Mongoloniscus orientalis Jiang, Li & Huang sp. nov.

Figs 4 G, H, 8

Type material.

Holotype. China: ♂ (20230403006), Heilongjiang Province, Harbin: Xiangfang District, Longrui Residential (126.6821 ° N, 45.7233 ° E), 160 m asl., 3. ix. 2023, coll. Junjie Zong.

Paratypes. 6 ♂♂, 13 ♀♀ (20230403003 – 20230403008), same data as the holotype . China: 2 ♂♂, 2 ♀♀ (20231030301, - 02), Shanxi Province, Taiyuan: Longcheng Forestry Park (37.9228 ° N, 112.7565 ° E), 1610 m asl., 30. x. 2023, coll. Tianyun Chen, Yuan Xiong & Jiabo Fan .

Diagnosis.

Antennal flagellum with distal article as long as proximal article. Pereopod 6 basis fringed with long setae. Pereopod 7 ischium with sternal margin slightly concave and fringed with setae carpus with rounded lamellar lobe on tergal margin. Apex of pleopod 1 exopod bilobed, outer lobe larger than inner one.

Description.

Body length of males 8–12 mm and females 7–16 mm. Body elongated and convex, ~ 2.8 × as long as widest pereonite. Dorsum distinctly granulated, brown-gray color with usual yellowish muscle spots. Numerous gland pores along entire pereonites margin (Fig. 4 G, H). Pereonite 1 with rounded postero-lateral corners, distal margin nearly straight. Noduli laterales on pereonites 1–4 and 7 shifted from lateral margins than those on pereonites 5 and 6. Telson triangular, slightly wider than length, outer margin slightly concave near middle, posterior apex pointed; uropodal exopod ~ 2.8–3.6 × as long as protopod in males and ~ 1.2–2 × in females; protopod with an incision on outer margin (Figs 4 G, H, 8 B).

Cephalon with medial lobe triangular, not surpassing lateral lobes in dorsal view. Eyes with 20 ommatidia. Antenna with fifth article of peduncle longer than flagellum; flagellum with distal article as long as proximal one (Fig. 8 C).

Pereopod 1 bearing a brush of long setae on its carpus and merus (Fig. 8 D). Pereopod 6 basis fringed with long setae (Fig. 8 E). Pereopod 7 ischium with sternal margin slightly concave and fringed with setae, rostral surface with shallow depression; carpus with rounded lamellar lobe on tergal margin (Fig. 8 F).

Pleopods 1–5 exopods with monospiracular internal lungs (Fig. 8 G – K). Male: pleopod 1 exopod drop-like, outer margin sinuous, apex bilobed; outer lobe larger than inner one, inner lobe bearing one seta at apex (Fig. 8 G). Pleopod 2 exopod nearly triangular, bearing one line of setae on outer margin (Fig. 8 H). Pleopod 1 endopod with broad basal part, narrowed towards apex, apex bent outwards and pointed (Fig. 8 G); pleopod 2 endopod longer than exopod, distal article thin and long (Fig. 8 H).

Remarks.

This new species resembles M. koreanus by basis of pereopod 6 having long setae and a distal protrusion on the sternal margin, ischium of pereopod 7 fringed with setae. However, it can be differentiated from the latter by antenna with two equal flagellum articles, and its noduli laterales on pereonites 1–4 and 7 are much farther from lateral margins than those on pereonites 5 and 6. In M. koreanus, the distal article of the flagellum is twice as long as the proximal article, and the noduli laterals are almost at the same distance from the lateral margin. Furthermore, this species together with M. koreanus formed two clearly different clades in the phylogenetic analysis (Fig. 2), whose interspecific distances were much higher than their intraspecies distances (Suppl. material 1: table S 2).

Etymology.

Latin orientalis = east. The new species name refers to its distribution in east China. We suggest the Chinese common name as “ 东方蒙潮虫 ”.

Distribution.

China (Heilongjiang, Shanxi).