Quadrimaera angulata, 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 : 345-350

Quadrimaera angulata sp. nov.

[Japanese name: Maru-sunnariyokoebi, new]

( Figs 8–11 )

Type material. Holotype: female, 10.1 mm (OMNH-Ar-11729), north of Tanegashima Island in Kagoshima Prefecture, 30°54.07'N, 131°02.32'E – 30°54.65'N, 131°01.97'E ( Fig. 1C ), 140–152 m depth, using beam trawl, 29 May 2006, coll. K. Tomikawa. Paratypes: females, 9.2 and 6.6 mm (OMNH-Ar-11730, 11731), same data as holotype.

Type locality. North of Tanegashima Island in Kagoshima Prefecture, Japan .

Etymology. From the Latin angulatus, -a, -um (=angular, angulate), referring to the shape of the pereopod 7 basis.

Diagnosis. Mandible, palp article 1 with distal tooth. Gnathopod 1, coxa anteroventral corner pointed. Female gnathopod 2, anterior margin of basis without robust setae, anterodistal corners of basis and ischium lobate on lateral and medial surfaces, propodus subrectangular, palm slightly oblique and rounded, defined by small tooth, palmar margin with small rounded excavation in middle, posterior excavation absent. Pereopods 5–7, bases subovate, posterodistal corners roundly lobate in pereopods 5–6 and angular in pereopod 7, posterior margins not setose. Uropod 3, outer ramus longer than inner ramus, about 1.7 times length of peduncle. Telson longer than wide, tips of both lobes incised, each with 2 robust setae, longest robust seta about 0.8 times as long as telson.

Description. Based on holotype, female, 10.1 mm (OMNH-Ar-11729) and paratype, female, 9.2 mm (OMNHAr-11730) for lower lip.

Head ( Figs 8–9 ). Anteroventral corner produced acutely, eyes subrounded, about 0.2 times as long as head. Antenna 1 slender, poorly setose; peduncular articles 1–3 with length ratio of 1: 1.15: 0.25, article 1 with 4 robust setae posteriorly; accessory flagellum long, with>12 articles, tip lost; primary flagellum with>28 articles, tip lost. Antenna 2 about 35% length of body, poorly setose; peduncular articles 3–5 with length ratio of 1: 2.9: 2.65; flagellum with 8 articles, terminal article minute. Upper lip, ventral margin rounded, with short setae. Mandible, incisor bearing 5 cusps and 8 accessory setae, left lacinia mobilis 4-dentate, right lacinia mobilis 5-dentate; palp article 1 with distal tooth, articles 1–3 length ratio (excluding distal tooth of article 1) 1: 2.05: 1.7 in left and 1: 2.25: 1.75 in right, articles 2 – 3 setose. Lower lip with inner lobes, distal margins weakly setose, distal parts of outer lobes each with bundle of setae and dense fine setae, mandibular processes small. Maxilla 1, inner plate bullet-shaped, apically with long plumose seta and several short setae, medial margin bare; distal margin of outer plate with 7 robust setae; palp article 2 with many apical setae. Maxilla 2, outer plate larger than inner plate; medial margin of inner plate with several distal setae and several feeble setae. Maxilliped, distomedial corner of inner plate with 3 distal and 2 ventral robust setae; outer plate with 19 long-to-short robust setae on distomedial margin; palp with 4 articles, article 4 with large apical robust seta.

Pereon ( Fig. 10 ). Gnathopod 1, coxa anteroventral corner pointed; basis with many long setae on posterior margin and medial surface; carpus with shallow excavation on anterior margin; propodus about 85% length of carpus, palm defined by 5 short robust setae. Gnathopod 2, coxa subquadrate; basis relatively narrow, anterodistal corners on lateral and medial surfaces lobate, anterior margin with several minute setae, posterior margin bearing several long setae; ischium, anterodistal corners on lateral and medial surfaces lobate; merus with acute posterodistal spine; propodus subrectangular, slightly widened distally, length about 1.35 times width; palm slightly oblique, rounded, defined by small tooth with small robust seta, margin with small rounded excavation in middle, posterior excavation absent, anterior lobe with 5 lateral and 4 medial robust setae, posterior lobe bearing 8 lateral and 8 medial robust setae; dactylus, inner margin slightly curved.

Pereopods 3–4 subequal in shape, pereopod 3 about 1.1 times length of pereopod 4; coxa subrectangular; basis with posterior margin bearing several long setae. Pereopod 5 about 1.2 times length of pereopod 4; coxa with posterior lobe bearing robust seta; basis oblong, length about 2.0 times width, posterodistal lobe rounded, anterior margin with 6 short robust setae; merus swollen in middle. Pereopod 6 about 135% length of pereopod 5; coxa with 2 and 1 ventral robust setae on anterior and posterior lobes, respectively; basis subovate, length about 1.65 times width, posterodistal lobe rounded, anterior margin with 6 short robust setae, posterior margin minutely serrate. Pereopod 7 about 0.9 times length of pereopod 6; coxa subtrapezoidal, anteroventral corner with robust seta; basis subovate, length about 1.5 times width, posterodistal lobe angular, anterior margin with 6 short robust setae, posterior margin minutely serrate.

Pleon ( Fig. 11 ). Epimera 1–3 slightly projected posteroventrally; epimera 1–2 each with oblique lateral ridge, ventral margins of epimera 1–3 with 2, 3, 5 robust setae, respectively. Pleopods 1–3, inner rami each with 10 articles and outer rami with 14, 13, 12 articles respectively; pleopod 3 shortest, peduncle bearing 3 robust setae distally. Uropod 1, peduncle with 1 basofacial, 11 dorsolateral, 10 dorsomedial and 1 distolateral robust setae; outer ramus about 85% length of inner ramus, about 75% length of peduncle, with 4 lateral, 6 medial and 5 (1 lost) terminal robust setae; inner ramus with 8 lateral, 9 medial and 5 terminal robust setae. Uropod 2 about 0.7 times length of uropod 1; peduncle bearing 5 dorsolateral and 3 dorsomedial robust setae; outer ramus about 85% length of inner ramus, about 115% length of peduncle, with 8 lateral, 3 medial and 5 (1 lost) terminal robust setae; inner ramus with 5 lateral, 8 medial and 5 terminal robust setae. Uropod 3 about 0.9 times length of uropod 2; distolateral and distomedial corners of peduncle with 2 and 3 robust setae, respectively; outer ramus about 1.1 times length of inner ramus, about 1.7 times length of peduncle; outer ramus with single and 3 groups of robust setae laterally and 5 robust setae medially, distal margin with minute second article and 10 setae; inner ramus with 1+1+2 robust setae laterally and 4 robust setae medially, distal margin with 7 setae. Telson longer than wide, each lateral margin with 2 sensory setae subdistally; distal margins of lobes each with 2 processes, 1 sensory seta and 2 long robust setae, longest robust seta about 0.8 times length of telson.

Coloration in life. Unknown.

Remarks. This new species has a distal tooth on the mandibular palp article 1, although Ariyama (2019) diagnosed the lack of the tooth in the genus Quadrimaera . As a result of reexamining all literature on the genus, the following five species are revealed to possess the distal tooth: Q. frater Myers, 2014 from the Chagos Archipelago; Q. kaiulani ( Barnard, 1970) from Hawaii; Q. massavensis ( Kossmann, 1880) from the Red Sea ( Krapp-Schickel & Ruffo 2006); Q. micheli Appadoo, Myers & Fagoonee, 2002 sensu Hughes (2015) from Cocos Islands (another species different from the true Q. micheli ); and Q. vietnamica Dang & Le, 2011 from Vietnam. Quadrimaera angulata sp. nov. and these species resemble one another and share some characters (e.g. slightly oblique and rounded palm of the gnathopod 2 and incised lobes of the telson). However, this new species can be distinguished from the other five species by the shape of the pereopod 7 basis and the longer rami of the uropod 3 ( Table 2 ).

Habitat. Bottom material unknown, 140–152 m depth. The examined specimens were collected together with Quadrimaera quadrimana ( Dana, 1853) [two males, 5.4 and 4.8 mm (OMNH-Ar-11732, 11733)].

Distribution. North of Tanegashima Island in Kagoshima 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 8. Quadrimaera angulata sp. nov. Holotype, female, 10.1 mm (OMNH-Ar-11729). Habitus.

FIGURE 9. Quadrimaera angulata sp. nov. All but F, holotype, female, 10.1 mm (OMNH-Ar-11729); F, paratype, female, 9.2 mm (OMNH-Ar-11730). Scales: 0.1 mm.

FIGURE 10. Quadrimaera angulata sp. nov. Holotype, female, 10.1 mm (OMNH-Ar-11729). Scales: 0.2 mm.

FIGURE 11. Quadrimaera angulata sp. nov. Holotype, female, 10.1 mm (OMNH-Ar-11729). Scales: 0.2 mm.