.8) 31.9–43.0 (34.2) 30.9–40.6 (35.3) 34.2–40.6 (36.7) BD 25.2 22.4–28.1 (24.5) 22.5–28.3 (24.7) 22.6–26.2 (24.5) 23.5–26.0 (25.3) ED 10.3 9.2–11.5 (10.4) 9.1–12.0 (10.6) 8.3–11.3 (10.6) 9.4–11.8 (10.7) SN 10.1 8.0–12.8 (9.6) 7.7–11.5 (9.7) 8.0–10.7 (9.5) 7.9–9.9 (8.9) IW 9.1 8.2–10.2 (9.3) 4.1–10.5 (8.9) 8.1–9.9 (8.9) 8.6–9.9 (9.3) UJL 14.4 13.0–15.8 (14.4) 12.6–15.7 (14.5) 13.3–16.1 (14.5) 13.7–14.9 (15.5) LJL 14.5 13.9–17.1 (15.3) 14.0–16.9 (15.6) 14.6–17.1 (15.6) 15.5–17.6 (16.4) SOH 4.1 2.7–6.5 (3.8) 2.4–8.0 (3.9) 1.3–3.5 (3.9) 1.5–2.7 (2.3) POL 16.2 15.3–20.1 (16.5) 9.8–19.6 (17.0) 9.2–33.5 (19.9) 12.8–17.4 (15.6) DS1 20.3 15.0–22.1 (19.3) 16.6–23.7 (19.7) 14.9–21.3 (19.7) 12.7–21.0 (18.3) DS2 14.8 11.9–17.3 (15.0) 12.0–18.4 (15.4) 12.6–17.5 (15.4) 10.4–19.4 (16.6) PFL 22.1 16.8–26.3 (22.4) 18.0–26.9 (23.1) 15.3–25.1 (23.1) 20.5–23.2 (25.6) VSL 13.6 10.6–14.6 (12.8) 10.9–15.7 (13.0) 9.3–14.0 (13.0) 8.7–15.9 (12.2) VFL 18.4 15.7–22.8 (19.4) 13.6–22.6 (19.4) 16.2–23.0 (19.4) 19.1–24.3 (21.9) AS1 2.2 1.6–3.8 (2.3) 1.5–3.4 (2.2) 1.8–2.8 (2.2) 1.4–2.6 (2.0) AS2 6.8 5.7–8.5 (6.7) 5.5–7.9 (6.7) 5.7–7.6 (6.6) 6.1–7.7 (7.1) AFL 15.2 11.0–17.1 (15.2) 12.2–17.9 (14.7) 10.5–17.2 (14.5) 12.0–17.6 (15.2) CFL 21.7 22.0–29.3 (26.3) 24.7–30.9 (27.0) 23.0–27.6 (24.9) 22.5–29.1 (25.1) FL 12.4 10.2–20.0 (12.7) 10.1–16.2 (13.4) 12.4–18.1 (14.4) 10.7–14.8 (18.1) CPL 24.2 22.6–28.9 (25.2) 22.4–29.5 (25.0) 19.5–30.3 (24.2) 18.6–24.8 (22.1) CPD 9.8 9.2–11.1 (10.2) 9.7–11.5 (10.6) 9.5–11.9 (10.3) 8.9–10.1 (10.7) Dorsal fin elements IX, I, 9 IX, I, 9 IX, I, 9 IX, I, 9 IX, I, 9 Anal fin elements II, 7 II, 7 II, 7 II, 7 II, 7 Pectoral fin elements 15 15–16 15–16 15–16 14–16 Pelvic fin spines I, 5 I, 5 I, 5 I, 5 I, 5 Caudal fin elements 9 + 8 8–9 + 8–10 8–9 + 8–10 8–9 + 8–10 8–10 + 8–10 Gill rakers 2 + 10 2–3 + 9–10 2–3 + 9–10 3 + 9–10 2–4 +10–13 Lateral Scale 31 29–32 29–33 29–32 28–31 page 3 of 16Zoological Studies 63:20 (2024) © 2024 Academia Sinica, Taiwan measured from tip of snout to posterior margin of the gill cover; predorsal length (PDL), measured from tip of snout to origin of dorsal fin; preanal length (PAL), measured from tip of snout to origin of anal fin; prepectoral length (PPL), measured from tip of snout to upper base of pectoral fin; pre-ventral fin length (PVL), measured from tip of snout to origin of pelvic fin; body depth (BD), measured from the pelvic fin base to the adjacent dorsal point; eye diameter (ED), measured from the anterior to posterior portion of the eye; snout length (SN), measured from tip of snout to anterior margin of the eye; interorbital width (IW) measured as the narrowest distance of eye; upper jaw length (UJL), measured from tip of snout to posterior end of maxilla; lower jaw length (LJL), measured from tip of the lower jaw to articulate; suborbital height/depth (SOH), measured from the lower margin of eye to gill cover; postorbital length (POL), measured from the posterior margin of the eye to gill cover; 1st dorsal fin height (DS1), length of 3rd dorsal spine; 2nd dorsal fin height (DS3), length of the longest dorsal fin ray; pectoral fin length (PFL), length of the longest pectoral fin ray; pelvic spine length (VSL), length of the pelvic spine; pelvic fin length (VFL), length of the longest pelvic fin ray; 1st anal spine length (AS1), length of the 1st anal spine; 2nd anal spine length (AS2), length of the 2nd anal spine; anal fin length (AFL), length of the longest anal ray; caudal fin length (CFL), measured from middle of hypural to end of the upper lobe; fork length (FL), length of the shortest ray of the caudal fin; caudal peduncle length (CPL), measured from the posterior end of the anal fin base to middle of the hypural; caudal peduncle depth (CPD), narrowest area of the caudal peduncle. Meristic data such as dorsal fin elements, dorsal spine and fin ray; anal fin elements, anal spine and fin ray; pelvic fin elements, pelvic spine and fin ray; pectoral fin elements, pectoral rays; caudal fin elements, unsegmented unbranched soft ray, segmented unbranched soft ray, segmented branch soft rays and spines of the upper lobe and lower lobe; gill rakers, developed rakers on the outer surface of the 1st gill arch on the upper and lower limbs; and lateral line scales, scales at the lateral line of the left side including the small scales on caudal-fin base, were examined on the left side of the specimens unless damaged. Radiographic images were taken at the National Museum of Marine Biology and Aquarium, Pingtung, Taiwan (NMMBA) to count the vertebrae (the ural centrum with attached hypural complex was counted as one vertebra). Phylogenetic analyses Thirty samples of S. atrumoris sp. nov. and 10 S. japonicus were used for the phylogenetic analyses. DNA extraction was done using DNA extraction Kit S (Cat No./ID: GS100, Geneaid). PCR amplification of partial mitochondrial COI gene (650 bp) was then performed by adding 5 ng template DNA, 12.5 μL of 2x Taq PCR MasterMix (GN-PCR201-01, Genomix), and 12.5 μmol each of the forward and reverse primers; FishF1+2 (5'-TCR ACY AAY CAY AAA GAY ATY GGC AC-3'); reverse: FishR1 (5'-TAG ACT TCT GGG TGG CCA AAG AAT CA-3') or FishR2 (5'- ACT TCA GGG TGA CCG AAG AAT CAG AA-3') into the mixture until it reaches 25 μL final volume using distilled water (Chang et al. 2016). The thermal cycling procedure was done in one cycle at 95°C for 4 min, then 35 cycles of denaturation at 95°C for 30 s, at 45–55°C for 30 s, followed by 72°C for 30 s and, finally, at 72°C for 7 min. A DNA Fragment Extraction Kit (Geneaid, Taipei, Taiwan) was used to purify the PCR products, which were submitted to Mission Biotech Inc., Taipei, Taiwan, together with the forward primer for sequencing. Quality score-based training of sequence ends to Q20 was manually performed using FinchTV. COI sequences were submitted to GenBank. Additional sequences from GenBank were downloaded to develop the tree (Table 2). Parascombrops spinosus (Acropomatiformes: Synagropidae), Parascombrops philippinensis (Acropomatiformes: Synagropidae), and Bathyclupea hoskynii (Acropomatiformes: Bathyclupeidae) were used as outgroups in the analysis (Smith et al. 2022). COI sequences were then aligned in MACSE v2 software based on the corresponding amino acid translation of protein-coding nucleotide sequences (Ranwez et al. 2018). A Neighbor-Joining (NJ) analysis based on Kimura 2-parameter (K2P) distance metric was done to build a distance tree with 10,000 bootstrap replicates in MEGA 11.0.10 (Tamura et al. 2021). RESULTS SYSTEMATICS Order Acropomatiformes Gill, 1893 Family Synagropidae Smith, 1961 Genus Synagrops Günther, 1887 Synagrops atrumoris sp. nov. Mediodia & Lin (Figs. 2–9) urn:lsid:zoobank.org:act:EB93B24D-AC2A-48EB-ACDC568526CA7218 English name: Dongsha Blackmouth splitfin; Chinese name: 東沙黑口尖牙鱸. Holotype: ASIZP0081729 (173.6 mm SL) collected in Dongsha Island, Taiwan, South China Sea page 4 of 16Zoological Studies 63:20 (2024) © 2024 Academia Sinica, Taiwan Table 2. The haplotypes of the COI gene of the genus Synagrops from freshly collected samples and NCBI sequences and three species used as outgroups in the study Source Scientific name Sampling Locality NBCI accession number Specimen accession number Haplotype code This study S. atrumoris sp. nov. Dongsha Island, Taiwan, South China Sea OR918329 OR918330 OR918337 OR918338 OR918343 OR918347 OR918350 OR918351 M44 M43 M35 M34 M25 M21 M18 M17 AH_1 Dongsha Island, Taiwan, South China Sea OR918331 OR918348 M42 M20 AH_2 Dongsha Island, Taiwan, South China Sea OR918332 M40 AH_3 Dongsha Island, Taiwan, South China Sea OR918333 OR918344 OR918354 M39 M24 M12 AJH_4 Dongsha Island, Taiwan, South China Sea OR918334 M38 AH_5 Dongsha Island, Taiwan, South China Sea OR918335 M37 AH_6 Dongsha Island, Taiwan, South China Sea OR918336 M36 AH_7 Dongsha Island, Taiwan, South China Sea OR918339 M33 AH_8 Dongsha Island, Taiwan, South China Sea OR918341 M27 AH_9 Dongsha Island, Taiwan, South China Sea OR918342 M26 AH_10 Dongsha Island, Taiwan, South China Sea OR918345 M23 AH_11 Dongsha Island, Taiwan, South China Sea OR918346 M22 AH_12 Dongsha Island, Taiwan, South China Sea OR918349 M19 AH_13 Dongsha Island, Taiwan, South China Sea OR918352 M16 AH_14 Dongsha Island, Taiwan, South China Sea OR918353 M15 AJH_15 Dongsha Island, Taiwan, South China Sea OR918355 M11 AH_16 Dongsha Island, Taiwan, South China Sea OR918356 M7 AH_17 Dongsha Island, Taiwan, South China Sea OR918357 M4 AH_18 Dongsha Island, Taiwan, South China Sea OR918358 M3 AH_19 GenBank S. japonicus Western Australia JN313205 AJH_15 Western Australia JN313203 AJH_4 Western Australia JN313204 JH _27 This study S. japonicus Dongsha Island, Taiwan, South China Sea OR922331 OR922334 SJ020 SJ017 JH_20 Dongsha Island, Taiwan, South China Sea OR922325 SJ026 JH_21 Dongsha Island, Taiwan, South China Sea OR922326 OR922329 SJ025 SJ022 JH_22 Dongsha Island, Taiwan, South China Sea OR922327 SJ024 JH_23 Dongsha Island, Taiwan, South China Sea OR922328 OR922333 SJ023 SJ018 JH_24 Dongsha Island, Taiwan, South China Sea OR922330 SJ021 JH_25 Dongsha Island, Taiwan, South China Sea OR922332 SJ019 JH_26 GenBank S. japonicus South China Sea KP266764 JH_26 Taiwan KU943433 JH _28 Taiwan KU943432 JH _29 Taiwan KU943431 JH _30 Taiwan KU892833 JH _31 Japan JF952871 JH _32 Japan JF952870 JH_33 Japan JF494629 JH_34 Japan JF494625 JH_35 GenBank S. bellus Mexico MF041138 BH_36 Mexico MF041302 BH_37 Mexico MF041378 BH_38 Mexico MF041464 BH_39 United States of America MG856877 BH_40 Mexico KR086919 BH_41 United States of America KT883640 BH_42 Mexico HM389721 BH_43 United States of America MG856390 Parascombrops spinosus United States of America MH378633 OH_44 Parascombrops philippinensis Philippines ON398606 OH_45 Bathyclupea hoskynii India KP244494 OH_46 page 5 of 16Zoological Studies 63:20 (2024) © 2024 Academia Sinica, Taiwan (coordinates 18°56'N, 112°57'E). Paratypes: Twenty-nine specimens with 124.6–179.6 mm SL collected from near the holotype locality: ASIZP0081726 (5 specimens, 155.7–178.7), ASIZP0081726 (6 specimens, 154.2–171.1), ASIZP0081728 (10 specimens, 136.3–179.6), ASIZP0081730 (8 specimens, 124.6–170.4), and ASIZP0081731 (1 specimen, 137.8). Diagnosis: A species of Synagrops differs from its congeners with the following combinations of characters: black mouth cavity covering the lower portion of the tongue in larger individuals (> 100 mm SL), basioccipital fossae are posteriorly enlarged and complex, triangular otolith with a pointed anterior rim and vertical posterior rim. Description: Morphometric and meristic values are provided in table 1. Data presented are for the holotype and range of paratypes in parenthesis. Body elongated, less compressed laterally. Head massive and naked with a prominent W-shaped cranial crest. Mouth terminal and large. Eyes large with small black pigments circulating the margin. Snout short. Anus near the pelvic fin base. Dorsal, pelvic, and anal fins with prominent dark spots at the tip. The 1st and 2nd dorsal fins are separated. First dorsal spine in the 1st dorsal fin shortest, 3rd fin longest. The third fin ray in the 2nd dorsal fin longest. First dorsal-fin rays IX; 2nd dorsal fin rays I, 9 (I, 8–9). Anal fin near the posterior part of the body. First anal spine shorter than 2nd anal spine. Third anal fin ray longest. The pterygiophore of the proximal-middle radial 1st anal fin broad and bent towards the 1st haemal spine. Anal-fin rays II, 7. Pectoral fin not reaching anus. Pectoral-fin rays i15–15i (i15–16i). Non-serrated pelvic spine. Pelvic-fin rays I, 5. Caudal fin forked. Principal caudal-fin rays 9 + 8 (8–9 + 8–9), complete caudal fin formula including procurrent rays is 8, i, 9+8, i, 8. Small rows (2–5) of denticles on the ectopterygoid. The lateral side of the lower jaw with 2 (2–3, n = 8) strong canines and 4 (4–5, n = 8) small canines protruding in the upper jaw. Small serrations in preopercle with 2–3 rounded small ridges at the lower rear margin. Swimbladder reaching cranium. Gills with 2 (2–3) short rakers at the upper arch and 10 (8–10) long at the lower arch; rakers dark brown to black; gill filaments reddish pink. Predorsal formula 0/0/0+2/. Vertebrae count 25 (10 abdominal and 15 caudal). Scales cycloid and easily shed. Lateral scales 30 (29–32). Coloration: Body color black-to-gray with a metallic sheen in the entire body, pale-cream color without scales. Metallic color in the ventral part of the body. Osteological notes: Skeletal characters of the new species were studied in all skeleton parts. It generally resembles that of S. japonicus. The only significant differences were identified in the otic region of the skull and the immediately adjacent portion of the vertebral column. Due to that reason, only the neurocranium (especially its otic portion) and the anterior-most part of the vertebral column are emphasized in the study. The neurocranium in the dorsal view is almost squarish in shape, somehow broader posteriorly. The skull roof is ornamented by a system of anteriorly diverging ridges and large openings, creating a prominent W-shaped cranial crest. The dorsal part of the otic section is extensively covered by epaxial musculature. The dorsal margin of the neurocranium in lateral view is convex, while the ventral margin is more or less straight (the only exception is the ventrally prominent vomerine section). The neurocranium in the lateral view is significantly lower and shorter in the ethmoid region than in the otic region. The orbit is large, approximately 40% of the length of the neurocranium. The supraoccipital crest is short but relatively deep. The openings of the myodome are enlarged dorsally, and the prootic participate in the construction of the myodome margins just by small and short sections in the anterolateral corners. The basioccipital fossae are emarginated by the exoccipital laterally (the ventral margin of this skeletal element is swollen), the prootic anterolaterally, and the basioccipital anteriorly and medially. The medial section of the basioccipital protrudes at the caudal part to the lateral spurs and is in contact with the medial side of the exoccipital. The posterior part of the basioccipital fossae is shifted posteriorly, and its margin is defined by ventro-laterally bony outgrowths of the 1st vertebra. The whole complex of the basioccipital fossae in S. atrumoris sp. nov. is antero-posteriorly segmented, and the complete construction extends to the 1st vertebra. Otolith: The otolith is triangular with a pointed anterior rim and a vertical posterior rim. The dorsal and ventral rims are oblique anteriorly, interrupted by distinctive angles forming the highest part of the otolith. Beyond these angles, both rims exhibit a relatively horizontal and flat profile towards the pronounced angle. Notably, there is a pronounced angle situated at both the postero-dorsal and postero-ventral corners. However, the postero-ventral angle appears more prominent and may extend further towards the posterior. The otoliths are thin. The outer face is concave, and the inner face is convex. The dorsal margin is irregular with small crenulations, specifically on the anterodorsal margin. The horizontal part of the ventral margin and the posterior margin are crenate. The sulcus is deep and well-differentiated into the ostium and cauda. A funnel-like ostium is widely open antero-dorsally. There is a large oblong ostial colliculum situated below the longitudinal midline of the ostium. The cauda is page 6 of 16Zoological Studies 63:20 (2024) © 2024 Academia Sinica, Taiwan deepened slightly, directing upward before curving strongly (about 90°) at the most posterior region, with its tip directing antero-ventrally. It is narrowing towards the neck. Cristae are well-developed. A notch is present and the antirostrum is small. Etymology: The specific name is a combination of the Latin “atrum”, meaning black, and “oris”, meaning mouth, in relation to its diagnostic black mouth floor. Distribution: Currently known from the Dongsha Islands, Taiwan, and the South China Sea. Possibly from the south of Scott Reefs, Western Australia (see below). Size: The largest sample examined in this study is 206.88 mm SL. Phylogenetic analyses: Out of 68 COI sequences used in this study from 3 taxa, we have detected 46 haplotypes and 506 aligned base pairs, which contained 169 variable sites and 102 parsimony informative sites. The NJ tree revealed there are two groups (Group 1 and Group 2) with high supports (bootstrapping value > 90) (Fig. 9), and the average pairwise genetic distance (K2P) between these two groups is 0.06. Group 1 includes S. bellus and nearly all S. japonicus specimens, but the two species nest each other within the group. The average K2P distance within the group is 0.01. Group 2 contains all specimens belong to S. atrumoris sp. nov. and three sequences of S. japonicus (74–128 mm SL) from south of Scott Reefs, Western Australia (JN313203– JN313205), and the average K2P distance within the group is 0.01. DISCUSSION Cryptic nature of the new species The poorly studied species of the genus Synagrops, S. atrumoris, has been recognized within the large collection of S. japonicus specimens from the landings of the trawling fishery. The new species can be unquestionably placed within the genus Synagrops based on the non-serrated pelvic fin spine, 2 anal fin spines, naked top of the head, and small rows of teeth on the ectopterygoid (Schwarzhans and Prokofiev 2017). Although most of the morphological characters are similar in both species (Tables 1–2; Fig. 3), S. atrumoris can be differentiated from S. japonicus by a number of characters, of which the most easily recognizable is the coloration of the mouth cavity (Fig. 4). Based on the 121 specimens of S. japonicus in the NMMBA-P, we found five specimens with black mouths, in addition to the two specimens out of 20 examined from ASIZP. However, it is necessary to validate this classification by checking the basioccipital fossa and the otolith, which can further verify the distinction between the two species. Synagrops atrumoris has an entirely black mouth covering the lower portion of the tongue in larger individuals (> 100 mm SL), while in S. japonicus the roof of the mouth is black, especially in large specimens, but the lower portion of the tongue is light-colored (Fig. 4). However, there are S. japonicus that individuals have black mouths but with grayish coloration on the tongue with patches of white spots. The mouth coloration is difficult to distinguish in smaller-sized specimens. In both species, the otic part of the skull shows differences in the morphology and construction of posterior openings for myodome and basioccipital fossa (Fig. 5). The posterior openings for the myodome are symmetrically located at the anteroventral surface of the otic section. In S. atrumoris, the openings are enlarged dorsally, and the prootic participate in the construction of their margins just by small and short sections in the antero-lateral corners (Fig. 5). The same structure in S. japonicus is shifted to a more ventral position (and thus seems larger in the ventral view), and the prootic emarginated significantly larger portion of its anterior, lateral, and posterior edges (Fig. 5). There is also similarity in the construction of the myodome and basioccipital fossae between S. japonicus and S. bellus which are visible in radiographs (Fig. 6). Another distinguishable difference between these two species is in the construction of the basioccipital fossae (Figs. 6–7). These openings are bilaterally symmetrical, located just in front of the basioccipital and 1st vertebra articulation and housing anteriorly enlarged and bifurcated swim bladder horns (Schwarzhans and Prokofiev 2017). In S. atrumoris, the basioccipital fossa is emarginated by the exoccipital laterally (the ventral margin of this skeletal element is swollen), the prootic antero-laterally, and the basioccipital anteriorly and medially (Fig. 7). The medial section of the basioccipital gives distal rise to lateral spurs in contact with the medial side of the exoccipital. The posterior part of the basioccipital fossa is shifted posteriorly, and its margin is defined by ventro-lateral bone, which outgrows on the 1st vertebra. The whole complex of the basioccipital fossae in S. atrumoris is antero-posteriorly segmented and construction is completed by the 1st vertebra. Contrary to this state, the basioccipital fossae of S. japonicus are simple, large, and widely opened posteroventrally, their posterior part is not enlarged, and the 1st vertebra is not incorporated into the construction of this structure. Furthermore, the basioccipital lacks the lateral spurs (Fig. 7). The individual bony elements supporting this structure show significant differences in proportions. page 7 of 16Zoological Studies 63:20 (2024) © 2024 Academia Sinica, Taiwan Moreover, the otolith shape of S. atrumoris is triangular with a pointed anterior rim and a vertical posterior rim (Fig. 8), while S. japonicus has a pentagonal shape with a tapered anterior end (Rivaton and Bourret 1999; Smale et al. 1995; Lin and Chang 2012; Nolf 2013). Both otoliths have a concave outer face and convex inner face, but that of S. atrumoris is moderately thicker than that of S. japonicus, particularly in the anterior portion (Fig. 8E1–2 vs G1–2). Serena et al. (2022) documented a right otolith of S. japonicus, which they mistakenly identified as a left otolith in their publication. This particular otolith exhibits similarities to that of S. atrumoris, but the specimen was broken on the anterior portion, and the figure provided in the publication was not properly oriented, resulting in a distortion of the specimen’s appearance. The two monophyletic groups with high support in NJ phylogenetic tree and a notable genetic distance between them demonstrate that S. atrumoris (Group 2) is a distinct species from S. japonicus and S. bellus (Group 1) (Fig. 9). S. japonicus and S. bellus form a monophyletic group with a low average within-group K2P genetic distance, suggesting that S. japonicus and S. bellus are actually a single species. Given that the Fig. 3. Synagrops atrumoris sp. nov., A–D, paratypes, fresh, A, ASIZP0081728, 159.0 mm SL; B, ASIZP0081728, 130.3 mm SL; C, ASIZP0081728, 176.8 mm SL; D, ASIZP0081728, 137.6 mm SL. Synagrops japonicus (Döderlein, 1883), E–F, non-types, fresh, E, ASIZP0081733, 168.6 mm SL; F, ASIZP0081733, 156.5 mm SL. Synagrops bellus (Goode and Bean, 1896) G–H, non-types, preserved, G, MCZ49930 172 mm SL; H, MCZ49930 213 mm SL. Scale bar = 10 mm. Fig. 2. Synagrops atrumoris sp. nov. A, ASIZP0081729, holotype, 173.60 mm SL, fresh and B, radiograph. Scale bar = 10 mm. page 8 of 16Zoological Studies 63:20 (2024) © 2024 Academia Sinica, Taiwan Fig. 5. Neurocrania of A–B, Synagrops atrumoris sp. nov., non-type, CHLP2000314, 178.9 mm SL, and C–D, Synagrops japonicus (Döderlein, 1883), non-type, CHLP2000309, 184.1 mm SL showing ventral (A and C), and lateral views (B and D) emphasizing the prootic, exoccipital, basioccipital, 1st vertebra, and 2nd vertebra. The actual images are presented in figure S1. Scale bar = 10 mm. Fig. 4. Mouth color of Synagrops atrumoris sp. nov., paratype, ASIZP0081731, 165.5 mm SL, Synagrops japonicus (Döderlein, 1883), non-type, ASIZP0081731, 152.8 mm SL, and Synagrops bellus (Goode and Bean, 1896), non-type, MCZ49930, 172.98 mm SL. A, fresh and B, preserved in alcohol. Not to scale. page 9 of 16Zoological Studies 63:20 (2024) © 2024 Academia Sinica, Taiwan Van der Laan R, Fricke R, Eschmeyer WN. 2023. Eschmeyer’s catalog of fishes: classification. Available at: http://www.calacademy. org/scientists/catalog-of-fishes-classification/. Accessed 15 Nov. 2023. Xu L, Van Damme K, Hong L, Ji Y, Wang X, Du F. 2019. A molecular approach to the identification of marine fish of the Dongsha Islands (South China Sea). Fish Res 213:105–112. doi:10.1016/ j.fishres.2019.01.011. Supplementary materials Fig. S1. Neurocrania of A–B, Synagrops atrumoris sp. nov., non-type, CHLP2000314, 178.9 mm SL, and C– D, Synagrops japonicus (Döderlein, 1883), non-type, CHLP2000309, 184.1 mm SL showing ventral (A and C), and lateral (B and D) views emphasizing the prootic, exoccipital, basioccipital, 1st vertebra, and 2nd vertebra. Scale bar = 10 mm. (download) Fig. S2. Actual images of prootic (A–D), exoccipital (E–H), and basioccipital (I–L) of Synagrops atrumoris sp. nov., non-type, CHLP2000314, 178.9 mm SL, and Synagrops japonicus (Döderlein, 1883), non-type, CHLP2000310, 174.2 mm SL showing the dorsal and ventral views. Scale bars = 5 mm. (download) Table S1. List of comparative materials of Synagrops japonicus (Döderlein, 1883) and Synagrops bellus (Goode and Bean, 1896) used in this study. (download) Table S2. Specimens of Synagrops japonicus (Döderlein, 1883) and Synagrops bellus (Goode and Bean, 1896) for morphological and meristic analysis in this study. (download) Table S3. The accession numbers of type specimens of Synagrops atrumoris sp. nov. collected in Dongsha Island, Taiwan, from trawl fishing and deposited at the Biodiversity Research Museum, Academia Sinica, and National Museum of Marine Biology and Aquarium, Pingtung. (download) page 16 of 16Zoological Studies 63:20 (2024)