Notes on the genus Trigonotoma from China, with descriptions of two new species (Carabidae, Pterostichinae)

Abstract The genus Trigonotoma in China is studied, with descriptions of two new species, T. digitatasp. nov. and T. constrictasp. nov. One species is reported as new to China, Trigonotoma indica Brullé, 1834. Species relationships within Chinese Trigonotoma are briefly discussed mainly based on the endophallic characters.


Introduction
Trigonotoma is a genus under the subtribe Trigonotomina (Carabidae: Pterostichini) which can be easily recognized by the very short and wide mentum tooth. A total of 51 Trigonotoma species has been recorded mainly from Oriental Region (Roux et al. 2016). However, only three species were distributed in China: T. lewisii Bates, 1873 widely distributed in east Asia and abundant, T. dohrni Chaudoir, 1852 widely distributed in south China but relatively rare, and T. sinica Dubault, Lassalle & Roux, 2011 only recorded in Yunnan Province and very rare (Bates 1873, Dubault et al. 2010, Chaudoir 1852, Dubault et al. 2011. Herein, two new species and a new record are proposed. The taxonomic value of the everted endophallus of Carabidae has been recognized in recent decades, both for systematics and species identification Liang 2015, Zhu et al. 2018). Thus, we studied the male endophallus of all available Chinese species (five of six known species, except Trigonotoma sinica) and briefly discuss possible relationships of some of the species.
The primary purposes of this paper are to describe two new species of Trigonotoma, provide a key for Chinese Trigonotoma species determinations, and describe and illustrate the endophallus of five Chinese Trigonotoma species (except for T. sinica) and discuss their relationships.

Materials and methods
This paper is based primarily on examination of specimens from China. The majority of specimens examined, including all types of new species, are deposited in the collection of the Institute of Zoology, Chinese Academy of Sciences, Beijing, China (IZAS). The specimens examined or cited from other collections are indicated with abbreviations.

Key to Chinese species of
Comparison. The new species is different from all other known species of Trigonotoma by its distinct male genitalia (Fig. 3). At first glance, the new species is very similar to T. lewisii in external appearance, but these two species can be readily distinguished by the differences of metepisternum and male genitalia.
Head with vertex smooth; frontal impressions deep and straight, longitudinally extending to the level of midpoint of eyes; labrum and clypeus both with anterior margins deeply emarginate; temporae straight, not swollen behind eyes; antennae reaching pronotum basal quarter.
Pronotum slightly transverse, PW/PL = 1.24, widest near anterior third; lateral margins curved in middle, and then gently narrowed to base, PW/PBW = 1.55; lateral margins straight in front of posterior angles, posterior angles rounded, not forming distinct angle; anterior margin straight, anterior angles widely rounded; posterior margin of nearly same width as anterior margin, gradually extended backward at lateral sides; disc completely glabrous, gently convex; median line fine but clearly defined, almost reaching posterior margin. Basal fovea deep and glabrous, without puncture or wrinkle; inner and outer grooves well defined, region between them deeply depressed, inner groove straight, slightly longer than curved outer groove.
Elytra oviform, EL/EW = 1.63, widest near posterior third; basal ridge complete, curved at fourth interval; humeral angles rounded, without teeth; intervals fairly convex, striae deeply incised, with coarse punctures; parascutellar striae short, apex almost conjunct to first stria; parascutellar pore present; third interval without setigerous pore; umbilicular series on ninth interval composed of approximately 25 pores, sparse in middle. Ventral side: Propleuron and mesoepisternum with sparse and coarse punctures; metepisternum short and wide, ML/MW = 1.02, with sparse and coarse punctures; abdominal sternites glabrous on middle, with a few coarse punctures on lateral sides of sternites II and III, and shallow wrinkles on lateral sides of all sternites.
Legs: Metatarsomeres I and II strongly carinate on basal 3/4 of outer surface, distinctly carinate on basal half of mesotarsomere I and metatarsomere III; fifth tarsomeres of all legs with three or four pairs of spines ventrally.
Median lobe of male genitalia bent approx. 45° (the included angle between apical lamella and axes of basal portion of aedeagus). Apical orifice long and sinuate, constricted in middle, opened dorsally, and slightly turned to left. In dorsal view, right margin of aedeagus straight, and then sinuate before apical lamella; left margin with a digitiform lobe near midpoint of apical orifice, deeply notched anterior to lobe, and then widely arched reaching apex of apical lamella; apex of digitiform lobe rounded and bent to dorsal side; apical lamella short and wide, length approx. half its basal width; strongly bent to right, apex truncated, without tooth; dorsal surface without ridge.
Endophallus (Fig. 4) rotated to dorsal-left direction of aedeagus, major portion of endophallus on dorsal side of aedeagus; gpl folded so, invisible in Fig. 4; bb elongated, extended from apical orifice to middle part of endophallus; cp at left margin of apical orifice. Three distinct lobes recognized: bl moderately large, slightly prolonged, located at base of apical orifice, pointing to apical direction of aedeagus, membranous, without scales; lb small, rounded, located at base of endophallus and left side of apical orifice, pointing to left basal direction of aedeagus; la smaller than lb, rounded, located at left side of endophallus, with fine scales. Apex of endophallus large, elongate, with heavy spines on central and basal surfaces, and fine scales on other areas.
Distribution. Yunji Mountain, Xinfeng, Guangdong. Only known from the holotype. Etymology. The specific epithet digitata is based on the Latin for finger and indicates the finger-shaped lobe on the aedeagus of the males. It is treated as an adjective in the nominative singular. Diagnosis. Dorsal side bicolored, pronotum metallic dark green, elytra dark purple; pronotum strongly narrowed to the base; posterior angles obtuse-rounded; pronotal base including the basal fovea completely glabrous; basal fovea with inner and outer grooves vaguely defined, anterior half separated from each one, posterior half fused together; metepisternum short and wide, length subequal to its basal width.
Comparisons. This new species can be readily distinguished from all other Trigonotoma from China by the narrowly constricted pronotum base. Trigonotoma concinna from Java has the pronotum shape and basal fovea very similar to T. constricta, but differs by its larger size (19-21 mm), longer metepisternum, and longer apical lamella of the aedeagus.
Head with vertex smooth; frontal impressions deep and straight, longitudinally extending to the level of midpoint of eyes; labrum and clypeus both with anterior margins deeply emarginate. Temporae straight, not swollen behind eyes; antennae reaching pronotum basal quarter.
Pronotum wide and round, PW/PL = 1.39, widest slightly before middle; lateral margins strongly widened and curved near middle, and then strongly constricted to base, PW/PBW = 1.81; lateral margins straight before posterior angles, posterior angles obtuse, forming indistinct angles; anterior margin straight, anterior angles widely rounded; posterior margin with width approximately equal to that of anterior margin, very slightly extended backward at lateral sides. Disc completely glabrous, gently convex; median line fine but clearly defined in middle, gradually shallowed, reaching neither posterior nor anterior margin; basal fovea deep and glabrous, without puncture or wrinkle; inner and outer grooves vaguely defined, partly fused together, region between them deeply depressed, so that basal fovea forms simple depressions.
Ventral side: Propleuron glabrous, mesoepisternum with dense and coarse punctures; metepisternum short and wide, ML/MW = 0.99, with dense and coarse punctures; abdominal sternites glabrous on middle, with a few coarse punctures on lateral sides of sternites II and III, and shallow wrinkles on lateral sides of all sternites.
Legs: Metatarsomeres I and II strongly carinate almost along their full length of outer surface, very shallowly carinate on basal half of mesotarsomere I and metatarsomere III; fifth tarsomeres of all legs with three or four pairs of spines ventrally.
Median lobe of male genitalia bent approximately 60° (the included angle between apical lamella and axes of basal portion of aedeagus). Apical orifice long and wide, reaching basal fourth of aedeagus, opened dorsally, slightly turned to left; right margin of apical orifice straight, left margin gently sinuate and notched near middle. In lateral view, aedeagus apex slightly bent downwards; ventral margin almost straight; apical lamella slightly thickened near base. In dorsal view, aedeagus apex broadly bent to right side; apical lamella length subequal to its basal width, with an indistinct oblique ridge, apex rounded-truncate, without tooth. Endophallus (Fig. 8) rotated to dorsal-left direction of aedeagus, major portion of endophallus on dorsal side of aedeagus; gpl folded so, invisible in Fig. 8, bb short, not reaching middle part of endophallus; cp at left margin of apical orifice. Seven distinct lobes recognized: bl moderately large, slightly prolonged, located at base of apical orifice, pointing to apical direction of aedeagus, membranous, without scales; lb-1 small, rounded, located at base of endophallus and left side of apical orifice, pointing to left basal direction of aedeagus, without decorations; lb-2 larger than lb-1, elongate, located at right side of lb-1, pointing to left apical direction of aedeagus, without decoration; la smaller than lb-1, rounded, located at left side of endophallus, with fine scales; al-1 small, rounded, located at right basal side of endophallus, without decoration; al-2 slightly larger than al-1, rounded, located at right apical side of endophallus, decorated with very fine scales; al-3 with same size as al-2, rounded, located at left apical side of endophallus, decorated with fine scales. Apex of endophallus large, elongate, with a list of heavy spines on central surface, and fine scales on other area.

Trigonotoma indica Brullé, 1834, new record
Supplementary descriptions on endophallus. Endophallus (Fig. 12) bent to dorsal direction of aedeagus, major portion of endophallus on dorsal side of aedeagus; gp located at approx middle of aedeagus, oriented to aedeagal base; gpl large, rounded, membranous, bb absent; cp absent. Four distinct lobes recognized: bl moderately large, slightly prolonged, located at base of apical orifice, pointing to apical direction of aedeagus, with a few scales on left side; ll moderately large, divided into several sublobes, located at left side of endophallus, with fine scales; rl smaller than ll, rounded, located at right side of endophallus, with fine scales; al large, divided into several sublobes, located at apex of endophallus, connected with base of endophallus through a narrow area, forming a dumbbell-shape, with fine scales. Middle of endophallus large, rounded, with a V-shaped sa on left middle and fine scales on apex.
Remarks. It is expected this species would be found to be widely distributed in and around China. Identification is based on the comparison of the image of holotype (Roux et al. 2016) and specimens from Andhra Prad., India. Compared with the specimens from India, T. indica from Mêdog is slightly larger and more vividly green on its pronotum.

Discussion
Before the present study, three Trigonotoma species were recorded from China. Here, we add three more species bringing the total number of Chinese Trigonotoma to six. Preliminary conclusions on species relationships within Chinese Trigonotoma, mainly based on the endophallic characters, are presented below.
The endophallus characters of T. constricta and T. digitata are very similar, sharing the same bb, cp, bl, la and dorsal-left rotation. Their main differences are that in T. digitata, lb is divided into lb-1 and lb-2 and three apical lobes (al-1, al-2 and al-3) appear on apex of endophallus, which makes it more complex than in T. constricta. In addition to characteristics of the endophallus, the short metepisternum is another important shared character state. As we discussed in the previous paper (Zhu et al. 2018 (Nepal), T. cylindriceps Straneo (India), T. igneicollis Bates (Myanmar), and T. buehleri Straneo (Indonesia, Sumba). The two newly described Chinese species are hypothesized to be closely related, possibly sister species, based on the character of metepisternum, the shared dorsal-left curled endophallus, and the adjacent distributions.
Two previously described species were also studied. The endophallus of T. lewisii and T. dohrni show extensive similarity but are quite different from T. digitata and T. constricta. They have a shared character of a prolonged, straight, and nearly glabrous endophallus without any lobe, scale, setose, band, or chitinized piece. Moreover, bl, cp, and bb are also absent. These two species are different from each other in the orientation of endophallus: T. lewisii extending to genital apex, slightly deflected to dorsum, gonopore oriented to aedeagal apex (Fig. 23), while T. dohrni markedly deflexed to the right, forming a right angle with aedeagus, and gonopore oriented to the right side of aedeagus (Fig.  22). As to the external characters, they have completely different pronotal form but similar long metapisternum. Additionally, they are both widely distributed in south China, Myanmar, and Vietnam, while T. lewisii is also distributed in north China, Korea, and Japan (Fig. 24). In conclusion, a close relationship of these two species is possible.
The endophallus of T. sinica has not been examined. Trigonotoma indica is different from the species discussed above in terms of endophallus characters, external characters, and distribution. The endophallus of T. indica is bent in the dorsal direction and the gonopore is oriented toward the aedeagal base. In addition, cp and bb are absent, but a V-shaped sa appears on the left middle of endophallus. And the posterior angle is pointed and forms a right angle in T. indica. In all other Chinese Trigonotoma, however their pronotum lateral margin differs, it is not pointed. Outside of the Chinese fauna, there are five other species with pointed Additionally, the endophallus of the first two are bent in a dorsal direction and the gonopore is oriented towards the aedeagal base (Roux et al. 2016), the same as T. indica. Finally, considering the different distribution patterns and morphological characters, T. indica could be related to the above Indian species and distant from other four Chinese species.