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Research Article
Melita panda, a new species of Melitidae (Crustacea, Amphipoda) from Japan
expand article infoKo Tomikawa‡, Shigeyuki Yamato§, Hiroyuki Ariyama|
‡ Hiroshima University, Higashihiroshima, Japan
§ Unaffiliated, Wakayama, Japan
| Osaka Museum of Natural History, Osaka, Japan

Corresponding author: Ko Tomikawa ( tomikawa@hiroshima-u.ac.jp )

Academic editor: Alan Myers
© 2024 Ko Tomikawa, Shigeyuki Yamato, Hiroyuki Ariyama.
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: Tomikawa K, Yamato S, Ariyama H (2024) Melita panda, a new species of Melitidae (Crustacea, Amphipoda) from Japan. ZooKeys 1212: 267-283. https://doi.org/10.3897/zookeys.1212.128858
ZooBank: urn:lsid:zoobank.org:pub:1E358CD5-227D-445D-8177-CFEEDF057D1A
Open Access

Abstract

A new intertidal species of the melitid amphipod, Melita panda, from the Wakayama Prefecture, Japan, is identified and described. Melita panda sp. nov. differs from the similar M. koreana and M. nagatai by its black-and-white body color, well-developed anterodistal projection of the male gnathopod 1 propodus, and telson armature. Molecular phylogenetic analyses based on the nuclear 28S rRNA and mitochondrial COI genes support that M. panda sp. nov. is closely related to M. koreana and M. nagatai.

Key words

Intertidal zone, Melita panda, molecular phylogeny, morphology, systematics, taxonomy, Wakayama

Introduction

Melita Leach, 1814, encompasses melitid amphipods found in marine, brackish, and freshwater environments. It includes 63 described species worldwide (Krapp-Schickel and Sket 2015; Labay 2016; Tomikawa et al. 2018, 2022; Horton et al. 2024). Sixteen species of the genus have been recorded in Japan: 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. 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 in the Japanese Archipelago are insufficient, and many undescribed species still remain.

In the 1990s, one of the authors (SY) found an unidentified species of Melita recognized by the characteristic black-and-white body coloration from the intertidal zone of Wakayama Prefecture, Japan. This species was treated as Melita sp. 1 by Ariyama (2022). Recently, a significant number of specimens of this species have been accumulated by the first and third authors (KT and HA). Detailed morphological analysis revealed that this species has not been previously described; therefore, it is described and named here. In recent years, molecular phylogenetic analyses have been used to elucidate the phylogenetic relationships among species of Melita (Tomikawa et al. 2022). The phylogenetic positions of the newly identified species in this study are also clarified.

Material and methods

Sampling and morphological observation

Samples of the undescribed Melita species were collected from intertidal waters in Wakayama Prefecture, Japan. Samples were collected by passing a hand-net over cobble and sand substrates, and the amphipods were later sorted. The samples were fixed and preserved in 99% ethanol at the site.

All appendages were dissected in 80% ethanol and mounted in a gum-chloral medium on glass slides using a stereomicroscope (Olympus SZX7). Slides were examined using a light microscope (Nikon Eclipse Ni), with appendages illustrated using a camera lucida (Nikon Y-IDT). Male gnathopod 1 and female pereopod 6 were dehydrated through a graded ethanol series, and dried using hexamethyldisilazane (HMDS) (Nation 1983). They were then sputter-coated with gold and observed using scanning electron microscopy (SEM, JSM-6510LV). Body length was measured from the rostrum tip to the telson base, along the dorsal curvature to the nearest 0.1 mm. Type specimens are deposited in the National Museum of Nature and Science, Tsukuba (NSMT).

Molecular phylogeny

Genomic DNA was extracted from the appendage muscles of the samples following procedures detailed by Tomikawa et al. (2014b) and Tomikawa et al. (2014a). The primer sets for PCR and cycle sequencing reactions used in this study were as follows: 28SF and 28SR (Tomikawa et al. 2012) for 28S rRNA (28S), H3aF and H3bR (Colgan et al. 2000) for histone H3 (H3), and LCO1490 and HCO2198 (Folmer et al. 1994) for cytochrome c oxidase subunit I (COI). PCR and DNA sequencing were performed using the method detailed by Tomikawa (2015). The newly obtained DNA sequences were deposited in the International Nucleotide Sequence Databases (INSD) through the DNA Data Bank of Japan (DDBJ) (Table 1).

Table 1.
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Information and GenBank accession numbers of specimens studied in the present study. Sequences marked with an asterisk were newly obtained in this study.

Species Voucher or isolate number Locality Coordinates (decimal degrees) GenBank accession numbers
COI 28S histone H3
Melita shimizui G652 Ota River, Hiroshima, Japan 32.4050°N, 132.4371°E LC371928 LC637781 LC637944
Melita okinawaensis NSMT-Cr 29115 Shiokawa, Motobu, Okinawa, Japan 26.6158°N, 127.8950°E LC637583 LC637782 LC637945
Melita choshigawaensis G1391 Choshi River, Kihoku, Mie, Japan 34.1082°N, 136.2219°E LC371923 LC637783 LC637946
Melita nagatai G1392 Etajima, Hiroshima, Japan 34.1461°N, 132.4400°E LC637584 LC637784 LC637947
Melita setiflagella G1393 Numata River, Mihara, Hiroshima, Japan 34.3889°N, 133.0528°E LC637585 LC637785 LC637948
Tegano shiodamari G1418 Unbuki Cave, Tokunoshima I., Kagoshima, Japan 27.8269°N, 128.8810°E LC637586 LC637787 LC637950
Melita nunomurai NSMT-Cr 29091 Stream near Osawa Beach, Haha-jima, Ogasawara, Japan 26.6987°N, 142.1349°E LC637587 LC637788 LC637951
Melita ogasawaraensis NSMT-Cr 29100 Stream at Hatsuneura, Chichi-jima, Ogasawara, Japan 27.0807°N, 142.2245°E LC637591 LC637792 LC637955
Melita panda sp. nov. NSMT-Cr 32146 (G1489) Jogasaki, Wakayama, Japan 34.2850°N, 135.0680°E *LC815081 *LC815084 *LC815087
Melita panda sp. nov. NSMT-Cr 32145 (G1491) Tagurazaki, Wakayama, Japan 34.2666°N, 135.0608°E *LC815082 *LC815085 *LC815088
Melita panda sp. nov. NSMT-Cr 32147 (G1492) Jogasaki, Wakayama, Japan 34.2850°N, 135.0680°E *LC815083 *LC815086 *LC815089
Melita rylovae G1766 Shijushima I. Mukaishima, Onomichi, Hiroshima, Japan 34.3608°N, 133.1630°E LC637597 LC637798 LC637961
Abludomelita klitinii G1767 Aidomari, Shiretoko, Hokkaido, Japan 44.1851°N, 145.3180°E LC637598 LC637799 LC637962
Melita koreana G1769 Sasebo River, Sasebo, Nagasaki, Japan 33.1663°N, 129.7196°E LC637600 LC637801 LC637964
Melita hoshinoi G1770 Iyo-nada, Seto Inland Sea, Japan 33.4378°N, 131.8478°E LC637601 LC637802 LC637965
Melita miyakoensis NSMT-Cr 29084 Miyahara, Hirara, Miyakojima, Okinawa, Japan 24.7830°N, 125.3372°E LC637605 LC637806 LC637969
Abludomelita japonica G1806 Toyokunisaki, Misaki, Osaka, Japan 34.3227°N, 135.1163°E LC637611 LC637812 LC637975
Dulichiella tomioka G262 Off Tanegashima Island, Kagoshima, Japan 30.8958°N, 131.0430°E LC637612 LC637813 LC637976
Elasmopus nkjaf G1337 Miyako Island, Okinawa, Japan 24.7997°N, 125.3341°E LC215813 LC215811 LC215815
Gammarella cyclodactyla G1421 Kamikamagari Island, Kure, Hiroshima, Japan 34.1731°N, 132.7375°E LC637613 LC637814 LC637977
Victoriopisa ryukyuensis G1802 Lake Manko, Naha, Okinawa, Japan 26.1936°N, 127.6816°E LC637614 LC637815 LC637978
Megamoera dentata – Quebec, Canada 50.25°N, 66.70°W FJ581757 – –
Quasimelita formosa – Quebec, Canada 50.25°N, 66.70°W FJ581763 – –
Melita hergensis – Minho, Litoral Norte, Viana do Castelo, Praia Norte, Portugal 41.694°N, 8.851°W KX224061 – –
Melita nitida – Virginia, Eastern Shore, USA 37.606°N, 75.6254°W MH826287 – –
Megamoera subtener – British Columbia, Haida Gwaii, Skidegate, Canada 53.2676°N, 131.977°W MG936114 – –
Megamoera dentata – Washington, San Juan County, Lopez Island, USA 48.5489°N, 122.926°W MH242844 – –
Exitomelita lignicola – Norwegian Sea 73.5532°N, 8.282°E JQ775392 – –
Exitomelita sigynae – Norwegian Sea 73.5668°N, 8.1604°E JN831764 – –

The phylogenetic analyses were conducted based on sequences of nuclear 28S and H3, and mitochondrial COI. Three species, Victoriopisa ryukyuensis Morino, 1991 (Eriopisidae), Elasmopus nkjaf Nakamura, Nakano, Ota & Tomikawa, 2019 (Maeridae), and Gammarella cyclodactyla (Hirayama, 1978) (Nuuanuidae), were included in the analyses as outgroup taxa. The alignment of H3 and COI was trivial, as no indels were observed. The 28S sequences were aligned using the Muscle algorithm using the software MEGA11 (Tamura et al. 2021). The lengths of the 28S, H3 and COI were found to be 1001, 331 and 658 bp, respectively. The concatenated sequences yielded 1990 bp of alignment positions.

Phylogenetic relationships were reconstructed via maximum likelihood (ML) and Bayesian inference (BI), and partitioned by 28S, H3, and the 1st, 2nd, and 3rd codon positions for COI. The best evolutionary models were selected based on the corrected Bayesian information criterion (BIC) using ModelFinder (Kalyaanamoorthy et al. 2017): for 28S, TIM3+F+G4; for H3, TNe+G4; for COI, TPM3+F+G4. ML phylogenies were conducted using IQ-TREE web server (ver. 1.6.12, see http://www.iqtree.org/; Trifinopoulos et al. 2016) with 1000 ultrafast bootstrap replicates (Hoang et al. 2018) performed to estimate statistical support for branching patterns with 1000 replicates. The BI tree and Bayesian posterior probabilities were estimated using MrBayes ver. 3.2.6 (Ronquist et al. 2012), with Markov chains of 10 million generations. Parameter estimates and convergence were checked using Tracer ver. 1.7.1 (Rambaut et al. 2018), and the first 1 million trees were discarded as burn-in.

Results

Systematics

Family Melitidae Bousfield, 1973

Genus Melita Leach, 1814

Melita panda sp. nov.

https://zoobank.org/EC735281-9AAC-4DFF-BC0D-945876A8E958
Figs 1, 2, 3, 4, 5, 6 New Japanese name: Panda-melita-yokoebi

Melita sp. 1: Ariyama, 2022: 119.

Material examined

Holotype : • male 6.0 mm (NSMT-Cr 32141); Tagurazaki, Wakayama, Japan; (34.264603°N, 135.060835°E); collected by Hiroyuki Ariyama and Ko Tomikawa; on 25 March 2019. Paratypes: • male 7.6 mm (NSMT-Cr 32142); female 4.8 mm (NSMT-Cr 32143); female 4.5 mm (SEM, NSMT-Cr 32144); data same as for the holotype • male 5.0 mm (NSMT-Cr 32145, G1491); locality same as for the holotype; collected by Hiroyuki Ariyama; on 12 July 2018 • male 5.8 mm (NSMT-Cr 32146, G1489); male 4.5 mm (NSMT-Cr 32147, G1492); Jogasaki, Wakayama, Japan; (34.2850°N, 135.0680°E); collected by Hiroyuki Ariyama; on 14 July 2018 • male 5.2 mm (NSMT-Cr 32148); female 4.3 mm (NSMT-Cr 32149); Shirahama, Wakayama, Japan; (33.691826°N, 135.336172°E); collected by Hiroki Yamada and Ko Tomikawa; on 12 November 2023.

Diagnosis

Head with eyes; antennal sinus incised. Pleonites and urosomites lacking dorsal teeth. Epimeral plate 3 with weakly pointed posterodistal corner. Urosomite 2 with 3 dorsolateral robust setae on each side without distinct teeth. Antenna 1 with 4-articulate accessory flagellum. Maxilla 1 with inner plate bearing 7 plumose setae. Gnathopod 1 with basis and ischium bearing small palmate setae. Male gnathopod 1 with anterodistal projection on propodus forming rounded hood, covering almost all of dactylus, propodus with 3 and 1 robust setae on posterior margin and at the base of anterodistal projection, respectively. Male gnathopod 2 with subquadrate propodus setaceous on medial surface, angle between posterior and palmar margins of propodus being approximately 140°. Female coxa 6 hooked with anterior lobe 1.2 times deeper than width of coxa. Uropod 3 with 1-articulate outer ramus. Telson longer than its width.

Description

Holotype, male, NSMT-Cr 32141. Head (Fig. 1) almost as long as pereonites 1 and 2 combined; rostrum short; eyes developed, oval; lateral cephalic lobe rounded; antennal sinus incised. Pereonites 1–7 (Fig. 1) dorsally smooth. Epimeral plates 1–3 (Fig. 2A–C) with 2, 2 and 3 short setae on posterior margin; epimeral plate 3 posterodistal corner weakly produced, ventral margin with 5 robust setae. Pleonites 1–3 dorsal margins without teeth, each with 4 short setae and that of urosomite 1 with 2 short setae (Fig. 2D); dorsal margin of urosomite 2 with 3 robust setae on each side (Fig. 2D).

Figure 1. 

Melita panda sp. nov. holotype, male 6.0 mm (NSMT-Cr 32141), habitus, lateral view.

Figure 2. 

Melita panda sp. nov. holotype, male 6.0 mm (NSMT-Cr 32141) A–C epimeral plates 1–3, lateral views D dorsal margins of pleonites 1–3 and urosomites 1–2, dorsal view E antenna 1, lateral view, some articles of main flagellum omitted F antenna 2, lateral view G upper lip, anterior view H right mandible, medial view I incisor and lacinia mobilis of left mandible, lateral view J incisor and lacinia mobilis of right mandible, medial view K lower lip, dorsal view L left maxilla 1, ventral view M apical part of right maxilla 1, ventral view N maxilla 2, dorsal view O maxilliped, dorsal view.

Antenna 1 (Fig. 2E) length 0.7 times that of body; length ratio of peduncular articles 1–3 as 1.0: 1.3: 0.5; ventral margin of peduncular article 1 with 3 robust setae, posterodistal corner with robust seta; primary flagellum 23-articulate with a few setae; accessory flagellum 4-articulare, terminal article short. Antenna 2 (Fig. 2F) length 0.6 times that of antenna 1; peduncular article 2 with robust seta on anterodistal corner; peduncular article 3 with robust setae on medial surface and posterodistal corner; peduncular articles 4 and 5 with 4 clusters of setae on posterior margins, peduncular article 5 1.1 times as long as article 4; flagellum 8-articulate, article 1 2.3 times as long as article 2; calceoli absent.

Upper lip (Fig. 2G) with convex, rounded ventral margin bearing minute setae. Left and right mandible with 5-dentate incisor (Fig. 2H–J); left lacinia mobilis (Fig. 2I) 4-dentate, right lacinia mobilis (Fig. 2J) with 2 large and several small teeth; left and right accessory setal rows each with five-bladed setae and plumose seta; molar process triturative with plumose seta; palp tri-articulate, length ratio of articles 1–3 1.0: 2.3: 2.3, article 1 marginally bare, article 2 with 10 setae on ventral margin, article 3 with 12 and 3 setae on ventral and dorsal margins, respectively. Lower lip (Fig. 2K) with broad outer lobes bearing minute setae, mandibular lobes narrow; inner lobes indistinct. Maxilla 1 (Fig. 2L, M) with inner plate bearing 7 plumose setae; outer plate rectangular with 9 serrate robust setae; palp 2-articulate; article 1 with 3 long setae on laterodistal corner; article 2 arched, outer margin bare, apical margin with robust and slender setae. Maxilla 2 (Fig. 2N) with inner plate lacking oblique inner row of setae; outer plate slightly longer than inner plate. Maxilliped (Fig. 2O) with inner plate not reaching half of palp article 2, bearing 3 robust setae distally; outer plate ovate, exceeding half of palp article 2, apical margin with plumose setae, inner submargin with robust setae; palp 4-articulate, medial margin of article 2 lined with setae, article 3 weakly expanded medially, article 4 with fine facial setae and nail.

Gnathopod 1 (Fig. 3A, B) smaller than gnathopod 2; coxa weakly expanded ventrally, ventral margin with setae; basis, anterior and posterior margins with long setae, posterodistal submargin with tiny palmate setae; ischium with tiny palmate setae; merus ventral margin with small setae; carpus not lobate, length 1.2 times that of propodus, anterodistal corner with palmate setae, posterior margin with clusters of setae; propodus 1.9 times as long as wide, anterodistal projection forming hood, covering almost all of dactylus (Figs 3B, 6A), robust seta at the base of anterodistal projection, posterior margin with 3 robust setae, palmar margin with slender setae; dactylus short, not exceeding palmar margin. Gnathopod 2 (Fig. 3C, D) with subrectangular coxa, bearing setae on ventral margin; basis with long setae at anterodistal corner and on posterior margin, posterodistal submargin without palmate setae; ischium without palmate setae; carpus not lobate, length 0.4 times of that of propodus; propodus large, subquadrate, length 1.5 times as long as wide, angle between posterior and palmar margins being approximately 140°, medial surface setaceous, palmar margin oblique with robust setae becoming thinner toward end; dactylus not exceeding palmar margin.

Figure 3. 

Melita panda sp. nov. holotype, male 6.0 mm (NSMT-Cr 32141) A gnathopod 1, lateral view B palmar margin of propodus and dactylus of gnathopod 1, medial view C gnathopod 2, medial view D palmar margin of propodus and dactylus of gnathopod 2, medial view E pereopod 3, lateral view F pereopod 4, lateral view.

Pereopod 3 (Fig. 3E) with subrectangular coxa, ventral margin with setae; basis arched, anterior margin with short setae, posterior margin with long and short setae; length ratio of merus, carpus, propodus and dactylus 1.0: 0.9: 0.9: 0.3; merus with robust setae on anterior margin, carpus and propodus with robust setae on posterior margins. Pereopod 4 (Fig. 3F) with expanded coxa bearing posterior concavity, with ventral setae; basis weakly arched, anterior and posterior margins with long and short setae; length ratio of merus, carpus, propodus and dactylus 1.0: 0.8: 0.9: 0.3; carpus and propodus with robust setae on posterior margins. Pereopod 5 (Fig. 4A) with bilobate coxa, anterior lobe large with small seta on anterior margin, posterior lobe with small setae on posterior margin; basis ovate with posterodistal lobe, anterior margin with robust setae, posterior margin with short setae; merus weakly expanded, length 2.2 times as long as wide. Pereopod 6 (Fig. 4B) with bilobate coxa, anterior lobe marginally bare, posterior lobe with small seta on ventral margin and posterodistal corner; basis slender, ovate, anterior margin with robust setae, posterior margin with short setae, posterodistal corner lobate; merus length 2.4 times as long as wide. Pereopod 7 (Fig. 4C) with coxa, bearing seta on posterior margin; basis subovate, anterior margin with robust setae, posterior margin weakly serrate with short setae, posterodistal corner lobate; merus length 2.1 times as long as wide.

Figure 4. 

Melita panda sp. nov. holotype, male 6.0 mm (NSMT-Cr 32141) A pereopod 5, lateral view B pereopod 6, lateral view C pereopod 7, lateral view D pleopod 1, medial view.

Coxal gills present on gnathopod 2, and pereopods 3–6.

Pleopods 1–3 (Fig. 4D) peduncles with paired retinacula on inner distal margin and facial setae; inner ramus with bifid plumose setae (clothes-pin setae) on inner basal margin.

Uropod 1 (Fig. 5A) extending beyond uropod 2; peduncle length 1.3 times longer than inner ramus, with basofacial robust seta; inner ramus almost as long as outer ramus, with 3 inner and 2 outer marginal robust setae; outer ramus with 3 robust setae on inner and outer margins, respectively. Uropod 2 (Fig. 5B) not extending beyond peduncle of uropod 3; peduncle length 1.1 times longer than inner ramus; inner ramus almost as long as outer ramus, with 2 and 1 robust setae on inner and outer margins, respectively; outer ramus with 2 inner and 4 outer marginal robust setae. Uropod 3 (Fig. 5C) with peduncle not extending beyond telson, 0.4 times as long as outer ramus; inner ramus length 0.2 times that of outer ramus, with subdistal robust seta; outer ramus with single article, straight, length 5.4 times that of outer ramus width, inner and outer margins each with 5 clusters of robust setae, distal part with robust and slender setae, longest distal slender seta shorter than longest distal robust seta.

Figure 5. 

Melita panda sp. nov. A–E holotype, male 6.0 mm (NSMT-Cr 32141) F–K paratype, female 4.8 mm (NSMT-Cr 32143) A uropod 1, dorsal view B uropod 2, dorsal view C uropod 3, dorsal view D uropod 3 distal part of outer ramus, dorsal view E telson, dorsal view F gnathopod 1, medial view G palmar margin of propodus and dactylus of gnathopod 1, medial view H gnathopod 2, lateral view I palmar margin of propodus and dactylus of gnathopod 2, medial view J oostegite on gnathopod 2, medial view K pereopod 6 coxa, lateral view.

Telson (Fig. 5E) length 1.1 times longer than wide, almost completely cleft, each lobe with 1 medial, 4–5 subdistal and 3 lateral robust setae.

Female (paratype, NSMT-Cr 32143), sexually dimorphic characters. Gnathopod 1 (Fig. 5F, G) with carpus length 1.2 times that of propodus; propodus palmar margin vertical, with 2 rows of slender setae, palmar angle with robust seta. Gnathopod 2 (Fig. 5H, I) with elongate coxa; carpus length 0.8 times that of propodus; propodus 1.7 times as long as wide, palmar margin oblique, with 4 robust setae along palmar margin and 2 robust setae on palmar corner.

Coxa of pereopod 6 (Figs 5K, 6B, C) with anterior lobe 1.2 times deeper than width of coxa, strongly hooked, bearing slit-like shallow “pocket” at base, trailing edge near tip of anterior lobe loosely turned up.

Figure 6. 

SEM photographs of Melita panda sp. nov. A propodus and dactylus of male gnathopod 1, medial view B coxa of female pereopod 6, lateral view, dorsal surface partly damaged C distal part of coxa of female pereopod 6, lateral view. A paratype male 7.6 mm, NSMT-Cr 32142 B and C paratype female 4.5 mm, NSMT-Cr 32144.

Oostegites (Fig. 5J) present on gnathopod 2 and pereopods 3–5, narrow with setae.

Coloration in life

Black pattern on white background. The black pattern is found in the following areas: antennae 1 and 2 peduncular articles; part of head, pereonites 1, 2, 3 (part), 5–7; coxae 1, 2, 3 (part), 5 (part), 6, 7; distal part of gnathopod 2 propodus; posterior half of bases of pereopods 5–7; dorsal part of pleonites 1 and 2, urosomite 1 posterior half, urosomites 2 and 3; and uropods 1 and 2 peduncles, uropod 3. Coloration is almost identical between males and females, but females lack the black area on gnathopod 2. Colors remain largely unchanged after ethanol fixation.

Etymology

The species name “panda” is derived from its black-and-white body coloration, which resembles that of the giant panda Ailuropoda melanoleuca.

Molecular phylogeny

The obtained ML tree exhibited a topology almost identical to that of the BI tree (Fig. 7). Melitidae formed a monophyletic group with high statistical support (USB = 99%, BPP = 0.99). The monophyly of Melita was supported by the BI tree (BPP = 0.93) but less so by the ML tree (USB = 0.68). Melita panda sp. nov. was the sister taxon of M. nagatai and M. koreana among the 14 species of Melita used in the analyses (USB = 98%, BPP = 1.0). These three species formed a monophyletic group with M. hoshinoi (USB = 99%; BPP = 0.99).

Figure 7. 

Maximum likelihood tree for 1990 bp of nuclear 28S rRNA, histone H3, and mitochondrial cytochrome c oxidase subunit I markers. Numbers at nodes represent ultrafast bootstrap values for maximum likelihood and Bayesian posterior probabilities.

Discussion

In the genus Melita, 29 species with pleonites and urosomites lacking dorsal teeth, urosomite 2 bearing robust dorsal setae, and uropod 3 bearing a single-article outer ramus have been recorded (Momtazi et al. 2014; Krapp-Schickel and Sket 2015; Tomikawa et al. 2018, 2022). Melita panda sp. nov. is easily distinguished from these species by the anterodistal projection of the male gnathopod 1 propodus forming a rounded hood that almost completely covers the dactylus.

Melita panda sp. nov. is morphologically similar to M. koreana and M. nagatai in sharing features such as urosomite 2 with three dorsal robust setae on each side, a head with eyes and incised antennal sinus, maxilla 1 with seven setae on the inner plate and setae on palp article 1, a male gnathopod 1 propodus with a developed anterodistal projection, a male gnathopod 2 with a setaceous subrectangular propodus, pereopods 3 and 4 with short dactylus, and a uropod 3 outer ramus that is 1-articulate. However, M. panda sp. nov. differs from M. koreana and M. nagatai in several distinct features. Compared to M. koreana, M. panda sp. nov. has black-and-white body color (M. koreana is almost all gray), an anterodistal projection of the male gnathopod 1 propodus covering dactylus (M. koreana does not completely cover it), male gnathopod 1 propodus with three and one robust setae on posterior margin and at the base of anterodistal projection, respectively (M. koreana lacks these setae but has a robust seta on palmar corner), and a telson with lateral setae (M. koreana lacks these setae). Compared to M. nagatai, M. panda sp. nov. has a black-and-white body color (M. nagatai is almost all gray), lacks setae at the base of maxilla 1 palp article 1 (M. nagatai has setae present), has an anterodistal projection of the male gnathopod 1 propodus that covers the dactylus (M. nagatai’s projection does not completely cover it), male gnathopod 1 propodus with three and one robust setae on posterior margin and at the base of anterodistal projection, respectively (M. nagatai lacks these setae but has a robust seta on palmar corner), and has a telson with lateral setae (M. nagatai lacks these setae). The close relationship between M. panda sp. nov. and M. koreana + M. nagatai was also supported by the molecular phylogenetic analyses (Fig. 7).

Melita panda sp. nov. shares similarities with M. bingoensis in the shape of mouthparts, male gnathopods 1 and 2, and female pereopod 6 with a slit-like shallow “pocket” at the coxa base. Nonetheless, it differs from M. bingoensis in the following aspects (with M. bingoensis features in parentheses): urosomite 2 with three (M. bingoensis has two) robust setae on each side, anterodistal projection of male gnathopod 1 propodus covering the dactylus (while in M. bingoensis, it does not completely cover it), coxa of female pereopod 6 deeper than wide (in M. bingoensis, it is wider than deep), and telson with lateral setae (which is absent in M. bingoensis). Although, M. bingoensis was not included in our molecular phylogenetic analyses, based on morphological similarities, M. panda sp. nov. is also presumed to be phylogenetically close to M. bingoensis.

Key to species of Melita from Japan

1 Uropod 1 outer ramus 1-articulate 2
– Uropod 1 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 Black-and-white body color; anterodistal projection of male gnathopod 1 propodus fully covering dactylus M. panda sp. nov.
– Almost all gray body color; 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 times width; female coxa 6 wider than deep M. shimizui (Uéno, 1940)
– Male uropod 3 outer ramus longer than 7 times width; female coxa 6 as wide as depth 13
13 Male gnathopod 2 propodus elevated proximally; female gnathopod 2 basis with small palmate setae M. okinawaensis Tomikawa & Nakano, 2022
– Male gnathopod 2 propodus not elevated proximally; 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 M. rylovae Bulyčeva, 1955
– Maxilla 1 palp article 1 with setae; male gnathopod 2 propodus with transverse palmar margin 16
16 Setae on maxilla 1 palp article 1 reaching distal part of palp article 2; pereopods 5–7 with basis not extremely expanded M. hoshinoi Yamato, 1990
– Setae on maxilla 1 palp article 1 not reaching distal part of palp article 2; pereopods 5–7 with basis extremely expanded M. pilopropoda Hirayama, 1987

Conclusion

Melita panda sp. nov. is clearly distinguished from its congeners by morphological and molecular features, indicating that it is an undescribed distinct species. The discovery of this new species sheds light on the high species diversity of Melita in the waters around Japan. Molecular phylogenetic analyses were shown to be useful for inferring phylogenetic relationships among species of the genus and detecting undescribed species.

Acknowledgements

We thank Drs Alan Myers, Azman Abdul Rahim, and Rachael Peart for their critical reading and valuable comments on our manuscript. Thanks are also due to Hiroki Yamada and Genta Teranishi for their help in collecting the samples.

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 partly supported by the Japan Society for the Promotion of Science KAKENHI grants JP21H00919, JP22H01011, JP22K06371, and JP22K06373 to KT.

Author contributions

KT collected samples, analyzed the data, and prepared the manuscript. SY wrote the description and conducted a taxonomic review. HA collected samples and analyzed the data. The manuscript was checked and completed by all authors.

Author ORCIDs

Ko Tomikawa https://orcid.org/0000-0003-1521-9016

Hiroyuki Ariyama https://orcid.org/0000-0001-7312-5187

Data availability

All of the data that support the findings of this study are available in the main text.

References

  • Ariyama H (2022) Guidebook of Gammaridean Amphipoda. Kaibundo, Tokyo, 158 pp. [In Japanese]
  • Bousfield EL (1973) Shallow-water gammaridean Amphipoda of New England. Cornell University Press, Ithaca, New York, 312 pp.
  • Bulyčeva AI (1955) Novye vidy bokoplavov (Amphipoda, Gammaridea) iz Japonskogo Morja. II. [New species of amphipods from the Japan Sea. II.]. Trudy Zoologicheskogo Instituta, Akademija Nauk SSSR 21: 193–207.
  • Folmer O, Black M, Hoeh W, 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.
  • Hirayama A (1978) A new gammaridean Amphipoda, Cottesloe cyclodactyla sp. nov., from Amakusa, south Japan. Publications from the Amakusa Marine Biological Laboratory, Kyushu University 4: 235–243.
  • Hirayama A (1987) Taxonomic studies on the shallow water gammaridean Amphipoda of west Kyushu, Japan. VII. Melitidae, Melphidippidae, Oedicerotidae, Philiantidae and Phoxocephalidae. Publications of the Seto Marine Biological Laboratory 32: 1–62. https://doi.org/10.5134/176135
  • Hoang DT, Chernomor O, von Haeseler A, Minh BQ, Vinh LS (2018) UFBoot2: improving the ultrafast bootstrap approximation. Molecular Biology and Evolution 35: 518–522. https://doi.org/10.1093/molbev/msx281
  • Horton T, Lowry J, De Broyer C, Bellan-Santini D, Copilaş-Ciocianu D, Corbari L, Costello MJ, Daneliya M, Dauvin J-C, Fišer C, Gasca R, Grabowski M, Guerra-García JM, Hendrycks E, Hughes L, Jaume D, Jazdzewski K, Kim Y-H, King R, Krapp-Schickel T, LeCroy S, Lörz A-N, Mamos T, Senna AR, Serejo C, Souza-Filho JF, Tandberg AH, Thomas JD, Thurston M, Vader W, Väinölä R, Valls Domedel G, Vonk R, White K, Zeidler W (2024) World Amphipoda Database Melita Leach, 1814. World Register of Marine Species. http://www.marinespecies.org/aphia.php?p=taxdetails&id=101679 [Accessed on 2024-07-18]
  • Kalyaanamoorthy S, Minh BQ, Wong TKF, von Haeseler A, Jermiin LS (2017) ModelFinder: Fast model selection for accurate phylogenetic estimates. Nature Methods 14: 587–589. https://doi.org/10.1038/nmeth.4285
  • Labay VS (2016) Review of amphipods of the Melita group (Amphipoda: Melitidae) from the coastal waters of Sakhalin Island (Far East of Russia). III. Genera Abludomelita Karaman, 1981 and Melita Leach, 1814. Zootaxa 4156: 1–73. https://doi.org/10.11646/zootaxa.4156.1.1
  • Momtazi F, Sari A, Maghsoudlou A (2014) New species and new record of hadzioids (Amphipoda: Senticaudata, Hadzioidea) from the Persian Gulf, Iran. Zootaxa 3881: 440–452. https://doi.org/10.11646/zootaxa.3881.5.2
  • Morino H (1991) Gammaridean amphipods (Crustacea) from brackish waters of Okinawa Island. Publications of Itako Hydrobiological Station 5: 13–26.
  • Nagata K (1965) Studies on marine gammaridean Amphipoda of the Seto Inland Sea. III. Publications of the Seto Marine Biological Laboratory 13: 291–326. https://doi.org/10.5134/175410
  • Nakamura Y, Nakano T, Ota Y, Tomikawa K (2019) A new species of the genus Elasmopus from Miyako Island, Japan (Crustacea: Amphipoda: Maeridae). Zootaxa 4544: 395–406. https://doi.org/10.11646/zootaxa.4544.3.5
  • Nation JL (1983) A new method using hexamethyldisilazane for preparation of soft insect tissues for scanning electron microscopy. Stain Technology 58: 347–351. https://doi.org/10.3109/10520298309066811
  • Rambaut A, Teslenko M, van der Mark P, Ayres DL, Darling A, Höhna S, Larget B, Liu L, Suchard MA, Huelsenbeck JP (2018) Posterior summarization in Bayesian phylogenetics using Tracer 1.7. Systematic Biology 67: 901–904. https://doi.org/10.1093/sysbio/syy032
  • Ronquist F, Teslenko M, van der Mark P, Ayres DL, Darling A, Höhna S, Larget B, Liu L, Suchard MA, Huelsenbeck JP (2012) MRBAYES 3.2: efficient Bayesian phylogenetic inference and model selection across a large model space. Systematic Biology 61: 539–542. https://doi.org/10.1093/sysbio/sys029
  • Stephensen K (1944) Some Japanese amphipods. Videnskabelige Meddelelser fra Dansk Naturhistorisk Forening I København 108: 25–88.
  • Tomikawa K, Tashiro S, Kobayashi N (2012) First record of Gammarus koreanus (Crustacea, Amphipoda, Gammaroidea) from Japan, based on morphology and 28S rRNA gene sequences. Species Diversity 17: 39–48. https://doi.org/10.12782/sd.17.1.039
  • Tomikawa K, Kobayashi N, Kyono M, Ishimaru S, Grygier MJ (2014a) Description of a new species of Sternomoera (Crustacea: Amphipoda: Pontogeneiidae) from Japan, with an analysis of the phylogenetic relationships among the Japanese species based on the 28S rRNA gene. Zoological Science 31: 475–490. https://doi.org/10.2108/zs140026
  • Tomikawa K, Soh HY, Kobayashi N, Yamaguchi A (2014b) Taxonomic relationship between two Gammarus species, G. nipponensis and G. sobaegensis (Amphipoda: Gammaridae), with description of a new species. Zootaxa 3873: 451–476. https://doi.org/10.11646/zootaxa.3873.5.1
  • Tomikawa K, Sasaki T, Aoyagi M, Nakano T (2022) Taxonomy and phylogeny of the genus Melita (Crustacea: Amphipoda: Melitidae) from the West Pacific islands, with descriptions of four new species. Zoologischer Anzeiger 296: 141–160. https://doi.org/10.1016/j.jcz.2021.12.005
  • Trifinopoulos J, Nguyen LT, von Haeseler A, Minh BQ (2016) W-IQTREE: a fast online phylogenetic tool for maximum likelihood analysis. Nucleic Acids Research 44(W1), W232–W235. https://doi.org/10.1093/nar/gkw256
  • Uéno M (1940) Some freshwater amphipods from Manchoukuo, Corea and Japan. Bulletin of the Biogeographical Society of Japan 10: 63–85.
  • Yamato S (1987) Four intertidal species of the genus Melita (Crustacea: Amphipoda) from Japanese waters, including descriptions of two new species. Publications of the Seto Marine Biological Laboratory 32: 275–302. https://doi.org/10.5134/176142
  • Yamato S (1988) Two species of the genus Melita (Crustacea: Amphipoda) from brackish waters in Japan. Publications of the Seto Marine Biological Laboratory 33: 79–95. https://doi.org/10.5134/176148
  • Yamato S (1990) Two new species of the genus Melita (Crustacea: Amphipoda) from shallow waters of the Seto Inland Sea of Japan. Publications of the Seto Marine Biological Laboratory 34: 149–165. https://doi.org/10.5134/176168
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