Exalloniscus triangulus Li & Jiang, 2024

Jiang, Chao, Yao, Chonghui, Huang, Luqi & Li, Weichun, 2024, Five new species of Exalloniscus Stebbing, 1911 (Crustacea, Isopoda, Oniscidea) from China, Zoosystematics and Evolution 100 (2), pp. 373-383 : 373

Exalloniscus triangulus Li & Jiang sp. nov.

Figs 1E , 5

Type material.

Holotype. China: male, Hubei Province, Jingshan County, Kongshandong Scenic Area (30°58'N, 113°02'E), alt. 100 m, 9 April 2021, Zhidong Wang and Tianyun Chen leg., habitus no. KSD2302, prep. slide no. L23097 (JXAUM).

Diagnosis.

Male pleopod 1 exopod distinctly convex on outer margin, and endopod with a triangular lobe and a seta recurved inwards at apical part.

Description.

Length 2.9 mm.

Body oval, flattened and white mixed with pale brown. Cephalon with lateral lobes slightly protruding laterally, apex rounded. Eyes with three ommatidia. Pereonites 1 with postero-lateral corner nearly right-angled, pereonites 2-7 with postero-lateral corners directed backwards. Pleonites 3-5 with epimera falciform, protruding backwards. Telson triangular, twice as wide as long, lateral margin gently concave, ending with rounded apex. Uropod exopod almost as long as endopod (Fig. 1E ).

Antenna with fifth article of peduncle longer than flagellum; ratio of flagellum approximately 3:2:2 (Fig. 5A ).

Pereopod 1 with long strong setae on sternal margin of merus and carpus, carpus with transversal antennal grooming brush (Fig. 5B ). Pereopod 7 with several strong setae on sternal margin; basis with distinct water conducting system; ischium slightly convex on sternal margin (Fig. 5C ).

Male pleopod 1 exopod basal half broad, distal half narrowed towards blunted apex, distinctly convex on outer margin; endopod ending with triangular lobe and seta recurved inwards (Fig. 5D ). Pleopod 2 exopod triangular with several setae on outer margin; endopod flagelliform, longer than exopod (Fig. 5E ). Pleopods 3 and 4 exopods almost oval, pleopod 5 triangular with several setae on outer margin (Fig. 5F-H ).

Etymology.

Latin: Exalloniscus triangulus = triangular. The new species name refers to the male pleopod 1 endopod ending with a triangular lobe.

Remarks.

This new species is similar to E. malaccensis Taiti & Ferrara, 1988 in having a triangular lobe at the apical part of male pleopod 1 endopod. But it can be distinguished by pleopod 1 exopod distinctly convex on the outer margin, and the apical part of endopod with a triangular lobe and a seta recurved inwards (Fig. 5D ). In E. malaccensis , pleopod 1 exopod is distinctly concave on the outer margin, and the apical lobe of endopod is thinner and recurved outwards ( Taiti and Ferrara 1988: fig. 23D).

Figures

Figure 1. Habitus of Exalloniscus species. A. E. duospinatus sp. nov., holotype; B (holotype); C (paratype). E. curvispinatus sp. nov.; D. E. thailandensis, male; E. E. triangulus sp. nov., holotype; F. E. tridentatus sp. nov., holotype; G. E. cortii, male; H. E. taitii sp. nov., holotype. Scale bar: 1 mm.

Figure 5. Exalloniscus triangulus sp. nov., holotype. A. Antenna; B. Pereopod 1; C. Pereopod 7; D. Pleopod 1; E. Pleopod 2; F. Pleopod 3 exopod; G. Pleopod 4 exopod; H. Pleopod 5 exopod. Scale bar: 0.1 mm.