Mongoloniscus polyacanthum Jiang, Li & Huang, 2024

Jiang, Chao, Zhong, Jing, Wang, Zhidong, Li, Weichun & Huang, Luqi, 2024, Taxonomic study on the genus Mongoloniscus Verhoeff, 1930 (Isopoda, Agnaridae) from China: morphological and phylogenetic analyses, ZooKeys 1202, pp. 229-253 : 229-253

Mongoloniscus polyacanthum Jiang, Li & Huang sp. nov.

Figs 4 C, D , 6

Type material.

Holotype. China: ♂ ( 20210908003 ), Liaoning Province, Chaoyang, Fenghuangshan National Forestry Park (41.54725 ° N, 120.4743 ° E), 210 m asl., 8. iv. 2021, coll. Chao Jiang.

Paratypes. 1 ♂, 8 ♀♀ ( 20210908001 , 20210908002 , 20210908004 – 20210908010 ) same data as the holotype .

Diagnosis.

Antennal flagellum with distal article ~ 1.2 × as long as proximal article. Pereopod 7 ischium sternal margin fringed sparse setae. Pleopod 1 exopod with one line of setae on inner margin, distal apex deeply bilobed, inner lobe as long as outer one, but slightly wider than outer lobe.

Description.

Body length of males 7–9 mm and females 8–11 mm. Body elongated and convex, ~ 2–2.5 × as long as widest pereonite. Dorsum distinctly granulated, brown-gray in color with usual yellowish muscle spots. Numerous gland pores along entire pereonites margin. Pereonite 1 with rounded postero-lateral corner, posterior margin nearly straight. Noduli laterales on pereonites 1–4 much farther from lateral margins than those on pereonites 5–7. Telson triangular, with slightly concave on lateral margins, posterior apex pointed; uropodal exopod ~ 1.5–2 × as long as protopod; protopod with an incision on the outer margin (Figs 4 C, D , 6 B ).

Cephalon with medial lobe triangular, not surpassing the lateral lobes in dorsal view (Fig. 6 A ). Eyes with 20 ommatidia. Antenna with fifth article of peduncle longer than flagellum; flagellum with distal article 1.2 × as long as proximal one (Fig. 6 C ).

Pereopod 1 bearing a brush of long setae on its carpus and merus (Fig. 6 D ). Pereopod 7 ischium rostral surface with a shallow depression; carpus not expanded on the tergal margin (Fig. 6 F ).

Pleopods 1–5 exopods with monospiracular internal lungs (Fig. 6 G – K ). Male: pleopod 1 exopod oval, apex deeply bilobed, inner lobe as long as outer one, but slightly wider than outer lobe; outer margin sinuous, bearing one seta near middle and apex, respectively; inner margin with one line of setae; (Fig. 6 G ). Pleopod 2 exopod almost triangular, bearing one line of setae on the outer margin. Pleopod 1 endopod with broad basal part, narrowed towards apex, apex acute and bent outwards, bearing several setae (Fig. 6 G ); pleopod 2 endopod longer than exopod, distal article thin and long (Fig. 6 H ).

Remarks.

This new species is similar to M. sinensis in the large body size, noduli laterales arrangement, and the fringed sparse setae on the pereopod 6 basis and pereopod 7 ischium. However, it can be distinguished from the latter by the distal article of the antennal flagellum longer than the proximal article, carpus of pereopod 7 without a rounded lobe on the tergal margin, and pleopod 1 exopod inner margin bearing a line of well-developed setae. In M. sinensis , the antennal flagellum articles are equal in length, the carpus of pereopod 7 has a rounded lobe on the tergal margin, and the pleopod 1 exopod bearing 2–4 setae on the apex of the inner lobe. Furthermore, this species together with M. sinensis formed two clades with high support in the phylogenetic analysis (Fig. 2 ), whose interspecific distances were much higher than their intraspecies distances (Suppl. material 1: table S 2).

Etymology.

Latin prefix poly - = many, plus acanthum = spinous. The new species name refers to the setae on the inner margin of pleopod 1 exopod. We suggest the Chinese common name as “ 多刺蒙潮虫 ”.

Distribution.

China (Liaoning).

Figures

Figure 2. Maximum likelihood phylogenetic tree based on combined COI and 28 S data for Mongoloniscus. Values above the branches represent the posterior probability (PP) and bootstrap support (BS), BS < 70 % or PP < 0.9 are indicated as hyphens.

Figure 4. Habitus of Mongoloniscus species A, C, E, G male, holotype B, D, F, H female, paratype A, B M. crenatus sp. nov. C, D M. polyacanthum sp. nov. E, F M. parvus sp. nov. G, H M. orientalis sp. nov. The blue circles show the noduli laterales arrangement. Scale bars: 3 mm.

Figure 6. Mongoloniscus polyacanthum sp. nov., holotype A cephalon and pereonite 1 in dorsal view B pleonites, telson, and uropod in dorsal view C second antenna D pereopod 1 E pereopod 6 F pereopod 7 G pleopod 1 H pleopod 2 I – K pleopods 3–5 exopods. The abrupt tip of pleopod 2 endopod are indicated as dotted lines. Scale bars: 1 mm (A – F); 0.5 mm (G – K).