Maera sagamiensis, Ariyama, 2020

Ariyama, Hiroyuki, 2020, Species of the Maera - clade collected from Japan. Part 3: genera Maera Leach, 1814, Meximaera Barnard, 1969 and Orientomaera Ariyama, 2018 (addendum), with a key to Japanese species of the clade (Crustacea: Amphipoda: Maeridae), Zootaxa 4743 (4), pp. 451-479 : 459-460

Maera sagamiensis sp. nov.

[Japanese name: Sagami-sunnariyokoebi, new]

( Figs 6–10 )

Type material. Holotype: male, 10.1 mm (OMNH-Ar-10625), Sagami Bay, off Jôgashima Island in Miura City , Kanagawa Prefecture, 35°08’31”N 139°32’28”E ( Fig. 1A ), 133–274 m depth, using dredge, 12 February 2015, coll. H. Kohtsuka.

Type locality. Sagami Bay , off Jōgashima Island in Miura City, Kanagawa Prefecture, Japan .

Etymology. Referring to the type locality.

Diagnosis. Eyes present. Mandible, palp article 1 with acute distal tooth. Gnathopod 1, coxa anteroventral corner acutely produced, posteroventral margin with 3 notches. Gnathopod 2 in male, coxa posteroventral margin with 3 notches, palm strongly oblique, defined by acute tooth. Pereopods dactyli simple; coxa 3 posteroventral margin bearing 2 notches posteroventrally, bases of pereopods 5–7 rectangular, posterodistal corners square. Pleonal e pimera 1–3 acutely projected posteroventrally. Uropod 3, outer ramus longer than inner ramus, rami 2.2–2.5 times as long as peduncle. Telson longer than wide, distal ends pointed.

Description. Based on holotype, male, 10.1 mm (OMNH-Ar-10625).

Head ( Figs 6–7 ). Eyes oval, about 0.2 times length of head. Antenna 1 poorly setose; peduncle with ratio of lengths of articles 1–3 1:1.15:0.3, article 1 with 4 small posteromedial robust setae; accessory flagellum with 7 articles, terminal article minute; primary flagellum damaged. Antenna 2 about 0.35 times length of body; peduncle weakly setose posteriorly, with ratio of lengths of articles 3–5 1:3.7:2.5; flagellum setose, with 9 articles, terminal article minute. Upper lip, ventral margin rounded, weakly setose. Mandible, incisor bearing 5 and 4 cusps in left and right, respectively, each lacinia mobilis 4-dentate, with 9 accessory setae; palp article 1 with acute distal tooth, articles 1 – 3 length ratio (excluding distal tooth of article 1) 1:2.5:1.5, articles 2 – 3 setose. Lower lip with inner lobes, distal margins and ventral surfaces of both lobes weakly setose, mandibular processes small. Maxilla 1, inner plate with 3 long and 1 short apical setae, medial and lateral margins and ventral surface bearing feeble setae, outer plate with 10 apical robust setae and medial and ventral feeble setae, palp article 1 with several laterodistal setae, article 2 bearing many apical setae. Maxilla 2, outer plate larger than inner plate; both plates bearing many apical setae, medial margin of inner plate with 1 normal and many feeble setae. Maxilliped, inner plate truncate, distally setose, distomedial corner with 4 robust setae ventrally; outer plate with 23 long-to-short robust setae on distomedial margin; palp 4-articulate, article 2 setose medioventrally, article 3 with many distolateral setae, article 4 with large apical robust seta.

Pereon ( Fig. 8 ). Gnathopod 1, coxa anteroventral corner acutely produced, ventral margin with 3 small notches posteriorly; basis setose on posterior margin; carpus swollen posterodistally, posterior margin and medial surface heavily setose; propodus about 90% as long as carpus, anterior and posterior margins setose, palmar margin bearing many small robust setae medially; dactylus slender, almost straight, anterior margin with single seta. Gnathopod 2, coxa subquadrate, posteroventral margin with 3 small notches; basis relatively narrow, about 2.9 times as long as width, posterior margin with several setae; merus with acute posterodistal spine; carpus swollen posterodistally, posterior margin setose; propodus slender, length about 1.95 times width, anteromedial surface and posterior margin setose; palm strongly oblique, defined by acute tooth, palmar margin with 5 small teeth, bearing 9 lateral and 13 medial robust setae; dactylus curved distally, anterior margin with 10 setae.

Pereopods 3–4, shapes subequal; coxae trapezoidal, coxa 3 with 2 small notches posteroventrally, gills large, subequal to bases lengths; bases rectilinear, anterior and posterior margins each with a few long setae proximally; dactylus of pereopod 4 slender, simple. Pereopods 5–7, shapes subsimilar, pereopods 5, 7 about 1.2, 1.6 times length of pereopod 4, respectively; coxae 6–7, anteroventral margins each with single robust seta; bases rectangular, lengths about 2.9, 2.6, 2.2 times widths respectively, posteroproximal corners roundly projected, anterior margins with many short robust setae, posterior margins serrate, posterodistal corners square; dactyli short, simple.

Pleon ( Fig. 9 ). Epimera 1–3 acutely projected posteroventrally, each with lateral ridge, ventral margins with 3, 2, 5 (1 lost) robust setae respectively. Pleopods 1–3, pleopod 3 shortest; peduncles with 2, 2, 4 coupling hooks respectively; both rami each with 7–9 articles. Uropod 1, peduncle with 15 dorsolateral and 11 dorsomedial robust setae, bearing large distolateral robust seta; outer ramus subequal length to inner ramus, about 0.75 times as long as peduncle, with 4 dorsolateral, 4 dorsomedial and 4 terminal robust setae; inner ramus with 9 dorsomedial and 4 terminal robust setae. Uropod 2 about 0.6 times length of uropod 1; peduncle laterodistal corner projected, dorsolateral margin, dorsomedial margin and distomedial corner with 11, 6 and 3 robust setae, respectively; outer ramus about 0.85 times length of inner ramus, about 95% length of peduncle, with 8 dorsomedial and 3? terminal robust setae; inner ramus with 4 lateral, 9 dorsomedial and 5 terminal robust setae. Uropod 3 long, about 175% as long as uropod 2; peduncle, lateral, medial and ventral margins with 3, 1 and 2 robust setae, respectively, mediodistal corner bearing 4 robust setae; both rami rectilinear, outer ramus about 115% length of inner ramus, about 2.5 times length of peduncle, with vestigial second article; lateral and medial margins of both rami lined with robust setae, distal margins bearing several setae, longest seta about 0.15 times length of outer ramus. Telson about 1.25 times longer than wide, each lateral margin with 4 small robust setae, tips acutely projected, dorsal surfaces of each lobe with a robust seta and 3 sensory setae.

Coloration in life ( Fig. 10 ). Eyes black and white, mouth parts orange, other parts faint orange; yellow internal organs seen through.

Remarks. The presence of small notches on the coxae 1–3 is a distinct character in the genus, although Japanese specimens of Maera loveni and M. pachytelson from France and Israel have minute notches on the coxa 2 and the coxae 1–2, respectively ( Fig. 4-G 2 , G. Karaman & Ruffo 1971). Maera sagamiensis sp. nov. can be distinguished from M. loveni by the shape of the gnathopod 2 palm, and from M. pachytelson by the shape of the telson.

Habitat. Bottom sediment unknown, 133–274 m depth (present study).

Distribution. Sagami Bay in Japan (present study).

Figures

FIGURE 1. Map showing collecting sites of the examined specimens. A, Sagami Bay, off Jōgashima Island in Miura City, Kanagawa Prefecture; B, Tagurazaki coast, Wakayama City in Wakayama Prefecture; C, Sea of Japan, north of Masuda City in Yamaguchi Prefecture.

FIGURE 2. Maera loveni (Bruzelius, 1859). Male, 58.3 mm (OMNH-Ar-10623). Habitus.

FIGURE 4. Maera loveni (Bruzelius, 1859). Male, 58.3 mm (OMNH-Ar-10623). Scales: 0.7 mm.

FIGURE 6. Maera sagamiensis sp. nov. Holotype, male, 10.1 mm (OMNH-Ar-10625). Habitus.

FIGURE 7. Maera sagamiensis sp. nov. Holotype, male, 10.1 mm (OMNH-Ar-10625). Scales: 0.15 mm.

FIGURE 8. Maera sagamiensis sp. nov. Holotype, male, 10.1 mm (OMNH-Ar-10625). Scales: 0.1 mm.

FIGURE 9. Maera sagamiensis sp. nov. Holotype, male, 10.1 mm (OMNH-Ar-10625). Scales: 0.2 mm.

FIGURE 10. Maera sagamiensis sp. nov. Holotype, male, 10.1 mm (OMNH-Ar-10625). Live specimen, photograph by H. Kohtsuka.