Meximaera mooreana ( Myers, 1989 )

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 : 465-470

Meximaera mooreana ( Myers, 1989)

[Japanese name: Kawari-sunnariyokoebi, new]

( Figs 11–15 )

Maera species B Barnard, 1970: 159, fig.100.— Barnard, 1971: 85, figs 31, 38, 40–41.

Maera mooreana Myers, 1989: 72 , figs 9–10.— Appadoo, Myers & Fagoonee, 2002: 661 , figs 12–13.— Ren, 2012: 244, fig. 106.

Meximaera mooreana .— Krapp-Schickel, 2008a: 22.

Material examined. Male, 4.3 mm (OMNH-Ar-10626), Tagurazaki coast, Wakayama City, Wakayama Prefecture, 34°16ʹ02ʹʹN 135°03ʹ39ʹʹE ( Fig. 1B ), uppermost subtidal, under stones, 10 April 2005, coll. H. Ariyama; ovigerous female, 5.5 mm (OMNH-Ar-10627), same locality and habitat, 17 June 2007, coll. H. Ariyama ; male, 6.5 mm (OMNH-Ar-10628), same locality and habitat, 30 June 2007, coll. H. Ariyama ; male, 5.2 mm (OMNH-Ar-10629) and male, 3.4 mm (OMNH-Ar-10630), same locality and habitat, 9 April 2016, coll. H. Ariyama.

Type locality. Moorea in the Society Islands, French Polynesia ( Myers 1989) .

Diagnosis. Eyes situated anteriorly. Mandible, palp article 1 with acute distal tooth. Gnathopod 1, coxa anteroventral corner roundly produced. Gnathopod 2 in male, basis wide, palm moderately oblique, defined by small tooth, palmar margin with rounded excavation. Gnathopod 2 in female, basis slender, propodus rectangular, palm weakly oblique, lacking excavation. Pereopods dactyli simple; bases of pereopods 5–7 subrectangular, narrowed distally, posterodistal corners square. Pleonal e pimera 1–3 each with small tooth posteroventrally. Uropod 3 very long, rami subequal, about 3.4 times length of peduncle. Telson longer than wide, longest distal seta about 0.3 times length of telson.

Description. Based on male, 6.5 mm (OMNH-Ar-10628), male, 5.2 mm (OMNH-Ar-10629) for antennae and telson, and ovigerous female, 5.5 mm (OMNH-Ar-10627) for habitus.

Head ( Figs 11–12 ). Eyes about 0.15 times as long as head, situated anteriorly. Antenna 1 about 0.55 times body length, poorly setose; peduncle slender, ratio of lengths of articles 1–3 1:1.25:0.5, article 1 with 4 robust setae posteromedially, anterodistal corner with bundle of setae; accessory flagellum with 6 articles, terminal article minute, length about half length of primary flagellum; primary flagellum with 12 articles, terminal article minute. Antenna 2 about 0.6 times length of antenna 1, weakly setose; peduncle slender, ratio of lengths of articles 3–5 1:2.35:1.9; flagellum with 7 articles, terminal article minute. Upper lip, ventral margin rounded, with dense short setae. Mandible, molar developed; each incisor bearing 3 cusps, each lacinia mobilis 4-dentate, number of accessory setae 5 on both sides; palp article 1 with acute distal tooth, articles 1 – 3 length ratio (excluding distal tooth of article 1) 1:1.8:1.6, articles 2 – 3 setose. Lower lip with inner lobes, distal margins of both lobes setose, mandibular processes small. Maxilla 1, inner plate bullet-shaped, with 3 long and 2 tiny apical setae, medial margin bare; distal margin of outer plate with 8 robust setae; palp 2-articulate, setose apically. Maxilla 2, outer plate larger than inner plate; both plates bearing many apical setae, medial margin of inner plate with 3 feeble setae. Maxilliped, inner plate truncate, distally setose, distomedial corner with 2 robust setae; outer plate with 16 long-to-short robust setae on distomedial margin; palp with 4 articles, article 2 setose medially, article 4 with large apical robust seta.

Pereon ( Fig. 13 ). Gnathopod 1, coxa lozenge-shaped, anteroventral corner produced roundly; basis with posterior margin bearing many long setae; carpus about 1.3 time as long as propodus, broadened distally, posterior margin and medial surface heavily setose; propodus palm defined by 2 short robust setae; dactylus slender, curved posteriorly, anterior margin with single seta. Gnathopod 2, coxa subtrapezoidal, produced posteroproximally; basis wide, about 1.9 times as long as width, poorly setose; merus with acute posterodistal spine; propodus about 2.4 times length of carpus, rectangular, length 1.8 times width; palm moderately oblique, defined by small triangular tooth, palmar margin with rounded excavation in middle and 7 lateral and 7 medial robust setae, posterior margin proximal to tooth also bearing single medial robust seta; dactylus stout, curved distally.

Pereopods 3–4, shapes subequal, pereopod 3 about 1.1 times length of pereopod 4; coxae subquadrate, gills on coxae 3–4 small and large, respectively; bases rectilinear, poorly setose. Pereopods 5–7, shapes subsimilar, lengths about 1.15, 1.5, 1.55 times of pereopod 4, respectively; coxae 5–7 bearing 1, 3, 2 robust setae, respectively; bases subrectangular, narrowed distally, lengths about 2.55, 2.2, 1.9 times widths respectively, posteroproximal corners roundly projected, anterior margins with several short robust setae, posterior margins minutely serrate, posterodistal corners square; dactyli straight.

Pleon ( Fig. 14 ). Epimera 1–3 each with small tooth on posteroventral corner; ventral margins of epimera 2–3 with 4 and 5 robust setae, respectively. Pleopods 1–3, pleopod 3 shortest; peduncles each with 2 coupling hooks, peduncle of uropod 3 bearing distal robust seta; each inner and outer ramus with 6 and 8 articles, respectively. Uropod 1, peduncle with 4 ventrolateral, 9 dorsolateral, 6 dorsomedial and 1 large distolateral robust setae; outer ramus slightly longer than inner ramus, about 0.7 times length of peduncle, with 4 lateral, 2 medial and 3 terminal robust setae; inner ramus with 4 lateral, 4 medial and 5 terminal robust setae. Uropod 2 about 0.6 times length of uropod 1; peduncle bearing 1 dorsolateral and 4 dorsomedial robust setae; rami subequal, outer ramus almost same length as peduncle, with 3 lateral, 2 medial and 4 terminal robust setae; inner ramus with 3 lateral, 4 medial and 4 terminal robust setae. Uropod 3 very long, about 2.25 times length of uropod 2, rectilinear; distolateral corner and medial margin of peduncle with 1 and 3 robust setae, respectively; rami subequal, about 3.4 times length of peduncle; outer ramus with minute second article, lateral margin of outer ramus setose, medial margin of outer ramus and lateral margin of inner ramus bearing many short robust setae, medial margin of inner ramus with 8 robust setae, distal margins of both rami with several short setae laterally, longest seta about 0.1 times length of outer ramus. Telson about 1.25 times longer than wide, lateral margins bare, dorsal surfaces of each lobe with 2 sensory setae distally, distal margins of lobes each with 2 processes (inner processes smaller than outer), bearing 2 robust setae and sensory seta, longest robust seta about 0.3 times length of telson.

Description of female. Ovigerous female, 5.5 mm (OMNH-Ar-10627). Gnathopod 2 ( Fig. 14 F-G2), basis slen- der, about 3.8 times as long as width, posterior margin with 4 long setae in middle; propodus about 1.7 times length of carpus, rectangular, length twice width; palm weakly oblique, lacking excavation, defining tooth indistinct, palmar margin with 7 small lateral robust setae and 7 (6 small and 1 large) medial robust setae.

Variation. Small male, 3.4 mm (OMNH-Ar-10630). Gnathopod 2 ( Fig. 14 SM-G2), propodus narrower, length twice width; palmar excavation indistinct, palmar margin with 4 small lateral robust setae and 6 (5 small and 1 large) medial robust setae.

Coloration in life ( Fig. 15 ). Eyes dark brown, article 1 of antenna 2 and mouth parts pale orange, other parts white.

Remarks. Morphological characters of the present specimens closely resemble those in the literature ( Barnard 1970, Myers 1989, Appadoo et al. 2002, Ren 2012). However, one character is different from Myers (1989) and Appadoo et al. (2002): the mandibular palp article 1 is acutely projected in the specimens, whereas that is not projected in the two papers [ Ren’s (2012) figure indicates a presence of the projection]. Because presence or absence of the projection is one of the important characters dividing genera of the Maera -clade ( Krapp-Schickel 2008a), closer examination is needed in all of the Meximaera species.

Habitat. Among coral and algae ( Myers 1989), among algae ( Appadoo et al. 2002), coral reef ( Ren 2012), under stones (present study); intertidal and shallow-subtidal ( Appadoo et al. 2002).

Distribution. Pacific Ocean: Society Islands ( Myers 1989), Hawaii ( Barnard 1970, 1971). China: Hainan Island ( Ren 2012). Japan: Wakayama Prefecture (present study). Indian Ocean: Mauritius ( Appadoo et al. 2002).

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 11. Meximaera mooreana (Myers, 1989). Ovigerous female, 5.5 mm (OMNH-Ar-10627). Habitus, pereopod 7 lost.

FIGURE 12. Meximaera mooreana (Myers, 1989). All but M, male, 6.5 mm (OMNH-Ar-10628); M, male, 5.2 mm (OMNH- Ar-10629). Scales: 0.05 mm.

FIGURE 13. Meximaera mooreana (Myers, 1989). Male, 6.5 mm (OMNH-Ar-10628). Scales: 0.1 mm.

FIGURE 14. Meximaera mooreana (Myers, 1989). All except for F, M and SM, male, 6.5 mm (OMNH-Ar-10628); F, ovigerous female, 5.5 mm (OMNH-Ar-10627); M, male, 5.2 mm (OMNH-Ar-10629); SM, male, 3.4 mm (OMNH-Ar-10630). Scales: 0.1 mm.

FIGURE 15. Meximaera mooreana (Myers, 1989). Male, 5.2 mm (OMNH-Ar-10629). Live specimen, photograph by H. Ariyama.