A new species of Leipsuropus Stebbing, 1899 (Amphipoda: Podoceridae) from Japan Author Matsumoto, Yu Graduate School of Science, Hokkaido University. Sapporo 060 - 0810, Japan Author Kajihara, Hiroshi Faculty of Science, Hokkaido University. Sapporo 060 - 0810, Japan E-mail: kakui @ eis. hokudai. ac. jp & DA Author Kakui, Keiichi Faculty of Science, Hokkaido University. Sapporo 060 - 0810, Japan E-mail: kakui @ eis. hokudai. ac. jp & DA text Nauplius 2023 e 2023005 2023-02-20 31 1 8 http://dx.doi.org/10.1590/2358-2936e2023005 journal article 10.1590/2358-2936e2023005 2358-2936 10716750 D4641240-C79E-471D-8F7C-8A2DA4AA04A8 Leipsuropus seisuiae sp. nov. ( Figs. 2–6 ) Zoobank: urn:lsid:zoobank.org:act: 0F13E56C-CDA3-4514-95CC-09F621D1DBA8 Figure 1. Map showing the sampling site. A , B , map showing the sampling site in Japan and the Kumano Sea. Maps were generated by using GMT6 ( A , Wessel et al., 2019 ) or based on GSI Maps ( B , https://maps.gsi.go.jp). Figure 2. Photograph of lateral view of Leipsuropus seisuiae sp. nov. , male, holotype, ethanol fixed specimen. Scale bar: 1 mm. Type material. Holotype : male, 3.4 mm , ICHUM6353 ; TR/ V “Seisui-maru”, Stn. 1, Kumano Sea , Northwestern Pacific ( 34°06.92’N 136°42.73’E to 34°04.98’N 136°42.25’E), 340– 338 m depth , biological dredge, 7 November 2017 , Y. Matsumoto and K. Kakui coll. Diagnosis (male). Pereonites 2–5 each with five narrow spiniform projections on tergal plate. Pereonites 6 and 7 segmented. Telson with dorsal tubercle. Gnathopod-2 palm with small, proximal, denticulate projection. Description of holotype . Body( Figs.2 , 3A–C , 6D ) 3.4 mm long, depressed. Head with mid-dorsal spiniform projection, pair of dorsolateral spiniform projections, and pair of ventral projections at insertion of antenna 2. Pereonite 1 with 2 mid-dorsal spiniform projections and pair of lateral spiniform projections.Pereonites2–7 segmented, each with mid-dorsal spiniform projection, pair of dorsolateral spiniform projections, and pair of lateral spiniform projections. Pleonites 1–2 each with mid-dorsal spiniform projection and pair of dorsolateral projections.Pleonite3 without projection. Urosomites 1–3without projection;urosomite1 with posterodorsal simple seta. Telson ( Figs. 3B , 6D ) linguiform, with dorsal tubercle bearing dorsal simple seta. Antenna 1 ( Fig. 4A ) with peduncular article 1 having ventral setulose setae and dorsal bifurcate setae; other parts lost. Antenna 2 ( Fig. 4B ) with peduncular articles 1–2 (fused) having distolateral projection and antennal gland cone directed ventrodistally; peduncular article 3 with ventral setulose setae and dorsal bifurcate setae; other parts lost. Upper lip ( Fig. 4C ; partly broken) ventrally setulated, with ventral hollow. Epistome ( Fig. 4D ) produced anteriorly. Mandibles ( Fig. 4E, E 1, F, F1 ) with incisor bearing 5 cusps; lacinia mobilis with 3 cusps; subdistal region with 3 (left) or 2 (right) accessory blades and 3 (left) or 1 (right) plumose seta; molar with plate-like structure bearing pectinate margin. Palp with naked article 1; article 2 with medial setulose setae; article 3 distally expanded, with setulose setae in distal half. Lower lip ( Fig. 4G ) with developed inner lobes and mandibular processes; distal region of inner and outer lobes covered with thin setae. Maxilla 1 ( Fig. 4H ) with vestigial inner plate; outer plate with 8 distal robust setae (6 bifurcate, 2 simple). Palp with naked article 1; article 2 with 7 distal robust setae (1 broken, 3 serrate, 3 simple), ventral simple seta, and 3 dorsal setulose setae.Maxilla 2 ( Fig. 4I ) with inner and outer plates having distal setulose setae and covered with thin setae. Maxillipeds ( Fig. 4J, J 1 ) with inner plate bearing 6 distal setulose setae and 3 distal short robust setae; outer plate with 4 distal setulose setae and 5 medial robust setae and several medial simple setae. Palp with4 articles; article 1 naked; article 2with distal and medial setulose setae; articles 3–4 with setulose setae on almost all surfaces. Gnathopod 1 ( Figs. 3A , 5A, A 1 ) subchelate. Coxa with slight lateral projection. Basis with 1 anterior and 1 posterodistal simple setae. Ischium with posterodistal setulose setae. Merus with posterior setulose setae. Carpus with 1 medial and several posterior setulose setae. Propodus with setulose setae on almost all margins; palmar margin slightly concave, with proximomedial 4 robust setulose setae. Dactylus slightly curved posteriorly, with 2 posterosubdistal denticles. Gnathopod 2 ( Figs. 3C , 5B, B 1 ) subchelate. Coxa with lateral projection. Basis with 1 mid-posterior and 3 posterodistal simple setae and lateral anterodistal spiniform projection. Ischium with 2 posterodistal simple setae. Merus with 5 posterodistal simple setae and posterodistal spiniform projection. Carpus short, with simple setae on antero- and posterodistal corners. Propodus ovate, with simple setae on almost all margins; palmar margin with proximal small denticulate projection, proximal bifurcate robust seta, mid-plumose seta, and 11 robust setae. Dactylus curved posteriorly. Figure 3. Leipsuropus seisuiae sp. nov. , male, holotype. A , Body, lateral view, pleopods omitted; B , posterior portion of body, lateral view, body, pereopods omitted; C , head, pereon, and pleonites 1–2, dorsal view. Scale bar: 1 mm. Figure 4. Leipsuropus seisuiae sp. nov. , male, holotype. A , Peduncular article 1 of right antenna 1, lateral view; B , peduncular articles 1–3 (articles 1, 2 fused) of right antenna 2, lateral view; C , upper lip, anterior view; D , epistome, lateral view; E , F , left and right mandibles, medial views; E1, F1 , distal portion of left and right mandibles, medial views; G , lower lip, ventral view; H , right maxilla 1, ventral view (arrowhead, inner plate); I , left maxilla 2, dorsal view; J , left maxilliped, dorsal view; J1 , outer and inner plates of right maxilliped (some setae of inner plate omitted). Scale bars: A, B, E–G, 0.1 mm; C, D, H–J, E1, F1, J1, 0.05 mm. Figure 5. Leipsuropus seisuiae sp. nov. , male, holotype. A , Left gnathopod 1, lateral view (robust setulose setae on palm omitted); A1 , palm and dactylus of left gnathopod 1, medial view (setulose setae omitted); B , left gnathopod 2, lateral view (medial setae omitted); B1 , distal part of left gnathopod 2, medial view (lateral setae omitted); C–G , left pereopods 3–7, lateral view. Scale bars: 0.1 mm. Figure 6. Leipsuropus seisuiae sp. nov. , male, holotype. A–C , Left (A, B) or right (C) pleopods 1–3, posterior views; D , urosome, telson, and uropods 1 and 3, dorsal view; E , left uropod 3, lateral view. Scale bars: A–D, 0.1 mm; E, 0.05 mm. Pereopod 3 ( Figs. 3A, C , 5C ) 2.33 mm long, with length ratio of basis, ischium, merus, carpus, and propodus 1.00:0.24:0.64:1.01:1.37 (tip of dactylus broken). Coxa pointed laterally. Basis with anterior and posterior simple setae.Ischium with posterodistal simple seta. Merus with posterior simple setae, mid-anterior thick seta and anterodistal bifurcate thick seta. Carpus with anterior, posterior, and distal simple setae and mid-anterior, anterodistal, and posterodistal thick setae. Propodus with anterior simple setae and anterior, posterior, and distal thick setae. Dactylus slightly curved, with 2 anterior simple setae and mid-anterior plumose seta. Pereopod 4 ( Figs. 3A , 5D ) 2.32 mm long, with length ratio of articles from basis to propodus 1.00:0.25:0.73:1.16:1.50 (tip of dactylus broken). Similar to pereopod 3 except: basis with lateral anterodistal spiniform projection; dactylus without anterior simple setae. Pereopod 5 ( Figs. 3A , 5E ) 2.34 mm long, with length ratio of articles from basis to dactylus 1.00:0.27:0.61:1.30:1.65:1.08. Similar to pereopod 4. Pereopod 6 ( Figs. 3A , 5F ) 2.45 mm long, with length ratio of articles from basis to dactylus 1.00:0.27:0.68:1.23:1.63:1.05. Similar to pereopod 5. Pereopod 7 ( Figs. 3A , 5G ) 2.57 mm long, with length ratio of articles from basis to dactylus 1.00:0.28:0.68:1.22:1.65:1.13. Similar to pereopod 6. Pleopods 1–3( Fig. 6A–C ) 0.66 mm , 0.80 mm , 0.76 mm long, respectively. Peduncle with 4 mediodistal coupling hooks. Each segment of both rami bearing 1–3 plumose setae. Uropod 1 ( Fig. 6D ) biramous. Peduncle with 1 distolateral and 2 mediodistal robust setae. Inner ramus with 3 lateral, 3 medial and 4 distal robust setae. Outer ramus with 2 lateral, 1 medial, and 2 distal robust setae. Uropod 3 ( Fig. 6D, E ) curled, with distal thin setae and 3 dorsal simple setae. Etymology. The specific name is a noun in the genitive case and derived from TR/ V “Seisui-maru”, the vessel from which the type specimen was collected. Type locality. Kumano Sea , Japan , Northwestern Pacific ( 34°06.92’N 136°42.73’E to 34°04.98’N 136°42.25’E), 340– 338 m depth . Distribution. So far known only from the type locality. Remarks. Leipsuropus seisuiae sp. nov. is the fifth named species in Leipsuropus . Pereonites 2–7 of male L. seisuiae sp. nov. each has five projections on the tergal plate: one dorsal, a pair of dorsolateral, and a pair of lateral projections. This condition was also found in male L. hongi , but L. seisuiae sp. nov. is distinguished from L. hongi by: i) dorsal projection on the pereonites is narrow and spiniform (broad, keel-like in L. hongi ), ii) gnathopod-2 palmar margin has one small,proximal, denticulate projection (one wide and two large triangular projections in L. hongi ), and iii) the telson has a dorsal tubercle (no tubercle in L. hongi ) ( Ariyama, 2012 ).Differences among congeners including L. seisuiae sp. nov. in a combination of five character states are presented in Tab. 1. A key to world Leipsuropus males is given below.