Acroterius gen. nov. (Araneae: Linyphiidae: Linyphiinae) with twelve new species from Yunnan, China

Acroterius gen. nov. is described from Yuannan, together with twelve new species: A. absentus gen. et sp. nov. (♂); A. brevis gen. et sp. nov. (♂/♀); A. camur gen. et sp. nov. (♂/♀); A. circinatus gen. et sp. nov. (♂/♀); A. hamatus gen. et sp. nov. (♀); A. inversus gen. et sp. nov. (♀); A. latus gen. et sp. nov. (♂/♀); A. longidentatus gen. et sp. nov. (♀); A. longimultus gen. et sp. nov. (♂/♀); A. longiprojectus gen. et sp. nov. (♀); A. ovatus gen. et sp. nov. (♀), and A. parvus gen. et sp. nov. (♀). Detailed descriptions of genitalic characters and somatic features by means of photographs and line drawings, as well as comparisons with closely related species, are provided.


Introduction
Yunnan, the most southwestern province of China, is bordering with Laos, Vietnam, Myanmar and has seven climate zones (north tropical, south tropical, central subtropical, north subtropical, warm temperate, temperate and plateau climate areas). Its average temperature is about 5~24°C. Yunnan Province has a very rich and diverse linyphiid spider fauna as was demonstrated by Irfan et al. (2019), who described a new genus Zhezhoulinyphia Irfan, Zhou & Peng, 2019, and by Irfan & Peng (2018, 2019a, 2019b, who mentioned three genera new to China along with six new species, i.e., Herbiphantes acutalis Irfan & Peng,

Etymology
The generic name is an arbitrary combination of letters. Gender masculine.
Head. Cephalic region slightly elevated, yellowish to dark brown; fovea, cervical and radial grooves distinct; sternum longer than wide, green to yellowish to dark brown with spine-like hairs; labium wider than long, dark brown; maxillae long, distal end broader with scopulae. Eye region narrow, AER recurved, PER procurved slightly wider.
abdoMen. Oval, dorsally with pattern extending down to the base of spinnerets followed by irregular white patches dorso-laterally, and ventrally pale, greenish to brown with or without irregular white patches ( Fig. 4A-B).
epigyne (Figs 8,13,17,22,27,32,37). Anterior wall of epigyne wider than long; posterior margin of anterior wall with a projection on each side; copulatory openings European Journal of Taxonomy 743: 1-53 (2021) situated inside the atrium between the anterior wall and posterior median plate, connected with long, semicircular copulatory ducts joined to the spermathecae. Posterior median plate posteriorly with a parmula of variable length with a socket ventrally. Spermathecae slender, present near the posterior median plate. Fertilization ducts long, present laterally on the posterior median plate, extending mesally.

Differential diagnosis
The new species can be distinguished from all other species of Acroterius gen. nov. by the absence of radical apophysis (Figs 1A-C, 3A-B).

Etymology
The species name comes from the Latin adjective 'absens', meaning 'absent', referring to the radical apophysis absent in male palp.
cHeLicerae. With five promarginal and five retromarginal teeth, promargin with deep depression and with small teeth except proximal two long; proximal second tooth much longer and almost touching upper margin of fang, distal three teeth small ( Fig. 2A

Female
Unknown.

Etymology
The species name comes from the Latin adjective 'brevis' meaning 'short', referring to the short radical apophysis in male palp.

Etymology
The species name comes from the Latin adjective 'camur', meaning 'curved' and referring to the curved distal suprategular apophysis in the male palp.

Etymology
The species name comes from the Latin adjective 'circinatus', meaning 'circular' and referring to the circinate-shaped copulatory ducts in the ventral view of the epigyne.
Variation in tHe epigyne (HNU-Tang-04-09, Fig. 21A-F). We noticed in the four out of five female paratypes that the epigynal parmulas are broken at the same point due to unknown reasons. All the other somatic and genitalic characters are found to be similar ( Fig. 21A-D).

Male
Unknown.

Male
Unknown.

Distribution
China (Yunnan Province, Fig. 38).  (Figs 30B, D, 31B). The posterior projection of the anterior wall of the epigynal plate is wider than long and doesn't protrude beyond the epigastric furrow ( Fig. 27A-B), but is longer than wide and protruding beyond the epigastric furrow in A. longimultus gen. et sp. nov. (Fig. 32A-B). The distal part of the spermathecae is hook-shaped (Fig. 27D), but inverted L-shaped in A. longimultus gen. et sp. nov. (Fig. 32D).

Differential diagnosis
The new species resembles Acroterius brevis gen. et sp. nov. (Fig. 8A-D) in having a similar short parmula as in A. camur gen. et sp. nov. and A. longidentatus gen. et sp. nov. and the C-shaped distal part of spermathecae in epigyne (Fig. 29A-D); it can be distinguished by: the posterior projection of the anterior wall of the epigynal plate C-shaped in ventral view, somewhat triangular in lateral view and retained below the lateral margin of anterior wall of the epigyne in the new species (Fig. 29A-C), but beak-shaped in ventral view, protruding above the lateral margin in A. brevis gen. et sp. nov. (Fig. 8A-C).

Etymology
The species name comes from the Latin adjective 'longus' + 'dentatus', meaning 'long' + 'teeth' and referring to the long and highly sclerotized teeth on the retrolateral margin of the chelicerae in the female.
cHeLicerae. With six promarginal and six retromarginal teeth; reteromarginal teeth long and highly sclerotized. epigyne. Parmula 0.36 long, 0.23 wide at base (Fig. 29B); the posterior projection of anterior wall of epigynal plate circular in ventral view; somewhat triangular and retained below lateral wall of epigynal plate in lateral view (Fig. 29A-C). Spermathecae slender, distal part C-shaped and situated near median septum (Fig. 29D). . The posterior projection of the anterior wall of the epigynal plate is longer than wide, protruding beyond the epigastric furrow ( Fig. 32A-B), but wider than long, not protruding beyond the epigastric furrow in A. latus gen. et sp. nov. (Fig. 27A-B). The distal part of spermathecae inverted L-shaped (Fig. 32D), but hook-shaped in A. latus gen. et sp. nov. (Fig. 27D).

Etymology
The species name comes from the Latin adjective 'longus' + 'multus', meaning 'long' + 'much' and referring to the very long distal suprategular apophysis in the male palp.

Differential diagnosis
The new species resembles Acroterius hamatus gen. et sp. nov. (Fig. 19A-D) in having long parmula in epigyne (Fig. 34B-E); it can be distinguished by: the posterior projection of the anterior wall of the epigynal plate longer than wide (Figs 34B-C), but wider than long in A. hamatus gen. et sp. nov. (Figs 19A-B, 21A-B). In ventral view, the distal part of parmula is not expanded (Fig. 34B-C), but distinctly expanded in A. hamatus gen. et sp. nov. (Fig. 19A-B). The spermathecae are not curved (Fig. 34E), but the tip is curved, pointing towards the posterior margin of the epigyne in A. hamatus gen. et sp. nov. (Figs 19D, 21D).

Etymology
The species name comes from the Latin adjective 'longus' + 'projectus' meaning 'long' + 'projection', referring to the long posterior projection of the anterior wall of the epigynal plate in the epigyne.

Male
Unknown.

Differential diagnosis
The new species resembles Acroterius longidentatus gen. et sp. nov. (Fig. 29A-C) in having a similar circular posterior projection of the anterior wall of the epigynal plate in the epigyne (Fig. 36A-C); it can be distinguished by the anterior wall of the oval epigynal plate margin (Fig. 36A-B), but semicircular in A. longidentatus gen. et sp. nov. (Fig. 29A-B). In dorsal view, parmula with wave-like margin and almost four times as long as median septum (Fig. 36D), but tongue-shaped and as long as median septum in A. longidentatus gen. et sp. nov. (Fig. 29D). The spermathecae are hook-shaped (Fig. 36D), but C-shaped in A. longidentatus gen. et sp. nov. (Fig. 29D).

Etymology
The species name comes from the Latin adjective 'ovatus', meaning 'oval' and referring to the oval anterior wall of the epigynal plate margin of the epigyne.

Male
Unknown.

Differential diagnosis
The new species resembles Acroterius brevis gen. et sp. nov. in having similar hook-shaped spermathecae; it can be distinguished by the triangular parmula, shorter than the median septum in the new species (Fig. 37A, D), but tongue-shaped and longer than the median septum in A. brevis gen. et sp. nov. (Fig. 8A-B, D).

Discussion
Based on illustrations and morphological characters provided by Merrett (1963), Acroterius gen. nov. can be identified as a member of the subfamily Linyphiinae given that: a claw is present on the female palp; the male palp lacks a tibial apophysis; the maxillae are long and parallel; and all tibiae have two dorsal spines. The discovery of this new genus is not surprising, considering that there is limited taxonomic research on Linyphiidae from Yunnan. Zhao & Li (2014, 2017, Irfan & Peng (2018, 2019a, 2019b and Irfan et al. (2019) already identified 39 species and 10 genera; with the addition of Acroterius gen. nov., the number of linyphiid genera endemic to Yunnan is now eleven. Acroterius gen. nov. appears to be closely related to Zhezhoulinyphia as many species in both genera have been recorded from the same localities and they share similarities in the embolic division and spermathecae shape. Considering their morphological similarities and overlapping distribution, it is possible that these genera are sister taxa and their ancestor originated in the mountains of southwestern Yunnan. However, more taxonomic and phylogenetic studies need to be done on Linyphiidae from Yunnan and across the adjacent areas to understand the distribution and origins of these taxa.