Metopelloides lowryi, Ariyama & Moritaki, 2023

Ariyama, Hiroyuki & Moritaki, Takeya, 2023, Two New Amphipods Associated with a Hermit Crab from the Kumano-nada, Central Japan (Crustacea: Amphipoda: Isaeidae, Stenothoidae), Records of the Australian Museum (Rec. Aust. Mus.) 75 (4), pp. 357-370 : 358-359

Metopelloides lowryi sp. nov.

urn:lsid:zoobank.org:act:EAA1BF45-028A-4079-A33C-B5CA8FC5777F

[Japanese name: Yadokari-tatesokoebi, new]

Figs 1–5

Holotype: OMNH-Ar-12498 (TAMBL-CR 1775), male, 4.3 mm, Kumano-nada, off Owase City, Mie Prefecture, 34°01'22.0"N 136°20'57.6"E, 190–350 m depth, associated with Propagurus obtusifrons (Ortmann, 1892) ( Paguridae ), coll. T. Moritaki, 13 October 2016.

Type locality. Kumano-nada, off Owase City in Mie Prefecture, Japan.

Etymology. The species name is dedicated to the late Dr James K. Lowry for his great contribution to amphipod taxonomy.

Diagnosis. Antenna 1 short, peduncular article 2 0.3 times length of article 1. Gnathopod 1 small, posterior margin of dactylus bare. Gnathopod 2 stout, anterior margin of basis with several setae, palm oblique. Telson without robust setae.

Description (based on holotype, male, 4.3 mm). Body ( Fig. 1 ) oval. Coxa 1 small, perfectly hidden by coxa 2; coxae 2, 3 large, coxa 4 extremely large; coxae 5–7 small, perfectly hidden by coxa 4.

Head ( Figs 1 , 2 ). Rostrum small. Ocular lobes rounded. Eyes large (diameter: ca. 0.4 times head length). Antenna 1 short, ca. 0.25 times BL; peduncular articles 1–3 with length ratio of 1.0:0.3:0.25, article 1 stout, lacking setae; accessory flagellum vestigial, with 3 minute setae on tip; primary flagellum with 6 articles, article 2 short, articles 3–5 each bearing aesthetasc posterodistally. Antenna 2 longer than antenna 1 (ca. 1.55 times), slender, sparsely setose; peduncular articles 3–5 with length ratio of 1.0:2.0:1.7, anteromedial surfaces with 4, 4, 2 robust setae, respectively; flagellum with 13 articles, terminal article narrow. Upper lip asymmetrical, ventral margin hollowed. Mandibles, incisors wide, with 9–10 distal denticles; laciniae mobilis broad, left one fan-shaped, with 11 denticles, right one rectangular, composed of 4 quadrate blades; accessory blades 9 in left, 11 in right; palpi relatively short, slender (length ca. 4.7 times width), with 3 setae. Lower lip, outer plate with mandibular lobe, mediodistal corner with 3 short setae. Maxilla 1 with small inner plate bearing single short seta; outer plate with 7 robust setae apically, medial margin bearing several feeble setae; tip of palp acutely projected, with long robust seta, medial margin lined with 5 robust setae. Maxilla 2, inner plate triangular, tip with several setae; outer plate longer, rounded and setose distally. Maxilliped enlarged; distal margins of inner plates each bearing 3 short setae; distomedial lobe of outer plate short and narrow, tip with short robust seta, lateral margin bearing many feeble setae; palp stout, articles 1–3 wide, medial margins each with several robust setae, article 4 falcate, medial margin bearing many feeble setae.

Pereon ( Fig. 3 ). Gnathopod 1 small; basis straight, anterior margin and posterodistal corner with 3 and 1 setae, respectively; merus setose distally; carpus moderately elongate, anterodistal corner and posterior margin setose; propodus subequal to carpus in length, palm strongly oblique, defined by 2 lateral and 2 medial robust setae; dactylus almost straight. Gnathopod 2 stout; basis straight, anterior margin lined with several evenly-spaced setae, posterodistal corner setose; ischium, posterodistal corner setose; merus rounded distally, posterior margin with several setae; carpus with posterior lobe setose distally; propodus broad, ca. 2.65 times length of carpus, anterodistal corner setose, palm oblique, defined by acute projection, distal half of palm convex and serrated, with several robust setae, proximal half concave; dactylus slightly curved posteriorly. Pereopod 3 slender, longer than gnathopod 2; basis–carpus sparsely setose; propodus ca. 1.45 times length of carpus, slightly widened distally, distal and posterior margins with 2+3+3+3 and 2+2+1+1 robust setae, respectively; dactylus narrow. Pereopod 4 slender, similar to pereopod 3; propodus, distal and posterior margins with 2+3+3+3 and 3+2+1 robust setae, respectively. Pereopod 5 shorter than pereopod 4; basis straight, anterior margin lined with several robust setae; merus, anterior and posterior margins and carpus, anterior margin each with several robust setae; propodus slightly widened distally, distal and anterior margins with 2+3+3 and 3+3+1 robust setae, respectively. Pereopod 6 slightly shorter than pereopod 5; basis straight, posterodistal corner slightly swollen, anterior margin lined with several robust setae; merus, anterior and posterior margins each with several robust setae; carpus, anterior margin and posterodistal corner bearing several and a few robust setae, respectively; propodus slightly widened distally, distal and anterior margins with 2+3+3 and 3+3+1+1 robust setae, respectively. Pereopod 7 subequal to pereopod 6 in length; basis straight, wider than that of pereopod 6, posterodistal corner weakly swollen, anterior margin lined with several robust setae; merus, anterodistal corner and posterior margin with a few and several robust setae, respectively; carpus, anterior margin and posterodistal corner bearing several and a few robust setae, respectively; propodus slightly widened distally, distal and anterior margins with 2+3+3 and 3+3+2 robust setae, respectively.

Pleon ( Fig. 4 ). Epimeral plates 1–3, posterodistal corners strongly, moderately, and weakly produced, respectively; ventral margins bare. Pleopods slender, pleopod 3 shortest; pleopods 1–3, peduncles with 7, 10, 1 simple setae, respectively, outer rami longer than inner rami, former with 12, 11, 10 and latter with 8, 8, 7 articles, respectively. Uropod 1 long; peduncle with 9 dorsolateral and 4 dorsomedial robust setae; rami shorter than peduncle, outer ramus shorter than inner ramus, with 3 dorsal robust setae, inner ramus bearing 2 dorsal robust setae. Uropod 2 ca. 0.75 times length of uropod 1, peduncle with 5 dorsolateral and 1 dorsomedial robust setae; outer ramus ca. 0.85 times length of peduncle, with 2 dorsal robust setae; inner ramus subequal to peduncle in length, bearing 2 dorsal robust setae. Uropod 3 ca. 0.65 times length of uropod 2, peduncle with 2 dorsodistal robust setae; single ramus 2-articulate, article 1 with 2 dorsodistal robust setae, article 2 slightly longer than article 1, tip acute. Telson ca. 2.05 times longer than broad, bare.

Colour in life ( Fig. 5 ). Eyes light red. Body white with light orange bands on pereonites 1–3, 4, 6–7, coxae 2–4 (anterior part) and coxa 4 (posterior part). This coloration resembles that of the hermit crab (see Fig. 11 ) and is probably useful for camouflage.

Remarks. Metopelloides lowryi sp. nov. is characterized by: (1) a short article 2 of antenna 1 (0.3 times length of article 1); (2) a slender mandibular palp with 3 setae (length ca. 4.7 times width); and (3) an oblique palm of gnathopod 2. No other congeners have this combination of characters. Although M. lowryi has a similar gnathopod 2 to M. micropalpa , this new species can be distinguished by the short article 2 of antenna 1 (0.6 times length of article 1 in M. micropalpa ).

Habitat. Bottom sediment unknown, 190–350 m depth, associated with Propagurus obtusifrons .

Distribution. Japan: Kumano-nada (present study).

Figures

Figure 1. Metopelloides lowryi sp. nov., holotype male, 4.3 mm, OMNH-Ar-12498, habitus.

Figure 2. Metopelloides lowryi sp. nov., holotype male, 4.3 mm, OMNH-Ar-12498. Scale bars = 0.04 mm.

Figure 3. Metopelloides lowryi sp. nov., holotype male, 4.3 mm, OMNH-Ar-12498. Scale bars = 0.1 mm.

Figure 4. Metopelloides lowryi sp. nov., holotype male, 4.3 mm, OMNH-Ar-12498. Scale bars = 0.1 mm.

Figure 5. Metopelloides lowryi sp. nov., holotype male, 4.3 mm, OMNH-Ar-12498, photographed immediately after fixation, T.Moritaki.

Figure 11. Isaea concinnoides sp. nov., paratype male, ca. 5.6 mm, OMNH-Ar-12500, photographed in aquarium, T. Moritaki.