Taxonomic studies on the genus Trilacuna (Araneae, Oonopidae) from Myanmar

Abstract Six species of the genus Trilacuna Tong & Li, 2007 are reported from Myanmar, including four new species: T. besucheti Grismado & Piacentini, 2014 (♂♀), T. changzi Tong & Li, sp. nov. (♂♀), T. hponkanrazi Tong & Li, sp. nov. (♂♀), T. loebli Grismado & Piacentini, 2014 (♀), T. triseta Tong & Li, sp. nov. (♂), and T. zhigangi Tong & Li, sp. nov. (♀). Morphological descriptions and photographic illustrations of the new species are given. All types are preserved in the Institute of Zoology, Chinese Academy of Sciences in Beijing (IZCAS).

The spider genus Trilacuna was established to accommodate two new species from Southwest China (Tong and Li 2007). Subsequently, additional species have been described: seven from Thailand, Malaysia, and Sumatra (Eichenberger and Kranz-Baltensperger 2011), two from Vietnam (Tong and Li 2013), seven from Bhutan, India, Nepal, and Pakistan (Grismado et al. 2014), one from Iran (Malek-Hosseini et al. 2015), one from Korea (Seo 2017), and 10 from Southwest China (Tong et al. 2018Liu et al. 2019). Currently, the genus Trilacuna comprises 30 species, all of which are known from Asia (WSC 2020).

Methods
The specimens were examined in 95% ethanol using a Leica M205C stereomicroscope. Details were studied with an Olympus BX51 compound microscope. Photos were taken with a Canon EOS 750D zoom digital camera (18 megapixels) mounted on an Olympus BX51 compound microscope. Vulvae were cleared in lactic acid. Scanning electron microscope images (SEM) were taken in a high vacuum under a Hitachi TM3030 after critical point drying and gold-palladium coating. All measurements were taken using an Olympus BX51 compound microscope and are given in millimeters in the text. The materials are preserved in the Institute of Zoology, Chinese Academy of Sciences in Beijing (IZCAS).
The following abbreviations are used in the text and figures: Trilacuna Tong & Li, 2007: 333;Grismado et al. 2014: 26. Type species. Trilacuna rastrum Tong & Li, 2007 Diagnosis. Trilacuna differs from other oonopid genera, except those of the "Dysderoides complex" (including Bannana Tong & Li, 2015, Dysderoides Fage, 1946, Himalayana Grismado, 2014, by the enlarged male palpal femur, the very complex embolus-conductor system, and the notched labium. Males differ from the other genera of the "Dysderoides complex" by usually lacking the furrow connecting the posterior tracheal spiracles, and females differ by having a long postgastric scutum covering almost the whole ventral abdomen (Grismado et al. 2014;Tong et al. 2019).
Composition. 34 species, including four described here. Distribution. Iran to the Korean Peninsula. Diagnosis. Males of this species can be recognized by the circular, scale-like structure on the distal part of the bulb (white arrows in Fig. 2E, F) and the cymbium, which has two or three stout, dark setae with large bases (black arrows in Fig. 2G). Females are distinguished by having a darkened band (db) on the posterior margin of the epigastric furrow (Figs 3G, 15A).
Distribution. India (Meghalaya), Myanmar.        (Fig. 6G). The male of T. mahanadi has unmodified endites and lacks the dorsal branch of the embolus system, and the triangular plate is lacking in the epigastric area of the female (Grismado et al. 2014: figs 36-38).
Etymology. The specific name is derived from Chinese pinyin, "changzi", which means "long moustache", referring to the long, curved spines on the male's endites; noun in apposition.
Distribution. Known only from the type locality.     (Fig. 8E), the curved, strongly sclerotized posterior ridge (spr) of the female's epigastric area (Fig. 9G), and the reticulate carapace (Figs 7D, F, 9D, F) of both sexes. Trilacuna gongshan has three long, tooth-like lobes in the embolus system, without a curved, strongly sclerotized posterior ridge in the female's epigastric area, and with a granulate carapace in both sexes : figs 10-12, 24G, H).
Etymology. The specific name is a noun in apposition taken from the type locality. Distribution. Known only from the type locality. Diagnosis. Females of this species can be distinguished from other congeners by the semicircular plate of the epigastric area and the worm-shaped globular structure of the endogyne (Fig. 15G, H).
Description. See Grismado et al. 2014. Distribution. India (Assam); Myanmar. Variation. The specimens from Myanmar have a reticulate carapace and a nearly straight posterior eye row in dorsal view (Fig. 10D). By contrast, the specimens from India have a granulate carapace, and the posterior eye row is slightly recurved in dorsal view (Grismado et al. 2014: figs 35H, I). Diagnosis. The new species is similar to T. bilingua Eichenberger, 2011 but can be distinguished by the three black, thick setae on the endites of the male (Figs 11G, 16G, 16H) and the slender anterior branch (ab) of the embolus system (Fig. 12E, 12F, 12H). Trilacuna bilingua lacks black, thick setae on the endites, and the embolus system has two very short lobes basally (Eichenberger et al. 2011: fig. 5-6).
Female. Unknown. Etymology. The species epithet is a noun in apposition composed of the Latin words tri (three) and seta and refers to the three black, thick setae on the male's endites.
Distribution. Known only from the type locality.
Remarks. There are two species reported from a single female specimen in this study, and one described from a single male: T. loebli Grismado & Piacentini, 2014, T. zhigangi Tong & Li, sp. nov., and T. triseta Tong & Li, sp. nov., respectively. The following characters indicate that neither of the two females are conspecific with T. triseta Tong & Li, sp. nov. T. loebli is dark brown (Fig. 10A) with a reticulated carapace (Fig. 10D), and T. zhigangi has small eyes (Fig. 13A) and lacks the triangular, pointed, median projection of the clypeus (Fig. 13H). The male, T. triseta Tong & Li, sp. nov. has a reddish-brown body, a smooth carapace, normal-sized eyes, and a triangular, pointed, median projection (Fig. 11A, D Diagnosis. The new species is similar to T. bangla Grismado & Ramírez, 2014 but can be distinguished by the short, lateral apodemes (they do not reach the groove connecting the posterior spiracles) and the stick-shaped anterior sclerite of the endogyne (Fig. 15J). Trilacuna bangla has very long lateral apodemes (they distinctly extend beyond the groove connecting the posterior spiracles), and the anterior sclerite has long arms (Grismado et al. 2014: fig. 48A).
Male. Unknown.    Etymology. The species is named after Mr Zhigang Chen, one of the collectors of the holotype.
Distribution. Known only from the type locality.