Orientomaera incisa Ariyama, 2020

Kim, Jae-Hong Choi and Young-Hyo, 2023, A newly record species Orientomaera incisa (Crustacea, Amphipoda, Maeridae) from East Sea, Korea, Journal of Species Research 12 (4), pp. 294-298 : 295-297

Orientomaera incisa Ariyama, 2020 ( Figs. 2-4 )

Ĥ래ẺŔΘųăNjș (ljḡ)

Orientomaera incisa Ariyama, 2020: 471 , figs. 16 - 20.

Material examined. 6♂ (cat No. NIBRIV0000904520), Keungajaebawi Rock , Dokdo-ri , Ulleung-eup, Ulleung-gun, Gyeongsangbuk-do, Korea, 37°14′50″N, 131°51′ 47.37″E, 13 June 2018 ; 5♂ 5$, Wangdolcho Rock , Hupori , Hupo-myeon, Uljin-gun, Gyeongsangbuk-do, Korea, 36°39′58″N, 129°30′55″E, 14 August 2018 ; 5♂, Neunggeol , Sadong-ri , Ulleung-eup, Ulleung-gun, Gyeongsangbuk-do, Korea, 37°26′55″N, 130°52′30″E, 13 September 2018 ; 3 inds, Jukdo island , Jeodong-ri , Ulleung-eup, Ulleung-gun, Gyeongsangbuk-do, Korea, 37°31′38″N, 130° 55′58″E, 13 September 2018 . The specimens were collected by a SCUBA diving, collected by S.H. Kim.

Description. Adult male, body ( Figs. 2 , 3A) 7.2 mm long (cat No. NIBRIV0000904520), dorsally smooth. Head, eyes black, ovate to reniform, ommatidia compacted; lateral cephalic lobe subrounded, anteroventral corner acute.

Antenna 1 ( Fig. 3B) elongated; peduncular article 1 elongated, with 8 or more robust setae on posterior margin, group of setae on dorsal margin; peduncular article 2 subrectangular and slender; length ratio of peduncular articles 1 - 3 = 1.00: 1.00: 0.38; flagellum 13-articulate, shorter than peduncular articles; accessory flagellum 7-articulate.

Antenna 2 ( Fig. 3C) elongated; peduncular article 3 - 5 with row of setae ventrally; length ratio of peduncular articles 3 - 5 = 1.00: 2.00: 1.87; flagellum 7-articulate.

Gnathopod 1 ( Fig. 3D) subchelate; coxa subquadrate, width subequal in length, anterodistal corner produced acutely; basis subrectangular, with 9 short setae anteriorly, 4 long and 2 short setae posteriorly; ischium with 4 long setae posteriorly; carpus subequal in length to propodus, with group of setae ventrally, oblique row of setae posterodistally; propodus subovate, half of anterodistal margin with a group of long setae, posterior margin with several clusters of long setae; palm oblique, with a row of short setae; dactylus falcate, fitting palm, with accessory setule on dorsal margin.

Gnathopod 2 ( Fig. 3E) large, massive, subchelate; coxa subquadrate, 0.64 times as wide as long; basis subrectangular, narrowed posteroproximally, with small hump anterodistally; carpus subtriangular, with a robust seta anterodistally; propodus subquadrate, 0.78 times as wide as long, with several clusters of setae on both margins; palm trans- verse, middle portion with 2 large triangular processes, palmer margin with two rows of robust setae, palmer corner with two unequal small processes; dactylus falcate, fitting palm, with a setule on anterior margin.

Pereopod 3 ( Fig. 3F), coxa subquadrate, width subequal in length; basis subrectangular, narrowed posteroproximally; merus to dactylus slender, with sparse setae.

Pereopod 4 similar to pereopod 3, except coxa 4 slightly longer than that of pereopod 3.

Pereopod 5 ( Fig. 3G), basis subovate, anterior margin with 4 short setae, posterodistal corner roundly produced; merus subrectangular, moderate, both margins with sparse setae; carpus and propodus slender, subrectangular; dactylus falcate, length 0.40 times as long as propodus.

Pereopod 6 similar to pereopod 5, but slightly longer than pereopod 5.

Pereopod 7 ( Fig. 4A ), basis subovate, anterior margin nearly straight, with a row of 8 short robust setae, posterior margin roundly expanded, with sparse short setae; merus somewhat dilated posteriorly, both margins with unequal setae; carpus and propodus slender, subrectangular, with several clusters of setae anteriorly; dactylus falcate.

Uropod 1 ( Fig. 4B ), peduncle subrectangular, subequal in length to rami, with a row of 3 dorsolateral, 4 dorsomedial, a ventromedial, and a basofacial robust setae; inner ramus subequal to outer one, with 6 dorsal robust setae, 2 subapical robust setae, and a robust seta on apex; outer ramus with 4 dorsal robust setae, 2 subapical slender setae, and a robust seta on apex.

B C D A G E F

Uropod 2 ( Fig. 4C ), peduncle subrectangular, subequal in length to rami, with 2 robust setae on dorsolateral margin; inner ramus subequal to outer one.

Uropod 3 ( Fig. 4D ), peduncle subrectangular, short, length 0.77 times as long as inner ramus; both rami subequal in length, apex covered with group of unequal setae.

Telson ( Fig. 4E ) wider than deep, cleft 90% medially, lateral margins convex, each lobe with 2 setae laterally, distal margins of lobes with 2 processes each, inner process longer than outer process, with a robust seta between processes.

Female (DKUAMP202302), Body length 5.2 mm long, morphologically similar to male in shape, but distinguished from male by having narrow oostegites.

Distribution. Japan, Korea (East Sea).

Remarks. Orientomaera incisa is similar to O. brevispina , however, it can be easily distinguished by the presence of two distinct teeth on the palm of gnathopod 2. According to Ariyama (2020), O. incisa apparently possesses the characters of the genus Orientomaera , except for the shape of the gnathopod 2 palm. Our Korean specimens closely agree with the original description by Ariyama (2020), however, the following morphological differences were found between our material and the original description: 1) antenna 2 less setose; 2) pereopod 3 dactylus more angled.

Figures

Fig. 2. Orientomaera incisa, Ariyama, 2020, adult male, 7.2 mm, habitus. Scale bar=1.0 mm.

Fig. 4. Orientomaera incisa, Ariyama, 2020, adult male, 7.2 mm. A, pereopod 7; B, uropod 1; C, uropod 2; D, uropod 3; E, telson. Scale bars:A =1.0 mm, B-E=0.2 mm.