Austromaera ariakensis, Ariyama, 2019

Ariyama, Hiroyuki, 2019, Species of the Maera - clade collected from Japan. Part 2: genera Austromaera Lowry & Springthorpe, 2005 and Quadrimaera Krapp-Schickel & Ruffo, 2000 (Crustacea: Amphipoda: Maeridae), Zootaxa 4554 (2), pp. 460-496 : 462-466

Austromaera ariakensis sp. nov.

[Japanese name: Ariake-sunnariyokoebi, new]

( Figs 2–5 )

Type material. Holotype: male, 10.3 mm (OMNH-Ar-10591), Ariake Sea , north of Amakusa-kamishima Island in Kumamoto Prefecture, 32°31'11"N 130°20'02"E ( Fig. 1H ), 15 m depth, sandy mud bottom, using Smith-McIntyre grab, 12 May 2006, coll. K. Mori. Paratypes: ovigerous female, 9.3 mm (OMNH-Ar-10592), same data as holotype; female, 7.2 mm (OMNH-Ar-10593), Ariake Sea , off Shimabara City in Nagasaki Prefecture, 32°49'01"N 130°23'04"E ( Fig. 1F ), 26 m depth, using Smith-McIntyre grab, 18 September 2005, coll. K. Mori ; ovigerous female, 10.2 mm (OMNH-Ar-10594), Ariake Sea , off Minami-shimabara City in Nagasaki Prefecture, 32°39'01"N 130°23'01"E ( Fig. 1G ), 50 m depth, sandy bottom, using Smith-McIntyre grab, 12 May 2006, coll. K. Mori ; male, 10.0 mm (OMNH-Ar-10595) and female, 9.9 mm (OMNH-Ar-10596), Ariake Sea , northwest of Ōyano Island in Kumamoto Prefecture, 32°37'01"N 130°23'01"E ( Fig. 1G ), 58 m depth, sandy bottom, using Smith-McIntyre grab, 15 May 2006, coll. K. Mori.

Type locality. Ariake Sea , north of Amakusa-kamishima Island in Kumamoto Prefecture, Japan .

Etymology. Referring to the type locality.

Diagnosis. Head, anteroventral slit absent. Gnathopod 1, coxa with anteroventral corner acutely produced, ventral margin with a few posterior notches; propodus posterior margin smooth with a few robust setae. Gnathopod 2 in both sexes, basis anterodistal corner with bundle of setae; merus with small posterodistal spine; propodus posterior margin almost smooth, with several marginal and medial robust setae. Pleonal epimeron 3 strongly projected posteroventrally, posterior margin with a few small teeth. Uropod 3 rami about 2.2 times as long as peduncle. Telson, both lobes each with 2–3 subdistal robust setae.

Description. Based on holotype, male, 10.3 mm (OMNH-Ar-10591), and paratype, ovigerous female, 10.2 mm (OMNH-Ar-10594) for head and pereopod 6.

Head ( Figs 2–3 ). Anteroventral corner minutely produced, slit absent. Eyes about 0.2 times as long as head. Antenna 1 about half length of body, poorly setose; peduncle with ratio of lengths of articles 1–3 1:1.2:0.2, article 1 with posteromedial robust seta distally; accessory flagellum with 6 articles, terminal article minute, length about 0.2 times primary flagellum; primary flagellum with 36 articles, terminal article minute. Antenna 2 shorter than antenna 1, weakly setose, with ratio of lengths of peduncular articles 3–5 1:3.0:2.4; flagellum damaged. Upper lip, ventral margin rounded, with short setae. Mandible, incisor bearing 4 and 3 cusps on left and right sides, respectively, each lacinia mobilis 3-dentate, with 11 and 9 accessory setae on left and right sides, respectively; palp articles 1 – 3 length ratio 1:2.1:1.8, articles 2 – 3 setose. Lower lip with inner lobes, distal margins of inner and outer lobes bearing many short setae, mandibular processes small. Maxilla 1, inner plate with 3 long apical setae and several feeble medial setae; outer plate with 11 apical robust setae; palp article 1 bearing several lateral setae, article 2 with many apical setae. Maxilla 2, outer plate larger than inner plate; both plates bearing many apical setae, medial margin of inner plate with single seta and many feeble setae. Maxilliped, inner plate truncate, distally setose, distomedial corner with 3 robust setae ventrally; outer plate with 25 long-to-short robust setae on distomedial margin; palp 4-articulate, article 2 setose ventrally, article 3 with many distal setae, article 4 with large apical robust seta.

Pereon ( Fig. 4 ). Gnathopod 1, coxa with anteroventral corner produced acutely, ventral margin with 3 posterior notches and several short setae; basis setose on anterior and posterior margins; carpus subtriangular, anterior and posterior margins and mediodistal surface heavily setose; propodus about 0.85 times as long as carpus, anterodistal corner and anterior margin bearing many long setae, posterior margin smooth, setose, with 4 robust setae medially; dactylus slender, long, almost straight. Gnathopod 2, coxa subquadrate, ventral margin with 3 robust setae and several short setae; basis relatively narrow, about 2.9 times as long as width, anterodistal corner with bundle of setae, posterior margin setose; merus with small posterodistal spine; carpus triangular, posterodistal corner slightly produced, posterior margin heavily setose; propodus about 1.5 times as long as carpus, length about 1.95 times width, anterodistal corner bearing many long setae, posterior margin almost smooth, setose, with 5 marginal and 5 medial robust setae; dactylus slender, slightly curved distally, anterior margin with single seta proximally.

Pereopods 3–4 subequal in shape, pereopod 3 about 1.1 times length of pereopod 4; coxae subquadrate, ventral margins with several short setae, gills large, subequal to bases lengths; bases rectilinear, anteroproximal margins with several long setae, posterior margins bearing many long setae. Pereopod 5 about 1.2 times length of pereopod 4; coxa with quadrate posteroventral corner, anteroventral margin and medial surface each with robust seta; basis subovate, length about 2.0 times width, anterior margin with 6 short and 1 long robust setae, posterior margin minutely serrate, with short setae. Pereopod 6, coxa with quadrate posteroventral corner, gill small, about half length of basis; basis subovate, length about 1.9 times width, anterior margin with 5 short and 1 long robust setae, posterior margin minutely serrate, with short setae. Pereopod 7 about 1.2 times length of pereopod 5; coxa trapezoidal; basis subovate, length about 1.5 times width, anterior margin with 8 short and 1 long robust setae, posterior margin weakly serrate, each tooth with short seta.

Pleon ( Fig. 5 ). Epimera 1–2 slightly projected posteroventrally, ventral margins bare, epimeron 2 with oblique lateral ridge; epimeron 3 strongly projected posteroventrally, posterior margin with 3 small teeth distally, ventral margin lacking setae. Pleopods 1–2 longer than pleopod 3; peduncle of pleopod 3 wider than those of pleopods 1– 2, bearing several setae; both rami subequal in all pleopods, with 12–13 articles. Uropod 1, peduncle with 6 dorsolateral, 6 dorsomedial and 1 distolateral robust setae; outer ramus about 0.9 times length of inner ramus, about 0.8 times as long as peduncle, with 2 lateral and 4 terminal robust setae; inner ramus with 4 lateral, 5 medial and 2? terminal robust setae. Uropod 2 about 0.6 times length of uropod 1; peduncle bearing 2 dorsolateral robust setae, distolateral and distomedial corners each with 3 robust setae; outer ramus about 0.8 times length of inner ramus, slightly longer than peduncle, with 2 lateral and 4 terminal robust setae; inner ramus with 3 lateral, 6 medial and 3 terminal robust setae, dorsomedial margin pectinate. Uropod 3 about 1.25 times as long as uropod 2; peduncle, lateral and medial margins and distolateral corner with 1, 2, 4 robust setae, respectively; rami subequal in length, about 2.2 times as long as peduncle, distal margins minutely incised, each with 1 long and 1–2 short setae, longest seta about 0.1 times length of rami; outer ramus bearing 5 groups and single robust setae laterally and 4 robust setae medially, without vestigial second article; inner ramus with 4 lateral and 7 medial robust setae. Telson about 1.65 times longer than wide, narrowed distally, ventral surface and right lateral margin bearing 2 and 1 short robust setae, respectively; tips pointed, each with 2 subdistal robust setae, longest robust seta about 0.2 times as long as telson.

Variation. Ovigerous female, paratype, 10.2 mm (OMNH-Ar-10594). Gnathopod 2 ( Fig. 5 F-G2) subsimilar to that of holotype, male, but propodus wider and shorter, length about 1.9 times width, posterior margin bearing 4 robust setae. Telson, left lobe with 3 subdistal robust setae. Small female, paratype, 7.2 mm (OMNH-Ar-10593). Gnathopod 2 ( Fig. 5 SF-G2) almost similar to that of holotype, but posterior margin of propodus with 2 marginal and 4 medial robust setae. Telson, right lobe with 3 subdistal robust setae.

Coloration. Unknown.

Remarks. Austromaera ariakensis sp. nov. can be distinguished from its congeners by the acutely produced coxa 1, the merus of gnathopod 2 with a small posterodistal spine and the telson lobes each with 2–3 subdistal robust setae. Austromaera brevicaudata has a rounded anteroventral corner of the coxa 1 ( Ledoyer 1984, Krapp- Schickel 2009), and both A. bruzelii and A. mastersii have a distinct posterodistal spine on the merus of gnathopod 2 ( Stebbing 1888, Lowry & Springthorpe 2005).

Habitat. Sandy or sandy mud bottom, 15–58 m depth.

Distribution. Japan: Ariake Sea (present study).

Figures

FIGURE 1. Map showing collecting sites of the examined specimens. A, Otsuchi Town in Iwate Prefecture; B, Miura City in Kanagawa Prefecture; C, Maizuru City in Kyoto Prefecture; D, Misaki Town in Osaka Prefecture and Wakayama City in Wakayama Prefecture; E, Kushimoto Town in Wakayama Prefecture; F–H, Ariake Sea; I, Nakadōri Island in the Gotō Islands, Nagasaki Prefecture; J, south of Yakushima Island in Kagoshima Prefecture.

FIGURE 2. Austromaera ariakensis sp. nov. Paratype, ovigerous female, 10.2 mm (OMNH-Ar-10594). Habitus.

FIGURE 3. Austromaera ariakensis sp. nov. Holotype, male, 10.3 mm (OMNH-Ar-10591). Scales: 0.15 mm.

FIGURE 4. Austromaera ariakensis sp. nov. All except for F, holotype, male, 10.3 mm (OMNH-Ar-10591); F, paratype, ovigerous female, 10.2 mm (OMNH-Ar-10594). Scales: 0.3 mm.

FIGURE 5. Austromaera ariakensis sp. nov. All except for F and SF, holotype, male, 10.3 mm (OMNH-Ar-10591); F, paratype, ovigerous female, 10.2 mm (OMNH-Ar-10594); SF, paratype, female, 7.2 mm (OMNH-Ar-10593). Scales: 0.2 mm.