Ligidium polyacanthum Li, 2017, SP. NOV.
Creators: name: Li, Wei-Chun
Publisher: name: Zenodo
Year: 2017
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Isopoda
Ligiidae
Ligidium
Ligidium polyacanthum

description: LIGIDIUM POLYACANTHUM SP. NOV. (FIGS 4, 5)
Diagnosis
Unique in characters of the male pleopod 2 endopod: the subapical part bears a thorn-shaped process near outer margin, and tiny spines are present near the subapical process and apical tip.
Description
Body length of male 6.5 mm, of females 7.0 – 9.0 mm. Body elongated (c. 2.3 times as long as wide); pereonites 1 and 2 without ‘bristle field’ on posterior margin of epimera. Colour in alcohol dark grey with white spots on dorsal surface.
Antennule (Fig. 4A): First article subrectangular, gently broadened towards three distal setae at the tip; second article about 1.3 times as long as the first, ending with three distal setae; third article thin and long, distal half narrowed towards blunt tip.
Antenna (Fig. 4B): Articles 2 – 4 of peduncle all with single seta near distal tip; fifth article equipped with two setae; flagellum composed of 12 articles.
Mandibles (Fig. 4C, D): Left mandible with three-toothed incisor; lacinia mobilis three-toothed; four penicils between lacinia mobilis and molar process. Right mandible with three-toothed incisor; lacinia mobilis three-toothed; two penicils between lacinia mobilis and molar process.
Maxillule (Fig. 4E): Inner lobe with three stout penicils and long seta near distal margin; outer lobe with 12 apical teeth of various sizes.
Maxilla (Fig. 4F): Distally divided into two lappets with rounded apices; small lappet with well-developed seta; large lappet with five well-developed setae and several tiny spines, lateral margin bears two setose penicils at subapical part, one elongated and one small ovate.
Maxilliped (Fig. 5A): Endite subrectangular, basally narrow, gently broadened towards distal tip, distal margin with tooth at inner distal angle; palp with eight setae.
Telson (Fig. 5B): Distal margin arched, concave near lateral margin and forming blunt, rounded corners.
Uropod (Fig. 5B): Uropodal protopod about three times as long as broad; inner-distal projection of protopod nearly as long as width of its base; endopod about 1.5 times as long as exopod, endopodal and exopodal tips with long seta.
Male – pereopods (Fig. 5C, D): Pereopod 1 basis with four setae on inner margin; ischium concave on outer margin, bears single seta on both inner and outer margins; merus with eight setae on inner margin and two setae at outer distal angle; carpus with six setae on inner margin and single seta at outer distal angle; propodus bears some small setae on inner margin and small seta at outer distal tip. Pereopod 7 basis bears two setae on inner margin; ischium narrow and concave basally, broadened towards subtip, then narrowed towards distal tip, bears four setae on inner margin and two setae on outer margin; merus with six setae on inner margin and two long setae at outer distal angle; carpus conspicuously narrow at base, gradually broadened toward distal tip, bears five setae on inner margin and four setae at outer distal angle; propodus bears four small setae on inner margin.
Male – pleopods (Fig. 5E–I): Pleopod 1 exopod with blunt, rounded distal margin, endopod with triangular projection and long seta. Pleopod 2 exopod nearly ovate; endopod long and thin, subapically with a thorn-shaped process and several tiny spines, apically well sclerotized at outer half and tapered towards blunt, rounded tip, covered with tiny spines at the end.
Holotype
Male: China, Jiangxi Province, Ganzhou, Longnan, Jiulianshan (24 ° 40 0 N, 114 ° 33 0 E), c. 1000 m a.s.l., 23.iv.2012, W. Li leg.
Paratypes
Two females, same data as the holotype, DNA nos L14135 and L14136 (Fig. 1).
Distribution and habitat
This species is only known from Jiangxi Province, China. It was found under a thick layer of leaf-litter of Michelia species on the mountain slope in a primary forest.
Etymology
From the Latin polyacanthus (= spinous), referring to the male endopod of pleopod 2 being covered with many tiny spines at apical part.
Remarks
This species is very similar to L. acutangulum and L. gracilentum sp. nov., but it can be distinguished by the tiny spines at the apical part of the male pleopod 2 endopod. In L. acutangulum and L. gracilentum, the male pleopod 2 endopod lacks tiny spines. Further, they can also be separated based on the phylogenetic analysis of sequence data; every species was represented by a well-supported clade (Fig. 1).
description: Published as part of Li, Wei-Chun, 2017, Morphology and molecules reveal high species diversity of Ligidium (Crustacea: Oniscidea: Ligiidae) in Jiangxi, China, pp. 627-641 in Zoological Journal of the Linnean Society 179 (3) on pages 637-638, DOI: 10.1111/zoj.12464, http://zenodo.org/record/14806541