Ligidium gracilentum, Li, 2017

Li, Wei-Chun, 2017, Morphology and molecules reveal high species diversity of Ligidium (Crustacea: Oniscidea: Ligiidae) in Jiangxi, China, Zoological Journal of the Linnean Society 179 (3), pp. 627-641 : 638-639

LIGIDIUM GRACILENTUM SP. NOV. ( FIGS 6 , 7)

Diagnosis

Unique in characters of the male pleopod 2 endopod: the subapical part bears a thorn-shaped process on outer margin, and the apical part is slender and concave on inner margin.

Description

Body length of male 5.0 mm, of females 4.0 – 6.0 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. 6A ): First article narrowed basally, broadened distinctively 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 narrowed towards two distal setae at the tip.

Antenna ( Fig. 6B ): Second and third article of peduncle both with long seta near distal tip; fourth article covered with tiny setae; fifth article with four long setae at base, bears one and three long setae at distal 2/5 and distal tip, respectively; flagellum composed of 14 articles.

Mandibles ( Fig. 6C, D ): Left mandible with three-toothed incisor; lacinia mobilis three-toothed; single penicil between lacinia mobilis and molar process. Right mandible with three-toothed incisor; lacinia mobilis nearly ovate; three penicils between lacinia mobilis and molar process.

Maxillule ( Fig. 6E ): Inner lobe with three stout penicils and short seta near distal margin; outer lobe with nine apical teeth of various sizes.

Maxilla ( Fig. 6F ): Covered with tiny spines near apical tip, two setose penicils, one ovate and one elongated.

Maxilliped ( Fig. 7A): Endite nearly rectangular, distal margin with ovate process at inner distal angle; palp with five setae.

Telson ( Fig. 7B): Distal margin slightly convex near middle, gently concave near lateral margin and forming blunt, rounded corners.

Uropod ( Fig. 7B): Uropodal protopod about three times as long as broad; inner-distal projection of protopod slightly longer than basal width; endopod nearly twice as long as exopod, ending with long seta; exopodal tip with small distal seta.

Male – pereopods ( Fig. 7C–E): Pereopod 1 basis with three setae on both inner and outer margins; ischium outer margin concave and equipped with three setae, inner margin bears four setae; merus with seven setae on inner margin and three setae at outer distal angle; carpus with five setae on inner margin and three setae at outer distal angle; propodus bears four small setae on inner margin and single small seta at outer distal tip. Pereopod 7 basis distal 1/4 narrowed, bears two setae and single seta on inner and outer margin, respectively; ischium narrow basally, broadened towards subtip, then narrowed towards distal tip, bears four setae on both inner and outer margins; merus with five setae on inner margin and three setae at outer distal angle; carpus bears six setae on inner margin and four setae at outer distal angle; propodus bears four small setae on inner margin; dactylus with two small spines and a cluster of setae near apical tip.

Male – pleopods ( Fig. 7F–J): Pleopod 1 exopod with blunted rounded distal margin, endopod with triangular projection and three setae. Pleopod 2 exopod nearly ovate; endopod long and thin, apical 1/3 tapered towards blunt, rounded tip; apical part slender, concave on inner margin, outer margin well sclerotized and bears subapical, thorn-shaped process.

Holotype

Male: China, Jiangxi Province, Shangrao, Wuyishan (26 ° 54 0 N, 116 ° 42 0 E), c. 900 m a.s.l., 8.viii.2012, W. Li leg., DNA no. L14082 ( Fig. 1 ).

Paratypes

Four females, same data as the holotype, DNA nos L14083 and L14085 ( Fig. 1 ) .

Distribution and habitat

This species is only known from Jiangxi Province, China. The type locality is nearby a mountain stream in a laurel forest .

Etymology

From the Latin gracilentus (= slender), referring to the slender apical part of the male pleopod 2 endopod.

Remarks

This species is similar to L. acutangulum and L. polyacanthum sp. nov. but can be distinguished from the latter species by the slender and bent apical part of male pleopod 2 endopod. Additionally, in L. acutangulum and L. polyacanthum , the apical part of male pleopod 2 endopod is nearly triangular and straight. The species can also be distinguished based on the results of the phylogenetic analysis conducted here as stated under L. polyacanthum .

Figures

Figure 1. Maximum likelihood tree obtained from the phylogenetic analysis of concatenated 12S and 16S rRNA sequences; values given above the nodes of branches are bootstrap supports for each node. The scale bar represents the number of substitutions per site. The tree is unrooted. Abbreviation: L., Ligidium.

Figure 6. Ligidium gracilentum sp. nov., holotype; A–D, dorsal view; E–F, ventral view. A, antennule; B, antenna; C, left mandible; D, right mandible; E, maxillule; F, maxilla.