New record of Melita alluaudi Ledoyer, 1982 (Amphipoda, Melitidae) from Yonaguni Island, Japan

the journal of biodiversity data NOTES ON GEOGRAPHIC DISTRIBUTION 917 Academic editor: Raquel Xavier Received: 7 August 2025 Accepted: 2 October 2025 Published: 9 October 2025 Copyright © The authors. This is an open‑access article distributed under terms of the Creative Commons Attribution License (Attribution 4.0 International – CC BY 4.0) Abstract. We report Melita alluaudi Ledoyer, 1982 from Yonaguni Island, Ryukyu Islands, Japan. These speci‑ mens represent the first record of this species from not only Japan but also from the Philippine Sea. Herein, we provide a detailed description and the cytochrome c oxidase subunit I (COI) sequences of the Yonaguni Island specimens. A key to the Japanese Melita species is also provided. Key words. COI, intertidal, Okinawa, Ryukyu Islands, taxonomy Yoshimura H, Tomikawa K (2025) New record of Melita alluaudi Ledoyer, 1982 (Amphipoda, Melitidae) from Yonaguni Island, Japan. Check List 21 (5): 917–924. https://doi.org/10.15560/21.5.917 INTRODUCTION The genus Melita Leach, 1814 occurs in marine, brackish, and freshwater environments worldwide (Tomika‑ wa et al. 2022). To date, this genus comprises 65 species (Choi and Kim 2024; Horton et al. 2025). Seventeen species of Melita have been reported from Japanese waters (Tomikawa et al. 2024): M. bingoensis Yamato, 1987; M. choshigawaensis Tomikawa, Hirashima, Hirai & Uchiyama, 2018; M. hoshinoi Yamato, 1990; M. koreana Stephensen, 1944; M. longidactyla Hirayama, 1987; M. miyakoensis Tomikawa & Aoyagi, 2022 in Tomikawa et al. (2022); M. nagatai Yamato, 1987; M. nunomurai Tomikawa & Sasaki, 2022 in Tomikawa et al. (2022); M. ogasawaraensis Tomikawa & Sasaki, 2022 in Tomikawa et al. (2022); M. okinawaensis Tomikawa & Nakano, 2022 in Tomikawa et al. (2022); M. panda Tomikawa, Yamato & Ariyama, 2024; M. pilopropoda Hirayama, 1987; M. quadridentata Yamato, 1990; M. rylovae Bulyčeva, 1955; M. setiflagella Yamato, 1988; M. shimizui (Uéno, 1940); and M. tuberculata Nagata, 1965. However, taxonomic studies of Melita remain scarce in most regions of Japan. In particular, records from the Ryukyu Islands are limited, with only M. okinawaensis previously known from brackish waters of Okinawa Island (Tomikawa et al. 2022). Recently, Melita alluaudi Ledoyer, 1982 was collected for the first time from the intertidal zone of Yona‑ guni Island in the Ryukyu Islands (Figure 1). This finding represents not only the first record of M. alluaudi in Japan but also the first record of this species from the Philippine Sea. In the present study, we provide a detailed description and illustrations of specimens from Yonaguni Island, together with mitochondrial cytochrome c oxidase subunit I (COI) sequences for future taxonomic and phylogenetic studies. In addition, we present a dichotomous key to facilitate the identification of Japanese Melita species. METHODS The specimens were collected from under the dead coral (indicated by an arrow in Figure 1C) located on an intertidal sand flat exposed to low tide. While still alive, some specimens were photographed using a digital camera (EOS M6; Canon, Tokyo, Japan) with a lens (LAOWA 65 mm f/2.8 Macro Photo Lens; Venus Optics, Heifei, China). After photographs were taken, the specimens were fixed and preserved in 99% ethanol. All appendages of examined specimens were dissected in 50% ethanol and mounted in gum‑chloral medium on glass slides under a stereomicroscope (SZ61; Olympus, Tokyo, Japan). The specimens were examined using a light microscope (Eclipse Ni‑U; Nikon, Tokyo, Japan) and illustrated with the aid of a camera lucida (Y‑IDT Drawing Tube; Nikon, Tokyo, Japan). Body length, which was measured from the rostrum tip to the base of the telson along the dorsal curvature, was recorded to the nearest 0.1 mm. The examined specimens are deposited in the National Museum of Nature and Science, Tsukuba (NSMT). 21 (5) · https://doi.org/10.15560/21.5.917 21 (5): 917–924 New record of Melita alluaudi Ledoyer, 1982 (Amphipoda, Melitidae) from Yonaguni Island, Japan Hiro Yoshimura1, Ko Tomikawa1 1 Graduate School of Humanities and Social Sciences, Hiroshima University, Higashihiroshima, Hiroshima, Japan Corresponding author: Hiro Yoshimura ([email protected]) Check List 21 (5) · https://doi.org/10.15560/21.5.917 Yoshimura and Tomikawa · Melita alluaudi from Japan 918 Genomic DNA was extracted from muscles of pereonites and pleonites, using the protocol described by Tomikawa et al. (2014). The primer set used for polymerase chain reaction (PCR) and cycles sequencing (CS) was LCO1490 and HCO2198 designed by Folmer et al. (1994). PCR and CS were performed according to the methods described by Yoshimura and Tomikawa (2025). The DNA sequences are deposited with the Inter‑ national Nucleotide Sequence Database (INSD) through the DNA Data Bank of Japan (DDBJ). DDBJ accession numbers are LC887590 and LC887591. RESULTS Family Melitidae Genus Melita Leach, 1814 Melita alluaudi Ledoyer, 1982 New Japanese name: ナンヨウメリタヨコエビ (Nanyou‑merita‑yokoebi) Figures 2–6 Melita alluaudi Ledoyer 1982: 567, fig. 215—Ren 2012: 266, fig. 116. New record. JAPAN — Okinawa Prefecture • Ryukyu Islands, Yonaguni Island, Kataburu Beach; 24°26′26″N, 122°58′26″E; intertidal zone; 17.III.2025; H. Yoshimura leg.; under a dead coral (Figure 1); 1 ♂, slide, NSMT‑Cr 33011, DDBJ: LC887590; 1 ♀, slide, NSMT‑Cr 33012, DDBJ: LC887591; 1 ♂, slide, NSMT‑Cr 33013; 1 ♀, slide, NSMT‑Cr 33014. Description of male, 9.1 mm (NSMT‑Cr 33011). Head (Figure 2A) lateral cephalic lobe rounded; antennal sinus incised. Pereonites 1–7 (Figure 2A) dorsally smooth. Epimeral plates 1–3 (Figure 3A–C) with 1, 2, and 2 short setae on posterior margins, respectively; epimeral plate 3 posterodistal corner produced, ventral margin with 3 robust setae. Pleonites 1–3 (Figure 3D) dorsal margins without teeth, each with 4 short setae. Urosomite 1 (Figure 3D) dorsal margin without teeth, with 2 short setae. Urosomite 2 (Figures 2B, 3D) with a minute dorsal tooth and 3 robust setae on each side. Antenna 1 (Figure 3E, F) length 0.6× body length; length ratio of peduncular articles 1–3 as 1.0: 1.2: 0.4; peduncular article 1 posterodistal corner with robust seta; posterior margin of peduncular article 2 with 6 clusters of slender and robust setae; primary flagellum 27‑articulate; accessory flagellum (Figure 3F) 5‑artic‑ ulate, terminal article tiny. Antenna 2 (Figure 3G) length 0.7× length of antenna 1; gland cone of peduncular Figure 1. Collecting locations and habitat of Melita alluaudi Ledoyer, 1982. A. Collecting locations reported in the previous studies (circle) and the present study (star). B. Location of the collection site in the present study, Yonaguni Island. C. Habitat on Yonaguni Island. Map data from the Natural Earth (https://www. naturalearthdata.com/). Check List 21 (5) · https://doi.org/10.15560/21.5.917 Yoshimura and Tomikawa · Melita alluaudi from Japan 919 Figure 2. Melita alluaudi Ledoyer, 1982, male, 9.1 mm (NSMT‑Cr 33011). A. Habitus, lateral view. B. Robust setae on dorsal margin of urosomite 2, lateral view. C. Dactylus of left pereopods 3, lateral view. D. Dactylus of left pereopods 7, lateral view. Scale bars: A = 1.0 mm; B–D = 0.1 mm. Figure 3. Melita alluaudi Ledoyer, 1982, male, 9.1 mm (NSMT‑Cr 33011). A–C. Right epimeral plates 1–3, lateral views. D. Dorsal margins of pleonites 1–3 and urosomites 1, 2, dorsal view. E. Right antenna 1, medial view. F. Right accessory flagellum, medial view. G. Right antenna 2, medial view. H. Upper lip, anterior view. I. Incisor, lacinia mobilis, accessory setal row, and molar process of left mandible, dorsal view. J. Right mandible, medial view. K. Lower lip, ventral view. L. Left maxilla 1, dorsal view. M. Right maxilla 2, ventral view. N. Maxilliped, dorsal view. Scale bars: A–E, G = 0.2 mm; F, H–N = 0.1 mm. Check List 21 (5) · https://doi.org/10.15560/21.5.917 Yoshimura and Tomikawa · Melita alluaudi from Japan 920 article 2 reaching half of peduncular article 3; peduncular article 3 with robust setae on medial surface and posterodistal corner; peduncular articles 4 and 5 almost same length; flagellum 12‑articulate. Upper lip (Figure 3H) ventral margin bearing short setae. Mandible (Figure 3I, J) with left and right in‑ cisors bearing 5 and 4 dentate, respectively; left lacinia mobilis 4‑dentate, right lacinia mobilis with 2 large and several small dentate; accessory setal row comprising 7 setae on the left and 6 setae on the right; molar process triturative with plumose seta; palp 3‑articulate; article 1 without setae, article 2 and 3 with 12 and 15 setae, respectively. Lower lip (Figure 3K) with outer lobes laterally expanded, bearing apical setae; inner lobes rounded, reduced. Maxilla 1 (Figure 3L) with inner plate bearing 8 plumose setae; outer plate with 9 dentate robust setae; palp 2‑articulate, outer margins bare. Maxilla 2 (Figure 3M) inner plate without oblique inner row of setae. Maxilliped (Figure 3N) inner plate bearing plumose setae on apical and inner margins, with robust seta at innerdistal corner; outer plate obovate, with 4 plumose setae on apical margin, spatula plumose setae on apical and inner margins, respectively, bearing slender setae on ventral inner submargin, reaching three fourths of palp article 2; palp 4‑articulate, article 2 medial margin with 2 rows of setae, apical margin of article 3 and inner margin of article 4 covered with fine setae. Gnathopod 1 (Figure 4A–C) ventral margin of coxa with small setae; basis anterior and posterior margins with long setae, posterodistal submargin covered with fine setae laterally and medially; ischium and merus posterior margins covered with fine setae laterally and medially; carpus length 1.6× length of propodus, Figure 4. Melita alluaudi Ledoyer, 1982, male, 9.1 mm (NSMT‑Cr 33011). A. Left gnathopod 1, medial view. B, C. Palmar margin of propodus and dactylus of left gnathopod 1, lateral and medial view, respectively. D. Right gnathopod 2, medial view. Scale bars: A, D = 0.3 mm; B, C = 0.1 mm. Check List 21 (5) · https://doi.org/10.15560/21.5.917 Yoshimura and Tomikawa · Melita alluaudi from Japan 921 anterodistal corner covered with fine setae medially, and bearing row of weakly plumose setae; propodus anterodistal projection forming rectangular hood, covering dactylus (Figure 4B, C), with 2 (left gnathopod 1) or 3 (right gnathopod 1) robust setae at the base of anterodistal projection projecting vertically toward the medial side, posterodistal corner with 2 robust and 7 slender setae, a rounded hump at the base of posterodistal corner rising vertically in the medial direction; tip of dactylus directed medially, anteroproxi‑ mal margin, anterodistal margin, and posterodistal margin with seta, respectively. Gnathopod 2 (Figure 4D) ventral margin of coxa with small setae; basis posterior margin with long setae; propodus subrectangular, medial surface with dense, slender setae, with a ridge running from the base of dactylus toward medial surface, with 3 robust setae on medial surface between a ridge and dactylus, palmar margin oblique with a row of robust setae. Pereopods 3, 4 (Figure 2A) ventral margins of coxa with small setae; basis anteroproximal and posterior margins with long setae; dactylus (Figure 2C) with plumose seta on anteroproximal margin, a slender seta on posterior margin and at base of nail, respectively. Pereopods 5–7 (Figure 2A) basis expanded, anterior margin bearing a series of small robust setae, posterior margin weakly serrate; merus weakly expanded, length 1.8, 1.8, 2.0× width, respectively; dactylus (Figure 2D) with plumose seta on posteroproximal margin, with slender seta on anterior margin and at the base of nail, respectively; coxal plate 5 biobate, with small seta on distal margin of anterior lobe; coxal plate 6 biobate, with small seta on anterior margin of anterior Figure 5. Melita alluaudi Ledoyer, 1982, (A–D) male, 9.1 mm (NSMT‑Cr 33011), (E–I) female, 6.2 mm (NSMT‑Cr 33012), and (J) female, 6.0 mm (NSMT‑Cr 33014). A. Left uropod 1, lateral view. B. Left uropod 2, lateral view. C. Left uropod 3, dorsal view. D. Telson, dorsal view. E. Left gnathopod 1, lateral view. F. Palmar margin of propodus and dactylus of right gnathopod 1, medial view. G. Left gnathopod 2, lateral view. H. Palmar margin of propodus and dactylus of right gnathopod 2, medial view. I, J. Pereopod 6 coxa, lateral view. Scale bars: A–C, E, G = 0.3 mm; D, F, H–J = 0.1 mm. Check List 21 (5) · https://doi.org/10.15560/21.5.917 Yoshimura and Tomikawa · Melita alluaudi from Japan 922 lobe and posterior margin of posterior lobe, respectively; coxal plate 7 semicircular, with small seta on pos‑ terior margin. Coxal gills (Figure 2A) present on gnathopod 2, and pereopods 3–6. Uropod 1 (Figure 5A) peduncle length 1.2× length of rami, with 8 dorsolateral, 3 dorsomedial, and 1 basofacial robust setae; outer ramus almost as long as inner ramus, with 4 and 3 robust setae on lateral and medial margins, respectively, distal part with 4 robust setae; inner ramus with 3 lateral, 4 medial, and 5 apical robust setae. Uropod 2 (Figure 5B) peduncle length 1.1× length of outer ramus, with 5 dorsolateral, and 2 dorsomedial robust setae; outer ramus length 0.9× length of inner ramus, with 5 and 2 robust setae on lateral and medial margins, respectively, distal part with 3 robust setae; inner ramus with 2 lateral, 3 medial, and 4 apical robust setae. Uropod 3 (Figure 5C) peduncle length 0.5× length of outer ramus; outer ramus broad, 2‑articulate, article 1 lateral and medial margins with 6 and 8 clusters of setae, respectively; article 2 small, length 0.05× length of article 1. Telson (Figure 5D) length 1.1× width, cleft, each lobe with 2 or 3 and 1 robust setae on lateral and medial margins, respectively, distal part with 5 robust, 2 plumose, and 1 slender setae. Sexually dimorphic characters of two females: 6.2 mm (NSMT‑Cr 33012); 6.0 mm (NSMT‑Cr 33014). Gnathopod 1 (Figure 5E, F) carpus length 1.3× length of propodus; propodus anterodistal corner not project‑ ed, palmar margin vertical, posterodistal corner with 2 or 3 robust setae medially. Gnathopod 2 (Figure 5G, H) propodus subovate, medial surface with a few slender setae, palmar margin oblique with 8 robust setae laterally, and 2 or 3 robust setae on palmar corner. Coxal plate 6 (Figure 5I, J) anterior lobe depth 1.3× width of coxa, strongly hooked, with 2 or 3 setae on anterior margin. Oostegites (Figure 5G) present on gnathopod 2, and pereopods 3–5, narrow with setae. Coloration in life. Body generally translucent (Figure 6); eyes black; antennae 1 and 2 peduncle articles distally brown. Variation. Accessory flagellum of antenna 1 4‑ or 5‑articulate. Rounded hump at base of male gnathopod 1 propodus posterodistal corner indistinct in the 7.5 mm male (NSMT‑Cr 33013). Distribution. Madagascar: Tôlanaro (Ledoyer 1982). China: Daya Bay, Guangdong; Linchang Reef, Hainan (Ren 2012). Japan: Yonaguni Island, Okinawa (present study) (Figure 1A). Identification. The specimens in the present study agree well with the original description of M. alluaudi by having the following features: 1) urosomite 1 dorsal margin not produced; 2) urosomite 2 with a minute dorsal tooth and 3 robust setae on each side; 3) epimeral plate 3 posterodistal corner produced; 4) male gnathopod 1 propodus anterodistal projection forming rectangular hood, covering the dactylus; 5) male gnathopod 2 propodus subrectangular; 6) uropod 3 outer ramus broad, 2‑articulate; and 7) telson with ro‑ bust setae on lateral margin. The original description of M. alluaudi provides only limited morphological information because the description is very brief and several appendages are unillustrated. Nonetheless, the present specimens exhibit the above diagnostic features consistent with the original description, and no distinguishing differences were found. Therefore, the specimens are identified as M. alluaudi. Figure 6. Melita alluaudi Ledoyer, 1982, male (NSMT‑Cr 33011) held female (NSMT‑Cr 33012) in precopula. Scale bar: 1.0 mm. Check List 21 (5) · https://doi.org/10.15560/21.5.917 Yoshimura and Tomikawa · Melita alluaudi from Japan 923 Key to species of Melita from Japan 1 Uropod 3 outer ramus 1‑articulate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 – Uropod 3 outer ramus 2‑articulate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 2 Pleonites 1–3 each with dorsal teeth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M. tuberculata Nagata, 1965 – Pleonites 1–3 without dorsal teeth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3 Eyes absent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M. miyakoensis Tomikawa & Aoyagi, 2022 – Eyes present . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4 Antennal sinus of head absent; pereopods 3 and 4 with long, feeble dactyli . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M. longidactyla Hirayama, 1987 – Antennal sinus of head present; pereopods 3 and 4 with short, stout dactyli . . . . . . . . . . . . . . . . . . . . . . . . 5 5 Antennal sinus of head incised . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 – Antennal sinus of head rounded or right‑angled . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 6 Antenna 2 flagellum densely setose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M. setiflagella Yamato, 1988 – Antenna 2 flagellum sparsely setose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 7 Body black‑and‑white; anterodistal projection of male gnathopod 1 propodus fully covering dactylus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M. panda Tomikawa, Yamato & Ariyama, 2024 – Body almost all gray; anterodistal projection of male gnathopod 1 propodus not completely covering dactylus ...................................................................................... 8 8 Urosomite 2 without dorsal teeth ...................................... M. koreana Stephensen, 1944 – Urosomite 2 with a minute dorsal tooth on each side .............................................. 9 9 Male gnathopod 1 propodus with robust seta on palmar corner, lacking robust setae on medial surface; female coxa 6 deeper than wide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M. nagatai Yamato, 1987 – Male gnathopod 1 propodus without robust seta on palmar corner, bearing robust setae on medial surface; female coxa 6 shallower than wide ............................ M. bingoensis Yamato, 1987 10 Telson shorter than wide ..................................... M. nunomurai Tomikawa & Sasaki, 2022 – Telson as long as or longer than wide ............................................................. 11 11 Male gnathopod 1 propodus with anterodistal hood; female coxa 6 deeper than wide; female coxae 1 and 2 with concavity in anterior edge bearing numerous setae ................................... ..................................................... M. ogasawaraensis Tomikawa & Sasaki, 2022 – Male gnathopod 1 propodus without anterodistal hood; female coxa 6 wider than deep; female coxae 1 and 2 without concavity in anterior edge ...................................................... 12 12 Male uropod 3 outer ramus approximately 5× width; female coxa 6 wider than deep .................. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M. shimizui (Uéno, 1940) – Male uropod 3 outer ramus longer than 7× width; female coxa 6 as wide as depth .................. 13 13 Male gnathopod 2 propodus proximally elevated; female gnathopod 2 basis with small palmate setae . M. okinawaensis Tomikawa & Nakano, 2022 – Male gnathopod 2 propodus not proximally elevated; female gnathopod 2 basis without small palmate setae . . . . . . . . . . . . . . . . . . . . . . . . . . . M. choshigawaensis Tomikawa, Hirashima, Hirai & Uchiyama, 2018 14 Uropod 3 outer ramus with long setae ................................ M. quadridentata Yamato, 1990 – Uropod 3 outer ramus without long setae ......................................................... 15 15 Maxilla 1 palp article 1 without setae; male gnathopod 2 propodus with squarish palmar corner ...... 16 – Maxilla 1 palp article 1 with setae; male gnathopod 2 propodus with transverse palmar margin ...... 17 16 Pleonites 1–3 with dorsal teeth .............................................. M. rylovae Bulyčeva, 1955 – Pleonites 1–3 without dorsal teeth .......................................... M. alluaudi Ledoyer, 1982 17 Setae on maxilla 1 palp article 1 reaching distal part of palp article 2; pereopods 5–7 with basis not ex‑ tremely expanded, length more than 1.3× width ........................ M. hoshinoi Yamato, 1990 – Setae on maxilla 1 palp article 1 not reaching distal part of palp article 2; pereopods 5–7 with basis ex‑ tremely expanded, length less than 1.3× width ..................... M. pilopropoda Hirayama, 1987 DISCUSSION Melita alluaudi was originally described by Ledoyer (1982) based on specimens from Madagascar. Subse‑ quently, Ren (2012) recorded this species in southern China. The present study represents the third record of M. alluaudi and the first record from Japan and the Philippine Sea. Ren (2012) described M. alluaudi based on the specimens collected from beneath stones on shallow coral reefs, and his description shows no sig‑ nificant differences from the material examined our study. Notably, the environment where Ren collected Check List 21 (5) · https://doi.org/10.15560/21.5.917 Yoshimura and Tomikawa · Melita alluaudi from Japan 924 his specimens is similar to the habitat in which our specimens were found. Thus, by conducting surveys in same habitats, M. alluaudi could be discovered in other regions where this species has not been recorded. The original description of M. alluaudi lacks morphological information for several appendages. For example, maxilla 2 and female coxa 6, which are diagnostic features of other Melita species, were not de‑ scribed. Since M. alluaudi has been subsequently recorded from China and Japan, it is necessary to clarify its diagnostic characters using materials from both the type locality and newly recorded regions. In the future, it will be desirable to redescribe the type material and supplement the missing data. ACKNOWLEDGEMENTS We are grateful to Vjacheslav S. Labay, Benoit Gouillieux, and Young‑Hyo Kim for their constructive and valuable comments on this manuscript. We also thank Raquel Xavier for editing a draft of this manuscript. We appreciate the Natural Science Center for Basic Research and Development for providing access to the experimental equipment. ADDITIONAL INFORMATION Conflict of interest The authors declare that no competing interests exist. Ethical statement No ethical statement is reported. Funding This study was financially supported by the Japan Society for the Promotion of Science (JSPS) through a Grant‑in‑Aid for JSPS Fellows [25KJ1881] to HY and JSPS KAKENHI grants [22K06373 and 23K22282] to KT. Author contributions Conceptualization: HY. Data curation: HY, KT. Formal analysis: HY. Funding acquisition: HY, KT. Investigation: HY. Methodology: HY, KT. Resources: HY. Supervision: KT. Visualization: HY. Project administration: HY, KT. Software: HY. Validation: HY, KT. Writing – original draft: HY, KT. Writing – review and editing: HY, KT. Author ORCID iDs Hiro Yoshimura https://orcid.org/0009‑0005‑1297‑4368 Ko Tomikawa https://orcid.org/0000‑0003‑1521‑9016 Data availability All data that support the findings of this study are available in the main text. REFERENCES Choi JH, Kim YH (2024) A new species of the genus Melita (Crustacea, Amphipoda, Melitidae) and a new record for Melita shimizui from Korean Brackish Waters. Zootaxa 5551 (3): 512–530. https://doi.org/10.11646/zootaxa.5551.3.4 Folmer O, Black M, Hoeh W, Lutz R, Vrijenhoek R (1994) DNA primers for amplification of mitochondrial cytochrome c oxidase subunit I from diverse metazoan invertebrates. Molecular Marine Biology and Biotechnology 3: 294–299. 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