Maera denticoxa, Ariyama & Kodama & Tomikawa, 2020

Ariyama, Hiroyuki, Kodama, Masafumi & Tomikawa, Ko, 2020, Species of the Maera-clade collected from Japan. Part 4: addenda to genera Maera Leach, 1814 and Quadrimaera Krapp-Schickel & Ruffo, 2000, with revised keys to Japanese species of the clade (Crustacea: Amphipoda: Maeridae), Zootaxa 4885 (3), pp. 336-352 : 338-344

Maera denticoxa sp. nov.

[Japanese name: Kita-sunnariyokoebi, new]

( Figs 2–7 )

Maera danae .— Tomikawa et al., 2010: table 1, figs 1–3. [not Maera danae ( Stimpson, 1853) ]

Type material. Holotype: male, 14.7 mm (OMNH-Ar-11724), Nagane, Otsuchi Bay in Iwate Prefecture, 39°21'45"N, 141°57'35"E ( Fig. 1B ), 3–4 m depth, under stones, by SCUBA, 18 February 2019, coll. M. Kodama. Paratypes: female, 15.6 mm (OMNH-Ar-11725), same locality, 7–8 m depth, under stones, by SCUBA, 11 July 2018, coll. M. Kodama ; female, 15.5 mm (OMNH-Ar-11734, not dissected), same locality, 7–8 m depth, on coarse sand under stones, by SCUBA, 19 May 2020, coll. M. Kodama ; ovigerous female, 13.2 mm (OMNH-Ar-11726), Nagoshi, Otsuchi Bay in Iwate Prefecture, 39°21'04"N, 141°56'50"E ( Fig. 1B ), 4.3 m depth, by SCUBA and airlift, 14 November 2018, coll. N. Ohtsuchi ; male, 16.2 mm and female, 16.3 mm (OMNH-Ar-11727, 11728), Daikoku Island, Akkeshi Town , Hokkaido, 42°57'47"N, 144°52'19"E ( Fig. 1A ), intertidal, using hand net, fixed by 99% Ethanol, 24 June 2005, coll. K. Tomikawa.

Type locality. Nagane , Otsuchi Bay in Iwate Prefecture, Japan .

Etymology. From the Latin dentatus, -a, -um (= dentate) + coxa, referring to the shapes of coxae 1–6.

Diagnosis. Eyes present. Mandible, palp article 1 with acute distal tooth. Coxae 1–6, posteroventral margins each with 1–7 notches; coxa 1 anteroventral corner acutely produced. Gnathopod 2 in both sexes, palm strongly oblique, defined by small tooth. Pereopods dactyli simple; 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 about 3 times as long as peduncle. Telson longer than wide, distal ends pointed, lateral margins each with 7–8 robust setae.

Description. Based on holotype, male, 14.7 mm (OMNH-Ar-11724).

Head ( Figs 2–3 ). Eyes oval, about 0.2 times length of head. Antenna 1 weakly setose; peduncular articles 1–3 with length ratio of 1: 1.1: 0.3, article 1 with 8 posteromedial robust setae; accessory flagellum with 7 articles; primary flagellum with 29 articles, terminal article minute. Antenna 2 about 0.55 times length of antenna 1, setose; peduncular articles 3–5 with length ratio of 1:3.15:2.3; flagellum with 10 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 12–14 accessory setae; palp article 1 with acute distal tooth, articles 1 – 3 length ratio (excluding distal tooth of article 1) 1: 3.6–3.7: 2.2–2.4, articles 2 – 3 setose. Lower lip with inner lobes, distal margins of inner and outer lobes weakly setose, mandibular processes small. Maxilla 1, inner plate with 3 long and 3 short apical setae, medial margin bearing a few feeble setae, outer plate with 11 apical robust setae and medial feeble setae, palp article 1 with a few laterodistal and lateral 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 2 setae. Maxilliped, inner plate truncate, distal margin with many thick setae, distomedial corner with 4 robust setae ventrally; outer plate with 27 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. 4 ). Gnathopod 1, coxa anteroventral corner acutely produced, ventral margin with 5 small notches posteriorly; basis setose on anteroproximal and posterior margins; carpus swollen posterodistally, posterior margin and medial surface heavily setose; propodus about 80% as long as carpus, anterior and posterior margins setose, palm defined by 3 short robust setae; dactylus slender, slightly curved posteriorly. Gnathopod 2, coxa subquadrate, posteroventral margin with 7 small notches; basis narrow, anteroproximal and posterior margins and anterodistal corner with several setae; merus with acute posterodistal spine; carpus lobate posterodistally, posterior margin heavily setose; propodus slender, length about 1.9 times width, anteromedial surface and posterior margin setose; palm strongly oblique, defined by small triangular tooth with robust seta, palmar margin with 6 minute teeth, bearing 9 lateral and 12 medial robust setae; dactylus strongly curved, anterior margin with 17 setae.

Pereopods 3–4, shapes subequal, pereopod 3 about 1.2 times as long as pereopod 4; coxa trapezoidal, posteroventral margins with 4 and 2 small notches, respectively, gill large, shorter than basis length; basis rectilinear, anterior and posterior margins each with a few long proximal setae and many small robust setae; propodus lined with bundle of robust setae posteriorly; dactylus short, about 0.4 times length of propodus, simple. Pereopods 5–7, shapes subsimilar, about 1.1, 1.5, 1.6 times lengths of pereopod 4, respectively; coxae 5–6, posteroventral corner with single small notch, coxa 7 lacking notch, coxae 6–7 anteroventral margin bearing 3 robust setae; basis rectangular, lengths about 2.0, 1.95, 1.8 times widths respectively, posteroproximal corner roundly projected, anterior margin with many short robust setae, posterior margin serrate, posterodistal corner square; carpus and merus lined with bundle of robust setae; dactylus short, 0.3–0.4 times length of propodus, simple.

Pleon ( Fig. 5 ). Epimera 1–3 acutely projected posteroventrally, each with lateral ridge, ventral margins of epimera 1–3 with 7, 7, 5 robust setae, respectively. Pleopods 1–3 slender, pleopods 2 – 3 shorter than pleopod 1; peduncles with 6 (4 lost), 8 (1 lost), 7 coupling hooks respectively; both rami each with 12–14 articles. Uropod 1, peduncle with large basofacial and distolateral robust setae and 17 dorsolateral and 17 dorsomedial robust setae; outer ramus subequal length of inner ramus, about 0.7 times as long as peduncle, with 4 dorsolateral, 6 dorsomedial and 4 terminal robust setae; inner ramus with 6 dorsolateral, 12 dorsomedial, 1 ventrolateral and 5 terminal robust setae. Uropod 2 short, about 0.55 times length of uropod 1; peduncle laterodistal corner triangularly projected, dorsolateral margin, dorsomedial margin and distomedial corner with 11, 6 and 3 robust setae, respectively; outer ramus about 0.9 times length of inner ramus, almost same length as peduncle, with 8 dorsolateral, 5 dorsomedial and 5 terminal robust setae; inner ramus with 5 dorsolateral, 14 dorsomedial, 1 ventrolateral and 5 terminal robust setae. Uropod 3 long, about 195% as long as uropod 2; peduncle, lateral and medial surfaces with 1 and 8 robust setae, respectively, laterodistal corner bearing 8 robust setae; both rami rectilinear, outer ramus about 1.1 times length of inner ramus, about 3.1 times length of peduncle, with vestigial second article; lateral and medial margins of both rami lined with many robust setae, distal margins bearing several robust setae and a few slender setae, longest seta about 0.2 times length of outer ramus. Telson about 1.15 times longer than wide, each lateral margin with 7 – 8 robust setae, tips acutely projected, dorsal surfaces of each lobe with a robust seta and 3 sensory setae.

Description of female (paratype, 15.6 mm, OMNH-Ar-11725). Gnathopod 2 ( Fig. 5 F-G2) almost same as male, holotype, 14.7 mm (OMNH-Ar-11724) except for oostegite.

Variation. Notches on posteroventral margins of coxae 1 – 6 present in all specimens. Their numbers vary from 1 to 7 ( Table 1 ).

Coloration in life ( Fig. 6 ). Eyes dark brown, other parts pale pink.

Remarks. Maera denticoxa sp. nov. has small notches on the coxae 1 – 6. Only three species having such notches were recorded in the genus ( Ariyama 2020): Maera loveni ( Bruzelius, 1859) [Japanese specimens], M. pachytelson Karaman & Ruffo, 1971 , and M. sagamiensis Ariyama, 2020 . However, the notches are present on the coxa 2, the coxae 1–2 and the coxae 1–3 in these species, respectively. These three species also differ from the new species in the shape of the gnathopod 2 palm, the shape of the telson, and the number of the coupling hooks, respectively.

Habitat. On coarse sand bottom under stones ( Fig. 7 ), intertidal to 8 m depth (present study).

Distribution. Coast of Daikoku Island in Hokkaido and Otsuchi Bay in Iwate Prefecture, Japan (present study).

Figures

FIGURE 1. Map showing collecting sites of the examined specimens.A, Daikoku Island in Akkeshi Town, Hokkaido; B, Otsuchi Bay in Iwate Prefecture; C, north of Tanegashima Island in Kagoshima Prefecture.

FIGURE 2. Maera denticoxa sp. nov. Holotype, male,14.7 mm (OMNH-Ar-11724). Habitus.

FIGURE 3. Maera denticoxa sp. nov. Holotype, male, 14.7 mm (OMNH-Ar-11724). Scales: 0.1 mm.

FIGURE 4. Maera denticoxa sp. nov. Holotype, male, 14.7 mm (OMNH-Ar-11724). Scales: 0.2 mm.

FIGURE 5. Maera denticoxa sp. nov. All but F, holotype, male, 14.7 mm (OMNH-Ar-11724); F, paratype, female, 15.6 mm (OMNH-Ar-11725). Scales: 0.2 mm.

FIGURE 6. Maera denticoxa sp. nov. Holotype, male, 14.7 mm (OMNH-Ar-11724). Live specimen, photograph by M. Kodama.

FIGURE 7. Maera denticoxa sp. nov. In situ photograph of paratype, female, 15.5 mm (OMNH-Ar-11734) by M. Kodama.