Mongoloniscus chevronus Yang & An 2021, sp. nov.
Creators: name: Yang, Lina
name: An, Jianmei
Publisher: name: Zenodo
Year: 2021
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Isopoda
Agnaridae
Mongoloniscus
Mongoloniscus chevronus

description: Mongoloniscus chevronus sp. nov.
Figs 1−3
urn:lsid:zoobank.org:act: AC2B8A03-3DB4-4271-A953-1DD04F308BA8
Material examined. Holotype ♂ (IOA19080601), Benxi City, Liaoning Province, China, 41˚13’51” N, 125˚18’57” E, 6 August 2019, coll. Jianmei An. Allotype ♀ (IOA19080602), same data as holotype. Paratypes 3♂, 5♀ (IOA 19080603, 19080604, 19080605, 19080606, 19080607, 19080608, 19080609, 19080610), same data as holotype.
Diagnosis. Cephalon with well-developed rounded lateral lobes and triangular median lobes (Fig. 1A). Epimera of all pereonites with concave-convex-concave posterior margin (Figs 1A, 3B). Pleon without any patterns (Figs 1A, 3B). For male, carpus of pereopod 7 with convex dorsal margin (Figs 2G, 3I), exopod of pleopod 1 deep hollow at apex, endopod straight with triangular apical part slightly bent outwards (Figs 1E, F, 3D, E).
Description. Holotype ♂ (IOA19080601) length 9.60 mm, maximum width 4.41 mm. Body color blackish brown, surface slightly granulated (Figs 1A, 3B).
Cephalon (Fig. 1A) with well-developed triangular median process and pair of rounded lateral lobes, vertex with faint tubercles and many pale irregular patterns, posterior margin straight.
Antennula (Figs 1B, 3G) with first segment big and cylindrical, second segment rather short and square. Antenna (Figs 1C, 3C) surpassing posterior margin of pereonite 2 but not reaching the posterior margin of pereonite 3; first three segments square; fourth segment 1.8 times as long as third; fifth segment 1.3 times as long as fourth; fourth peduncular segment with one pale bar; fifth peduncular segment with 1–2 pale short bar pattern; flagellum somewhat shorter than fifth peduncular segment; flagellum with two articles, terminal flagellar segment 1.7 times as long as basal one.
Pereon (Figs 1A, 3B) covered with faint tubercles, pereonite 1–2 with relatively rounded posterolateral margin, and 3–7 with gradually pointed. Noduli Laterales on pereonites 1−4 distinctly more distant from lateral margins than ones on pereonites 5−7. Pereonite 1 with tip of anterolateral margin, reaching middle of cephalon. All pereonites with “concave-convex-concave” margin. The segments of first five pereopods with brown irregular patterns.
Pereopod 1 (Fig. 2A) with brush of strong setae on sternal margins of merus and carpus. Pereopods 2–6 almost with similar structure, all with more or less setae on six segments (Fig. 2B–F). Pereopod 7 (Figs 2G, 3I), basis oblong with some small setae on inner and outer margin; ischium triangular with couple of 2 strong setae at distal outer corner and 5–6 setae on outer margin; for male, carpus of pereopod 7 rectangular with several setae on inner margin, and long setae at distal outer corner and expanded on tergal margin.
Pleon (Figs 1A, 3B, H) narrower than pereon. Telson (Figs 1A, 3B, H) triangular in distal part with slightly concave sides and rounded apex, surpassing protopod of uropod but not reaching middle of exopod of uropod; exopod of uropod (Figs 1A, 3B, H) relatively long, almost 1.5 times as long as telson; exopod of pleopod 1 (Figs 1E, 3D) with long hind lobe bearing deep hollow and one short seta at apex, outer margin with no setae; endopod (Figs 1F, 3E) straight with triangular apical part slightly bent outwards and rather long. For male, endopod of pleopod 2 (Figs 1G, 3F) elongated in distal part; exopod triangular with line of strong setae on outer margin. Pleopods 3–5 (Fig. 1H–J) with line of setae on lower margin. Uropod (Fig. 1D) with trapezoidal basis; endopod linear and short narrow but stout with 2–3 long setae at the tip and many spines and setae around the margin; exopod 1.6 times as long as endopod.
Allotype ♀ (IOA19080602) length 10.37 mm, maximum width 4.80 mm. Endopod of first two pleon are not specialized into genitalia (Fig. 1K, L). Carpus of female pereopod 7 smoothed on tergal margin (Figs 2H, 3J).
Distribution. China (Fig. 4).
Etymology. The specific name, chevronus refers to all pereonites of the new species with “wave type ” posterior margin.
Remarks. According to the characteristic of Mongoloniscus genus, the new species should be placed in this genus. But it can distinguish from other known 17 species by all pereopods with posterior waved type margin and pleon without any pattern.
From the morphological point of view, the new species is most similar to M. sinensis. However, it differs from the latter in following characters: (1) all pereonites posterior margin with “wave type ”, concave-convex-concave (M. sinensis with smooth curve); (2) the middle of pleon without paler pattern (M. sinensis with paler longitudinal pattern); (3) telson triangular with concave sides (M. sinensis with linear sides).
From the molecular point of view, the species described in this paper, M. koreanus, M. sinensis and M. vannamei clustered into a branch, belonged to the genus Mongoloniscus. Mongoloniscus and Lucasioides - Protracheoniscus - Hemilepistus are a sister group. The new species is found clustering together with M. koreanus (Fig. 5). Indeed, male of the new species and M. koreanus with similar exopod of pleopod 1. But the new species differs from M. koreanus in following characters: (1) all pereonites posterior margin with “wave type ”, concave-convex-concave (M. koreanus with smooth curve); (2) noduli laterales of epimera of pereonites 1–7 not arranged in a line (M. koreanus with pale spots on a line). The striking difference between this new species and M. vannamei is epimera of pereonites 2–7 with a white margin (M. vannamei without a white margin).
description: Published as part of Yang, Lina & An, Jianmei, 2021, A new species of the genus Mongoloniscus Verhoeff, 1930 (Crustacea: Isopoda: Agnaridae) from China, pp. 265-274 in Zootaxa 5060 (2) on pages 268-271, DOI: 10.11646/zootaxa.5060.2.7, http://zenodo.org/record/5627272