Research Article |
Corresponding author: Lihong Tu ( tulh@cnu.edu.cn ) Academic editor: Dimitar Dimitrov
© 2015 Ming Yan, Xiaokai Liang, Lihong Tu.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Yan M, Liang X, Tu L (2015) On the desmitracheate “micronetine” genus Nippononeta Eskov, 1992 (Araneae, Linyphiidae). ZooKeys 484: 95-109. https://doi.org/10.3897/zookeys.484.8663
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The desmitracheate system in a “micronetine” genus Nippononeta Eskov, 1992 is recognized for the first time in the present study. This makes the subfamilial placement of this genus problematic. A morphological study was conducted for N. kurilensis Eskov, 1992 (the type species of Nippononeta) and N. coreana (Paik, 1991). Characters of genitalia and tracheal system, as well as some somatic characters were studied in detail by using scanning electronic microscopy (SEM), and compared with those of Agyneta. Updated descriptions of the genus Nippononeta and its two species are presented. Putative synapomorphies for Nippononeta and Agyneta are provided, as well as some putative synapomorphies shared by the two genera. The results imply that both scaped epigynum and desmitracheate tracheal system are probably homoplastic. The placement of Nippononeta and Agyneta within Linyphiidae need to be resolved in future studies.
Taxonomy, desmitracheate, scaped epigynum, genital morphology, “micronetine”
Linyphiidae Blackwall, 1859 is the second largest spider family, including over 4,500 species (
Classical taxonomy of Linyphiidae is often confusing because of the characters overlapping among groups. The currently accepted seven subfamilies are based on different characters. For example, the epigynum furnished with a scape carrying copulatory grooves and openings (referred to as “scaped epigynum” below) was used as the main diagnostic feature for Micronetinae Hull, 1920 (
Micronetinae is a large subfamily, which currently includes 1212 species placed in 91 genera (
In the present study, we report another “micronetine” genus Nippononeta Eskov, 1992, having a scaped epigynum, but also a desmitracheate system. The genus Nippononeta was separated from Agyneta, the senior synonym of Meioneta (Eskov, 1992). We conducted a morphological study of Nippononeta. Characters of the genitalia and tracheal system, as well as some somatic characters, were documented with SEM images for N. kurilensis Eskov, 1992 (the type species of Nippononeta) and N. coreana (Paik, 1991), and compared with those of Agyneta, as well as those of Erigoninae. Putative synapomorphies were proposed for Nippononeta and Agyneta, which need to be tested in future studies.
Specimens were examined and measured using a Leica M205A stereomicroscope. Male palps and epigyna were examined after they were dissected from the body. Left structures (e.g. palps, legs, etc.) were depicted. Embolic divisions were excised by breaking the membranous column which connects the suprategulum and the radix. Male palps and epigyna were cleared in methyl salicylate. Scanning electron microscopy (SEM) images were taken under a Hitachi S-3400N scanning electron microscope at the China Agricultural University. For SEM examination, the specimens were prepared following
AC aciniform gland spigot(s)
AG aggregate gland spigot(s)
ALS anterior lateral spinneret
CY cylindrical gland spigot(s)
FL flagelliform gland spigot
MAP major ampullate gland spigot
mAP minor ampullate gland spigot
PI piriform gland spigot(s)
PLS posterior lateral spinneret
PMS posterior median spinneret
Male palp
ARP anterior radical process
AX apex of embolus
CRL cymbial retrolateral lobe
DTA distal tibial apophysis
E embolus
EBT embolus basal tooth(teeth)
EC embolus column
EM embolic membrane
EP embolus proper
LC lamella characteristica
P paracymbium
PF proximal cymbial fold
PH pit hook
PHS pit hook sclerite
PTP proximal tibial process
R radix
RTP retrolateral tibial process
SPT suprategulum
T tegulum
TA terminal apophysis
TH thumb of embolus
Epigynum
CG copulatory groove
DP dorsal plate
LL lateral lobe on sacpe
SC scape
ST stretcher
TDF transversal dorsal fold of epigynum
TP turning point of copulatory groove
VP ventral plate
The genus includes 24 species; the type species is Nippononeta kurilensis Eskov, 1992.
Nippononeta species are similar to Agyneta in many genital characters and the desmitracheate system, but differ in the presence of a dorsal pattern on the abdomen, which is absent in most Agyneta. Male palps of Nippononeta can be distinguished from Agyneta by the conical elevation on the cymbium absent in the former (Fig.
Nippononeta kurilensis. A–G male palp A retrolateral B ventral C anteroventral D detail of A, arrows indicate the serrated surface of DTA (upper), median branch of paracymbium (left) and outer margin fold continue with distal arm (lower) E–G embolic division E dorsal F ventral, arrow indicates basal hook of embolus G embolus, ventral, upper arrow indicates the last strongest spine of thumb; lower arrow indicates basal hook of embolus H anterior part of male abdomen, ventral, shows epiandrous gland spigots absent. ARP anterior radical process; AX apex of embolus; CRL cymbial retrolateral lobe; DTA distal tibial apophysis; E embolus; EC embolus column; EM embolic membrane; EP embolus proper; LC lamella characteristica; P paracymbium; PF proximal cymbial fold; PH pit hook; PHS pit hook sclerite; R radix; RTP retrolateral tibial process; T tegulum; TA terminal apophysis; TH thumb of embolus.
Nippononeta kurilensis. A–D epigynum. A ventral B dorsal C caudal D anterior E tracheal system, with soft tissue digested F female palp G female spinneret spigots, arrow indicates MPA nubbin on ALS H male PLS spigots. AC aciniform gland spigots; AG aggregate gland spigots; ALS anterior lateral spinneret; CG copulatory groove; CY cylindrical gland spigots; FL flagelliform gland spigot; MAP major ampullate gland spigot; mAP minor ampullate gland spigot; PI piriform gland spigots; PLS posterior lateral spinneret; PMS posterior median spinneret; SC scape; ST stretcher; TP turning point; VP ventral plate.
Chelicerae of normal size, with narrowed fang base and stronger stridulatory ridges in the male than in the female (Fig.
Male palp (Fig.
Epigynum (Figs
China, Japan, Korea, Russia.
N. kurilensis Eskov, 1992: 159, f. 27–30 (Dmf);
1♂ and 1♀ (CNU), Russia, Sakhalin Island, near Novoalexandrovsk, 11 Sept. 1992, A. Basarukin leg.
The male of N. kurilensis is distinguished from N. coreana and all other Nippononeta species by: 1) the absence of proximal tibial process (Fig.
Nippononeta coreana. A–F male palp. A retrolateral, arrow indicates outer margin tooth B detail of A, arrow indicates outer margin tooth C ventral D detail of C E embolic division, ventral F embolus, dorsal G male body with soft tissues digested, shows tracheal system H anterior part of male abdomen, ventral, shows epiandrous gland spigots absent. ARP anterior radical process; AX apex of embolus; DTA distal tibial apophysis; E embolus; EBT embolus basal teeth; EC embolus column; EM embolic membrane; EP embolus proper; LC lamella characteristica; P paracymbium; PF proximal cymbial fold; PH pit hook; PHS pit hook sclerite; PTP proximal tibial process; R radix; RTP retrolateral tibial process; TA terminal apophysis; TH thumb of embolus.
Somatic and genital characters as in the genus description.
Russia (Sakhalin, South Kuril Islands) and Japan (Hokkaido).
Macrargus coreanus Paik, 1991: 2, f. 30-38 (Df).
Nippononeta coreana:
2♂ and 2♀ (CNU), China, Sichuan Province, Tianquan County, Mt. Erlangshan Natural Forest Park, 8 July 2004, L. Tu leg.
See the diagnosis of N. kurilensis.
Other genital characters see the description by
Nippononeta coreana. A–D chelicerae A male, front B female, front C male, ectal D female, ectal E female palp F–G spinnerets F female G male, PMS spigots H male PLS spigots. AC aciniform gland spigots; AG aggregate gland spigots; ALS anterior lateral spinneret; CY cylindrical gland spigots; FL flagelliform gland spigot; MAP major ampullate gland spigot; mAP minor ampullate gland spigot; PI piriform gland spigots; PLS posterior lateral spinneret; PMS posterior median spinneret.
China (Guangxi, Hunan, Hubei, Jilin, Sichuan), Korea.
The putative synapomorphies based on genital characters suggest that the four desmitracheate “micronetine” genera: Nippononeta, Agyneta, Tennesseellum, and Anibontes have a common ancestor.
The results of phylogenetic analyses support the single origin of desmitracheate system (
Comparative studies on the tracheal morphology suggest that the transformation between haplotracheate and desmitracheate systems is not a result of a single morphological change. A total of five characters were proposed to allocate interspecific variation of tracheal anatomy in Linyphiidae (
Furthermore, we find that, in addition to the desmitracheate system, some confirmed synapomorphies of erigonines (
We thank Gustavo Hormiga, Yuri M. Marusik and Dimitar Dimitrov for their comments on an earlier version of this paper. We also thank Andrei Tanasevitch for kindly providing the specimen of N. kurilensis for this study, thank Victor Fet and Wenjing Lin for checking English. The study was supported by National Natural Sciences Foundation, China (NSFC-30670244, NSFC-30970314, NSFC-30911120070), and by the Program for Changjiang Scholars and Innovative Research Team in University (IRT-13081).