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.

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.

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).

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.

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.

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.

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.

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

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.

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

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).