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Studies on the Stenothemusharmandi species-group (Coleoptera, Cantharidae), with descriptions of two new species from China

Abstract Background The Stenothemusharmandi species-group has 10 species at present. They are S.harmandi (Bourgeois, 1902) (located in N. India, Nepal); S.holosericus Švihla, 2005, S.orbiculatus Švihla, 2005 and S.subnitidus Švihla, 2005 (N. India); S.distortirudis Y. Yang & X. Yang, 2014, S.laticollis Y. Yang & X. Yang, 2014, S.parallelus Y. Yang & X. Yang, 2014 and S.septimus Y. Yang & X. Yang, 2014 (China: Xizang); S.fugongensis Y. Yang & X. Yang, 2014 (China: Yunnan) and S.leishanensis Y. Yang & X. Yang, 2014 (China: Guizhou). In the present study, two previously-known species are classified into this species-group, S.dentatus Wittmer, 1974 and S.alexandrae Švihla, 2004, of which the latter as a subspecies of the former is upgraded to the specific level and another two new species are discovered and described. New information Two new species of the Stenothemusharmandi species-group are described, S.acuticollis sp. n. (China: Yunnan) and S.nigricolor sp. n. (China: Xizang), which are illustrated with habitus photos and aedeagi of males, abdominal sternites VIII and internal genitalia of females. S.alexandrae Švihla, 2004 stat. n. is upgraded from a subspecies of S.dentatus Wittmer, 1974 and the two species are classified into this species-group. Characters of the female reproductive system are described for the first time for the following species: S.distortirudis Y. Yang & X. Yang, 2014; S.laticollis Y. Yang & X. Yang, 2014; S.leishanensis Y. Yang & X. Yang, 2014; S.orbiculatus Švihla, 2005; S.septimus Y. Yang & X. Yang, 2014 and S.subnitidus Švihla, 2005. Meanwhile, some additional distribution information is added for previously-described species. A key for the identification of all species is updated.


Introduction
The genus Stenothemus Bourgeois, 1907 is a moderately diverse group in Cantharidae, which contains 75 species hitherto known in total (Wittmer 1974, Okushima and Satô 1997, Okushima and Satô 1999, Švihla 2004,Švihla 2005,Švihla 2011,Hsiao 2015, Hsiao et al. 2016, Yang et al. 2014. Stenothemus can be distinguished from all other genera of Cantharinae by its simple tarsal claws in both sexes, the head with a pair of smooth impressions behind antennal fossae, pronotum with widely rounded anterior angles and laterally projecting posterior angles or quadrate with rectangular posterior angles (Švihla 2004), the fused parameres of aedeagus deeply cleft on the ventral side and the ventral process and dorsal plate of each paramere converging (Okushima and Satô 1999). Within the genus, only one species group, the S. harmandi species-group, is recognised.
The S. harmandi species-group was proposed by Švihla (2005) and, later, was reviewed by Yang et al. (2014). There are 10 species included in this group (Švihla 2005(Švihla , Yang et al. 2014, mostly distributed in the Himalayan areas with some spreading to the Yunnan-Guizhou Plateau (Yang et al. 2014). The members of this species-group are diagnosed by the distinctive aedeagus, with both ventral process and dorsal plate of each paramere bent ventrad , the ventral process thickened apically in varying degrees in lateral view and the dorsal plate greatly narrowed apically in dorsal view (Švihla 2005); the abdominal tergite VIII of female is curled ventrad to enfold the sides of sternite VIII, which is strongly narrowed posterad (Yang et al. 2014).
In the present study, two new species of the S. harmandi species-group were discovered from Yunnan and Xizang, China and described under the names of S. acuticollis sp. n. and S. nigricolor sp. n. Meanwhile, two previously-described species are added into this group, S. dentatus Wittmer, 1974 and S. dentatus alexandrae Švihla, 2004, whose females were either unknown or neglected in the original descriptions. Furthermore, it is suggested that S. dentatus alexandrae Švihla, 2004 be upgraded from the subspecific level to an independent species, on the basis of examination of the types. Additionally, the reproductive system of the female for cantharid beetles has been shown to be useful in delimitation of the species-group (Okushima 2005) or Stenothemus species ), but it has remained unknown for the S. harmandi species-group until now; herein, we present the characters of this structure for the members of this group.

Materials and methods
The studied material is deposited in the Institute of Zoology, Chinese Academy of Sciences, Beijing, China (IZAS), the Museum of Hebei University, Baoding, China (MHBU), the Naturhistorisches Museum Basel, Switzerland (NHMB) and the National Museum, Prague, Czech Republic (NMPC).
Genitalia of both sexes and abdominal sternites VIII of females were dissected and cleared in a solution of 10% sodium hydroxide (NaOH) and female genitalia were dyed with haematoxylin. In studying the morphology of the aedeagus or female genitalia, at least one specimen was dissected per species, more if any damage occurred during dissection. If the species had a rather wide distribution range, one specimen was dissected from each locality. The measurements were carried out with the aid of a Leica M205A stereomicroscope. Habitus photos were taken using a Leica M205A stereomicroscope and multiple layers were stacked using Combine ZM (Helicon Focus 5.3). Line drawings were made using a camera lucida attached to a Nikon SMZ1500 stereomicroscope, then edited in CorelDRAW 12 and Adobe Photoshop CS3.10.0.1.
Complete label data in Chinese were transliterated for type specimens. Body length was measured from the anterior margin of the clypeus to the elytral apex and body width across the humeral part of elytra. Morphological terminology of aedeagus follows that of Okushima (2005) and morphological terminology of female genitalia follows that of Brancucci (1980).

Data resources
The information of the specimens in this paper is from the preserved specimens of IZAS and MHBU, as well as the type specimens of NMPC and NHMB, examined in this study.

Diagnosis
Body is usually brown and mixed with irregular dark brown markings, except for only a few which are uniformly dark brown or black. The posterior angles of pronotum are sharply protruding laterad or obtusely rounded. The aedeagus with both ventral process and dorsal plate of each paramere are bent ventrad, the ventral process is thickened apically in varying degrees in lateral view and the dorsal plate is greatly narrowed apically in dorsal view. In the female, the abdominal tergite VIII is curled ventrad to enfold lateral sides of sternite VIII, which is strongly narrowed posteriorly.

Distribution
India.

Notes
In the original publication (Švihla 2004), S. alexandrae was treated as a subspecies of S. dentatus Wittmer, 1974. However, differences between the two taxa have been found not only in the external appearance, but also in the structure of the aedeagus. In S. alexandrae, the body is uniformly dark brown, pronotum bears projecting and sharp posterior angles (Fig. 1a) and the dorsal plates of the aedeagus are three times as long as wide and separated from each other in dorsal view (Švihla 2004: figs. 142-144). In comparison, S. dentatus has a pale yellow body, mixed with dark brown markings on the disc of the pronotum, elytra and legs (Fig. 1b) and the dorsal plates are 1.5 times as long as wide, converging in dorsal view (Švihla 2004: fig. 145). As these differences are sufficient to support their independent status, we suggest that S. alexandrae be recognised at the specific level.
Compared with others, the aedeagus of this species is distinctive from all other species, where the ventral process of each paramere is bent ventrad to a less extent, at an angle of 30 degrees to the median lobe. Probably for this reason, it was not included in the S. harmandi species-group by Švihla (2005), when he established this group. Here, it is included in this species-group, based on the structure of the aedeagus, of which both ventral process and dorsal plate of each paramere bent a b c d Figure 1. ventrad, although to a lesser extent, ventral process thickened terminally and dorsal plate narrowed apically. All these characteristics match the definition of S. harmandi species-group well (Švihla 2005), so S. alexandrae is suggested to be a member of this group.

Distribution
India.

Notes
S. alexandrae was treated as a subspecies of S. dentatus due to the similarity of aedeagus in the orginal description (Švihla 2004), suggesting their close relationship. For the same reason with S. alexandrae, S. dentatus was not included in the S. harmandi species-group by Švihla (2005). As what is noted for S. alexandrae, except for the ventral process bent ventrad to a lesser extent, other characteristics of the aedeagus of S. dentatus match the diagnosis of S. harmandi species-group well, including both ventral process and dorsal plate of each paramere bent ventrad, ventral process thickened terminally and dorsal plate narrowed apically. Therefore, we suggest S. dentatus should also be included in the S. harmandi species-group.
Body pale yellow mixed with irregular dark brown markings, except head black, with a reddish-brown marking on midline of vertex, apex of each antennomere yellow. Body densely covered with pale yellow pubescence, mixed with semi-recumbent pale yellow pubescence.
Head. Surface densely punctate, each side with a smooth, rectangular impression behind antennal fossa; eyes strongly protruding, head across eyes nearly as wide as pronotum; terminal maxillary palpomeres elongate-triangular, widest at mid-length; antennae filiform, extending to three-quarter length of elytra, antennomeres II 2.8 times as long as wide at apices, III 1.1 times longer than II, V longest, VI to X gradually shortened, XI longer than X, pointed at apex.
Aedeagus (Fig. 2). Strongly swollen dorsally at base in lateral view, strongly reduced in diameter apically; basal piece (bp, phallobase) nearly as long as dorsal plate (dp) of each paramere, with a large, bifurcate conjoined middle nodule (nd) at base of ventral side; ventral processes (vp) of parameres approaching each other in ventral view, long and thickened apically, bent ventrally at an angle of about 60 degrees to median lobe in lateral view; dorsal plates shorter than ventral processes, greatly narrowed apically (apical part about one-third as wide as basal part); laterophyses (la) rounded at apices, exceeding into emargination between dorsal plates.  Body stouter than in male, eyes smaller, head across eyes about 0.9 times width of pronotum, antennae shorter and approximately extending to elytral mid-length; elytra with lateral margins diverging posteriorly more strongly in dorsal view.
Internal organ of reproductive system (Fig. 4a) Švihla, 2005 Abdominal sternite VIII (Fig. 6a, b). Obliquely narrowed posteriorly, latero-apical angles rounded, posterior margin shallowly and roundly emarginate in the middle and arcuate on both sides, present behind the notch with a membrane which is sclerotised.

Diagnosis
Most similar to S. harmandi (Bourgeois, 1902) in the shapes of pronotum and ventral process of each paramere of the aedeagus, but differs in the aedeagus which is strongly swollen dorsally at base in lateral view, with the dorsal plate of each paramere being abruptly narrowed apically in dorsal view. Unlike in the latter, the aedeagus is moderately swollen at the basal part and the dorsal plate of each paramere is evenly narrowed apically (Yang et al. 2014: figs. 21-23). For the female, abdominal sternite VIII is shallowly emarginate in the middle of posterior margin, while deeply emarginate in S. harmandi (Yang et al. 2014: fig.11). a b c d Figure 6.
Abdominal tergite VIII and sternite VIII of female. It also resembles S. fugongensis Y. Yang et X. Yang, 2014 in the body size and colouration and the shape of ventral process of each paramere of the aedeagus, but can be easily distinguished from S. fugongensis by the pronotum with sharp posterior angles and the aedeagus has the dorsal plate of each paramere abruptly narrowed apically in dorsal view with the laterophyses being rounded at the apices in lateral view. In comparison, S. fugongensis has the pronotum with rounded posterior angles (Yang et al. 2014: fig. 3) and the aedeagus has the dorsal plate of each paramere evenly narrowed apically, with the laterophyses hooked at the apices in lateral view (Yang et al. 2014: figs. 24-26).

Etymology
The specific name is derived from the Latin acutus (sharp) and collum (neck), referring to its pronutum with sharp posterior angles.
Body black, mouth-parts pale yellow, legs dark brown. Body densely covered with short, semi-recumbent pale pubescence.
Head. Surface densely punctate, each side with a smooth, rectangular impression behind antennal fossa; eyes small, strongly protruding, head across eyes 1.1 times wider than pronotum; terminal maxillary palpomeres elongate-triangular, widest at basal one-third; antennae filiform, extending to two-thirds length of elytra, antennomeres II 2.2 times as long as wide at apices, III 1.5 times longer than II, IV nearly as long as V, XI longer than X, pointed at apex.
Elytra. Nearly parallel-sided, 3.3 times as long as combined humeral width, 4.2 times as long as pronotum, surface densely punctate, longitudinal costae hardly visible.
Aedeagus (Fig. 3). Moderately swollen dorsally at base in lateral view, strongly reduced in diameter apically; basal piece nearly as long as dorsal plate of each paramere, with a large, bifurcate conjoined middle nodule at base of ventral side; ventral processes of parameres approaching each other in ventral view, long and thickened apically, bent ventrally at an angle of 30 degrees to median lobe in lateral view; dorsal plates shorter than ventral processes, abruptly narrowed apically (apical part about one-half as wide as basal part); laterophyses rounded at apices, exceeding into emargination between dorsal plates.

Female.
Body stouter than in male, eyes smaller, head across eyes nearly as long as pronotum, antennae shorter and approximately extending to quarter length of elytra; elytra 3.1 times as long as combined humeral width.
Internal organ of reproductive system (Fig. 4b). Vagina stout, with median oviduct situated at ventro-apical part, vagina abruptly narrowed in apical part and extended into a short tube from where diverticulum and spermathecal duct are arising; diverticulum long, 0.3 times as long as adult body length, evenly thinned apically, slender tubeshaped and spiral; spermathecal duct 0.1 times as long as diverticulum; spermatheca slender tube-shaped and spiral, thinner than spermathecal duct and 0.9 times longer than diverticulum, with basal part extended into a short tube, at opening of accessory gland. Accessory gland thin in basal part and the remainder relatively thick, 0.5 times as long as spermatheca.
Abdominal sternite VIII (Fig. 6c, d). Lateral margins narrowed posteriorly, latero-apical angles obtusely rounded, posterior margin shallowly emarginate, with a protuberance in the middle and arcuate on both sides, behind the notch with a membrane which is sclerotised.

Diagnosis
It resembles S. alexandrae Švihla, 2004 stat. n. (type locality: N. India) in the structure of aedeagus, but differs in the following characters: the body is black, pronotum is 1.1 times as wide as long, of which anterior margin is arcuate, the aedeagus has the ventral process of each paramere even in width in ventral view. In comparison, S. alexandrae has a dark brown body, pronotum is 1.4 times as wide as long, of which anterior margin is nearly straight and the ventral process of each paramere is widened apically (Švihla 2004: figs. 142-144).

Etymology
The specific name is derived from the Latin niger (black) and color (colour), referring to its black body colouration.

Description
Female. Internal organ of reproductive system (Fig. 4c). Vagina elongate, with median oviduct situated at ventro-apical part, vagina abruptly narrowed in apical part and extended into a short tube from where diverticulum and spermathecal duct are arising; diverticulum long, 0.4 times as long as adult body length, evenly thinned apically, slender tube-shaped and spiral; spermathecal duct 0.2 times as long as diverticulum; spermatheca slender tube-shaped and spiral, thinner than spermathecal duct and nearly as long as diverticulum, with basal part extended into a short tube, at opening of accessory gland. Accessory gland thin in basal part and the remainder relatively thick, nearly as long as spermatheca.

Description
Female. Internal organ of reproductive system (Fig. 4d). Vagina elongate, with median oviduct situated at ventro-apical part, vagina abruptly narrowed in apical part and extended into a long tube from where diverticulum and spermathecal duct are arising; diverticulum long, 0.3 times as long as adult body length, evenly thinned apically, slender tube-shaped and spiral; spermathecal duct 0.2 times as long as diverticulum; spermatheca slender tube-shaped and spiral, thinner than spermathecal duct and 1.1 times longer than diverticulum, with basal part extended into a short tube, at opening of accessory gland. Accessory gland thin in basal part and the remainder relatively thick, 0.8 times as long as spermatheca.

Description
Female. Internal organ of reproductive system (Fig. 5a). Vagina elongate, with median oviduct situated at ventro-apical part, vagina abruptly narrowed in apical part and extended into a short tube from where diverticulum and spermathecal duct are arising; diverticulum short, 0.2 times as long as adult body length, evenly thinned apically, slender tube-shaped and spiral; spermathecal duct 0.1 times longer than diverticulum; spermatheca slender tube-shaped and spiral, thinner than spermathecal duct and nearly as long as diverticulum, with basal part extended into a short tube, at opening of accessory gland. Accessory gland thin in basal part and the remainder relatively thick, 0.9 times as long as spermatheca.

Description
Female. Internal organ of reproductive system (Fig. 5b). Vagina elongate, with median oviduct situated at ventro-apical part, vagina abruptly narrowed in apical part and extended into a short tube from where diverticulum and spermathecal duct are arising; diverticulum short, 0.1 times as long as adult body length, evenly thinned apically, slender tube-shaped and spiral; spermathecal duct 0.2 times as long as diverticulum; spermatheca slender tube-shaped and spiral, thinner than spermathecal duct and 1.1 times longer than diverticulum, with basal part extended into a short tube, at opening of accessory gland. Accessory gland thin in basal part and the remainder relatively thick, nearly as long as spermatheca.

Description
Female. Internal organ of reproductive system (Fig. 5c). Vagina elongate, with median oviduct situated at ventro-apical part, vagina abruptly narrowed in apical part and extended into a short tube from where diverticulum and spermathecal duct are arising; diverticulum short, 0.1 times as long as adult body length, evenly thinned apically, slender tube-shaped and spiral; spermathecal duct 0.3 times as long as diverticulum; spermatheca slender tube-shaped and spiral, thinner than spermathecal duct and 0.7 times longer than diverticulum, with basal part extended into a short tube, at opening of accessory gland. Accessory gland thin in basal part and the remainder relatively thick, 1.8 times as long as spermatheca.

Description
Female. Internal organ of reproductive system (Fig. 5d). Vagina elongate, with median oviduct situated at ventro-apical part, vagina abruptly narrowed in apical part and extended into a short tube from where diverticulum and spermathecal duct are arising; diverticulum short, 0.2 times as long as adult body length, evenly thinned apically, slender tube-shaped and spiral; spermathecal duct 0.3 times as long as diverticulum; spermatheca slender tube-shaped and spiral, thinner than spermathecal duct and 1.4 times longer than diverticulum, with basal part extended into a short tube, at opening of accessory gland. Accessory gland thin in basal part and the remainder relatively thick, 1.1 times as long as spermatheca.

Identification keys
Key to the species of Stenothemus harmandi species-group 1 Posterior angles of pronotum obtuse and rounded (Fig. 1b)

Discussion
The present study first illustrates the female internal organ of the reproductive system for the S. harmandi speices-group. As in other Stenothemus species , Ge et al. 2021, the oviduct is suitated at the apical part of the vagina, the spermatheca is composed of only one spiral and thin tube and the diverticulum is thinly spiral-tubed. The combination of these characters could distinguish Stenothemus from other genera of Cantharinae, such as Cantharis L. (Li et al. 2016a), Themus Motschulsky (Yang et al. 2018, Yang et al. 2019a, Yang et al. 2019b, Lycocerus Gorham ( Xi et al. 2021b, Xi et al. 2021a, Cephalomalthinus Pic and Micropodabrus Pic (Li et al. 2016b). However, we cannot summarise any common charater in this structure for this speciesgroup to be distinguished from other well-known species , Ge et al. 2021. Maybe, with the discovery of new species in the near future, some more potential characters will be explored in defining the species-group.