﻿Descriptions of two new flightless species of Pseudocsikia Schimmel & Platia (Coleoptera, Elateridae, Dimini) from Taiwan Island, China, with a definition of the formosana species-group

﻿Abstract Two new flightless click beetle species, Pseudocsikiachouisp. nov. and Pseudocsikiachanjuansp. nov., are described and illustrated from Taiwan, China. Their habitus and diagnostic characters are illustrated. The two species most resemble P.formosana, which is endemic to Taiwan, by the strongly protruding pronotal anterior angles accompanied by pits and the shape of aedeagus. They can be all grouped as the P.formosana-species group. A key to the species of the P.formosana-species group and an updated checklist of Chinese Pseudocsikia with supplementary notes on type localities are provided. The discovery of two new species highlights the potential species-richness of the flightless click-beetles on Taiwan Island.


Material and methods
The specimens were softened in hot water, and genital segments were excised and dissected after treatment in 80 °C 10% KOH for 10 min. Habitus images were photographed using a Canon EOS RP + Mount Adapter EF-EOS R + a Laowa 25 mm F2.8 2.5-5× Ultra Macro Lens (for Canon EF); diagnostic characters were made using a Leica M205A stereomicroscope and a Leica DFC 550. All figures (Figs 1-5) were modified in Adobe Photoshop CC 2019. Body length was measured from the anterior margin of the head to the apex of the elytra, pronotal length was measured at midline, pronotal width was measured both at the widest point and between hind angles, and body width was measured at the widest place of the elytra. The generic concept of Pseudocsikia follows Schimmel and Platia (1991) and Schimmel (1996a). The holotypes of the new species are deposited in the Invertebrate Collection of Mianyang Normal Uni-versity, Mianyang, Sichuan, China (MYNU). The holotype and one paratype of P. formosana are deposited in the Bernice Pauahi Bishop Museum, Honolulu, Hawaii, USA (BPBM). The collecting data is quoted verbatim (in Chinese) in quotation marks. Translation of the data, as well as additional information, is given in square brackets.

Pseudocsikia formosana-species group, here defined
Diagnosis. Anterior angles of pronotum lateroapically protruded, with anterior edge of pronotum mesally concave in dorsal view. Each protrusion with sides almost parallel in dorsal view, with concavity laterally and a deep pit at basal portion (Figs 2E,3C,4C). Hypomeron with long carination parallel to pronotosternal suture and following curved outline of anterior protrusion of hypomeron, with small pit on the inside edge (Figs 2F, 3D, 4D). Male genitalia ( Fig. 5) with robust median lobe, distal half enlarged, variously shaped. Parameres short, stout, about half as long as median lobe. Phallobase with thickened outlines, and medially with longitudinal line. Remarks. The P. formosana-species group is known only from Taiwan and is possibly endemic. All three species are easily distinguished from congeners by the structure of anterior angles of pronotum, which are stoutly protruded, with a abrupt concavity laterally, and with a large deep pit at the basal portion of each protrusion. Such characters are not present in the type species of Pseudocsikia, P. rustica (Schimmel and Platia 1991), or any other Pseudocsikia species (Schimmel and Platia 1991;Schimmel 1993Schimmel , 1996aSchimmel , 1996bSchimmel , 2006. Within Dimini, protruded anterior angles of pronotum can be found in several other Dimini, like for example, Platiana Schimmel, 1993 or most species of Parapenia Suzuki, 1982(Suzuki 1982Schimmel 1996a), but the protrusions in these species are more or less gradually narrowed to a point, and either with larger pits located anteriorly or with only small, shallow pits. These unique characters of Taiwanese Pseudocsikia suggest a possible need for a new genus to accommodate them. However, they should be kept in Pseudocsikia until evidence from a detailed revision or phylogeny is available.
Comparison. This species superficially resembles P. fomosana by the pale coloration of its pronotum and elytral sides and by the sparse punctures of pronotum, but it can be easily distinguished from the latter by the larger body length (5.9 mm, while 4.0 mm in P. formosana), darker coloration of pronotum and elytra medially, more forwardly protruded anterior angles of pronotum (pointing more outward in the pronotum of P. formosana), and shorter and more divergent posterior angle of pronotum (longer, more robust and nearly straight in P. formosana). The shape of aedeagus also readily differentiates these two species. Based on the illustration of Ôhira (1972: fig. 3), the distal half of the median lobe of P. formosana has four large acute processes laterally, and its apex is somewhat rectangular; and the paramere of P. formosana has the apex rounded and slightly outward.
Head including eyes 0.5 times as wide as pronotum. Supra-antennal carinae short, directed mesad and fading medially so that median portion of frontoclypeus is not formed by sharp carina; frontoclypeus overhanging base of labrum in lateral view. Head surface sparsely punctate; punctures small, intervals between punctures mostly equal 2-3 puncture diameters. Maxillary palpus with palpomere III longer than wide. Antenna ( Fig. 3E) surpassing hind angle of pronotum by about one antennomere; scape robust and longest, remaining antennomeres subequal in length; ultimate antennomere obliquely truncate, with apex rounded. Pronotum ( Fig. 3A) wider than long (measured at midline), widest near middle. In lateral view, pronotum convex. Anterior angles of pronotum protruding (Fig. 3C); protrusion of anterior angle subquadrate, inner angle more protruded than outer angle, posterior part of protrusion with deep, crescent-shape pit. Lateral margins of pronotum arched medially, sides near middle narrowing anteriad and posteriad, anteriorly narrowing more sharply than posteriorly; posterior angles ( Fig. 3F) long, slightly divergent, apical portion of posterior angle slightly enlarged, then narrowed, apex blunt. Disc of pronotum sparsely covered with small, shallow punctures; intervals between punctures on average subequal to four to six puncture diameters; interstices smooth. Pubescence mostly directed outwards; basal portion directed anteriorly. Hypomeron ( Fig. 3B) more densely punctate than pronotum, punctures small and shallow, intervals between punctures on average subequal to 3-4 puncture diameters; apex of hypomeron strongly protruded, margin wrinkled. Pronotosternal sutures nearly straight, anterior excavation wide, long carination paralleled with suture from base of hypomeron and reaching anterior protrusion of hypomeron, forming hook-shaped carination anteriorly, end of the carination slightly extending backwards, with a small pit partly enclosed by curving hook of carination (Fig. 3D). Prosternum (Fig. 3B) including prosternal process about 2.00 times as long as wide; chin piece with large, dense punctures, intervals between punctures approximately one puncture diameter; punctures in remaining area sparser and smaller, intervals between punctures 3-6 puncture diameters, punctures on prosternal process sparse, small. Prosternal process ( Fig. 3H) with ventral surface horizontal in lateral view, with elongate notch ventroapically, roundly enlarged dorsoapically.
Aedeagus (Fig. 5D-F) with robust median lobe, two times as long as one paramere; distal half of median lobe arrow-shaped, apex with small protrusion, apex blunt, laterally with small acute projections; long, needle-like sclerite present on ventral side of median lobe. Paramere stout, reaching half of median lobe; apex pointed outward. Phallobase subquadrate, margins thickened, medially with longitudinal thickened line, basal angles rounded.
Comparison. This species can be distinguished from P. formosana and P. choui sp. nov. by the denser punctures of pronotum and larger body size (6.3 mm versus 4.0-5.9 mm). This new species can be further distinguished from P. choui sp. nov. by the more outwardly protruded anterior angles of pronotum, and the larger and straight posterior angle of pronotum. The shape of aedeagus also differs from these. The median lobe of P. chanjuan sp. nov. has a slightly enlarged and rounded apex and two small acute processes laterally near midlength, its paramere is rounded at apex but with small process subapically, and the phallobase is less rounded basally than those of the other two species.
Body generally brown, pubescence yellow (Fig. 1B). Head (including antennae and mouthparts), pronotum, elytra (except apical portions), underside (except last two sternites and lateral portion of abdomen) brown. Pronotum with paler lateral margins (in dry condition). Legs, apical portion of elytra, the last two sternites, and lateral portion of abdomen yellowish brown.
Head including eyes 0.5 times as wide as pronotum. Supra-antennal carinae short, directed mesad and fading medially so that median portion of frontoclypeus is not formed by sharp carina; frontoclypeus overhanging base of labrum in lateral view. Head surface with intervals between punctures mostly equal 1-2 puncture diameters. Maxillary palpus with palpomere III longer than wide. Antenna (Fig. 4E) simple, surpassing hind angle of pronotum about 1½ antennomeres; scape robust and longest, antennomere II shortest, antennomere III longer than antennomere II, antennomeres IV-X subequal in length, ratio of antennomeres II-IV and XI = 1: 1.1: 1.3: 1.5, ultimate antennomere tapered apically, apex pointed. Pronotum (Fig. 4A) large, subquadrate, wider than long (measured at midlines), widest near middle. In lateral view, pronotum convex. Anterior angles (Fig. 4C) of pronotum protruded, protrusion of anterior angle subquadrate, inner angle protruded almost same degree as outer angle; prostrusion with deep, narrow and curved gap. Lateral margins of pronotum roundly arched medially, sides near middle more or less evenly narrowing anterad and posterad in similar degree, posterior angle (Fig. 4F) straight, less divergent, pointing straightly toward elytra, apex blunt, inner margin with small protrusion. Disc of pronotum densely covered with small, deep punctures; intervals between punctures on average subequal to 2-4 puncture diameters; interstices smooth. Pubescence directed outwards; basal portion directed forwards.
Hypomeron (Fig. 4B) more densely punctate than pronotum, punctures moderate and deep, intervals between punctures on average subequal to 1-2 puncture diameters, apex of hypomeron strongly protruded, margin wrinkled. Pronotosternal sutures nearly straight, anterior excavation deep and narrow; long carination paralleled with suture from base of hypomeron and reaching anterior protrusion of hypomeron, forming elongate U-shaped carination anteriorly; end of the carination extending backwards, with a straight, elongate pit partly enclosed by curving hook of carination (Fig. 4D). Prosternum (Fig. 4B) including prosternal process 2.2 times as long as wide; chin piece with dense and large punctures, intervals between punctures on average subequal to half to one puncture diameter; punctures in remaining area slightly sparser and smaller, intervals between punctures on average subequal to 1-2 puncture diameters. Prosternal process (Fig. 4H) ventrally straight in lateral view, ventroapically with notch; small process in notch acutely enlarged dorsoapically.
Checklist of Pseudocsikia species from China, with notes on their type localities Pseudocsikia formosana (Ôhira, 1972) Chinese common name: 台湾伪斯叩甲.

Discussion
In China, the tribe Dimini is represented not only by the lineages with flying species, but also by flightless ones, such as those from genera Dima Charpentier, 1825, Neodima Schimmel & Platia, 1992, and Sinodima Kundrata, Sormova & Qiu, 2019Kundrata et al. 2019aKundrata et al. , 2019b. Most of these flightless species are known from the western mountains of China (12 spp. of Dima and four spp. of Neodima) (Qiu et al. , 2020Ruan et al. 2018;Kundrata et al. 2019b;Qiu 2021), with very few species from central (one sp. of Dima and one sp. of Sinodima) and eastern China (two spp. of Dima) (Suzuki 1979;Qiu et al. 2018;Ruan et al. 2018;Kundrata et al. 2019a). Previously only one flightless species of Dimini was formally reported by Suzuki (1979) from Taiwan Island, i.e., Dima nebriomorpha Suzuki, 1979. The two flightless Dimini species from Taiwan described in this paper are morphologically similar to but also readily distinguishable from Pseudocsikia formosana. The original description of P. formosana did not reveal whether it has reduced hind wings or not (Ôhira 1972), but based on the similarity of the elytral humeri and metaventrite between P. formosana and the two new species, we suppose that P. formosana also lacks or has reduced hind wings. The most notable characters supporting this hypothesis are the globose elytra and abdomen, the rounded elytra shoulders, and a relatively short metaventrite. These all are typical characters for the flightless species in Coleoptera (Smith 1964). The discovery of two more non-flying species in Taiwan indicates that the diverse flightless Dimini may be present not only on mainland East Asia but also on islands.
and Hao Xu (MYNU) for help locating the name "Bukai", and to Yong-Ying Ruan, Tamás Németh, and Hume Douglas (Editor) for their critical remarks on the manuscript. This research was supported by the Grant from Mianyang Normal University (no. QD2021A29).