Otostigmus tricarinatus, Chen & Jiang & Huang, 2023

Chen, Tian-Yun, Jiang, Chao & Huang, Lu-Qi, 2023, A new species of Otostigmus (Chilopoda, Scolopendromorpha, Scolopendridae) from China, with remarks on the phylogenetic relationships of Otostigmus politus Karsch, 1881, ZooKeys 1168, pp. 161-178 : 161

Otostigmus tricarinatus sp. nov.

Figs 1B, D , 3 , 4 Chinese name 三棱耳孔蜈蚣

Material examined.

Holotype. CMMI 20210316103, China: Guangxi Zhuang Autonomous Region: Guiping: Xishan Town , 23.1147°N, 109.5947°E, 16 March 2021, coll. Mengxuan Shi.

Paratypes. 1 spm, CMMI 20210316161, same data as holotype; 4 spms CMMI 20200712008-011, same data as holotype, 12 July 2020 ; 1 spm, CMMI 20220327101, China: Guangxi Zhuang Autonomous Region : Nandan County, 27 March 2022, coll. Yongxiao Luo. 3 spms, CMMI 20220327102-104; Hezhou: Babu District , 24.3751°N, 111.9739°E, 27 March 2022, coll. Xusheng Zhou. Yunnan Province: Maguan county , 1 spm, CMMI 20200817001, 23.01°N, 104.39°E, 17 Aug. 2020, coll. Yanan Li. Pingbian Miao autonomous county, 1 spm, CMMI 20210315101, back mountain of Pingbian Memorial Park , 22.9884°N, 103.6931°E, 1380 m asl., 15 March 2021, coll. Chao Jiang. China: Guizhou Province: Libo County: Jiaou Township , 1 spm, CMMI 20220123101, 25.3017°N, 107.6708°E, 23 Jan. 2022, coll. Quanyu Ji.

Etymology.

The name refers to the characteristics of the tergites. The tri - compounded with the Latin Otostigmus carinatus refers to the three sharp keels on the tergites.

Diagnosis.

Antennae with 17 articles, basal three glabrous dorsally, the apical article with a well-developed lateral depression. TT 3-20 with three longitudinal keels. SS 2-19(20) with paramedian sutures occupying anterior 20-100% of sternites, a median depression, and two posterolateral depressions. Coxopleural process with 1-3 apical spines and none or one lateral spine, pore-free median longitudinal strip in pore field from the posterior of sternite 21 to the end of coxopleural process. The ultimate leg prefemur typically with 0-7 spines, lacking corner spine.

Holotype (CMMI 20210316103) description.

Body length 26 mm. Antennae and anterior 1/2 of the cephalic plate, tergites and legs have blue colouration; posterior 1/2 of the cephalic plate, forcipule segment, and sternites have yellow colouration.

Antennae with 17 articles, 3 glabrous dorsally, 2.5 glabrous ventrally, apical article double the length of the penultimate, with a well-developed lateral depression (Fig. 3A ). Antennae reach the posterior margin of T2 when reflexed. Forcipular coxosternite slightly wider than long and lacking sutures/sulci. Coxosternal tooth-plates wider than long, with four teeth. Trochanteroprefemoral process bears one apical and one lateral tubercle.

T1 lacks sutures and convex granules, T2 has sparse convex granules, TT3-21 has scattered convex granules. Tergites without paramedian sutures, TT3-20 with three sharp longitudinal keels, T21 with three incomplete longitudinal keels. Lateral margination at TT3-21. SS2-20 with paramedian sutures occupying anterior 80-100% of sternites (Fig. 3D ).

The left coxopleural process has one apical and one lateral spine and the right one has two apical and one lateral spine (Fig. 3F, G ). Pore-free median longitudinal strip in pore field from the posterior of sternite 21 to the end of coxopleural process. The ultimate legs are long and slender, with the left prefemur having one ventrolateral and one ventromedial spine. Right prefemur with one ventrolateral spine, one ventromedial spine, and one dorsomedial spine. Ultimate leg relatively long with dense setae (Fig. 3H ). Dorsal surface of ultimate prefemur with convex granules, lacking corner spine. Legs 1-5 with two and legs 6-20 with one tarsal spur. Legs 1 and 2 with one tibial spur: leg 1 with one prefemoral and one femoral spur.

Variation in paratypes.

Body length 16-50 mm (maximum in CMMI 20220123101). Cephalic plate and T1(2) lacking sutures and convex granules, antennae reached posterior margin of T2-3. Antennae only display 2.5 articles that are glabrous dorsally in the specimen CMMI 20220123101.

Lateral margination at TT 2(3)-21. SS2-20 with paramedian sutures occupying anterior 20-100% of sternites. Coxopleural process with 1-3 apical spines, 0-1 lateral spine and lacking a dorsal spine. Ultimate leg prefemur with 0-7 spines: VL 0-1, M 0-3, VM 1-3, DM 1-2, lacking corner spine. Legs 1-3(4 or 5) typically with two tarsal spurs, subsequent legs to 20, with one tarsal spur.

Remarks.

Schileyko (1995) described " O. amballae Chamberlin, 1913" on specimens from Vietnam. The morphology of these specimens is different from that of the holotype of O. amballae (see Lewis 2002) and were found to be identical to O. tricarinatus sp. nov. that has three well-developed longitudinal keels in TT3-20, a very short coxopleural process with no dorsal spine, an ultimate prefemur with two ventral spines, and lacking a corner spine. The holotype of O. amballae possesses a low median keel at TT3-20, paramedian sutures each in a sulcus from approximately T13, with two lateral keels on each side of sutures; the coxopleural process is moderately long with a single dorsal spine; the ultimate prefemur with VL3, M3, VM2, DM2, and one corner spine. Lewis (2002) further noted that all specimens assigned to O. amballae by Schileyko (1995) should be reassessed.

The material here assigned to O. tricarinatus sp. nov. refers to two geographically separate groups: the Yunnan-Guizhou plateau population (Fig. 4 ) and the Guangxi population (Fig. 3 ). They are different in the following characteristics: 1) 80% paramedian sutures on sternite in the former population compared to 20% paramedian sutures on sternite in the latter; 2) the ultimate leg prefemur with 4-7 spines in the former population compared to 1-4 spines in the latter; 3) the pore-free median longitudinal strip in pore field absent in the former population while found from the posterior of sternite 21 to the end of coxopleural process in the latter population. Furthermore, phylogenetic analysis revealed that Guangxi population is a sister group to O. politus congeners + Yunnan-Guizhou plateau population and has strong node support from both ML and BI analyses (PP = 1, BS = 97%). They are considered to be the same species because no more reliable identification characteristics could find.

Distribution.

Fig. 2 . China: Guangxi Zhuang autonomous region, Yunnan Province, Guizhou Province; Vietnam ( Schileyko 1992, 1995, 2007; Vu et al. 2020).

Phylogenetic analysis.

We obtained sequences consisting of 658-812 bp COI, 408-423 bp 16S rRNA, and 368-886 bp28S rRNA. The average K2P genetic distance is 20.1% between Otostigmus species, and the range of the K2P distance between Otostigmus species is 17.2% ( O. voprosus against O. astenus to 23.1% ( O. politus yunnanensis against O. beroni ) (Table 3 ). The intraspecific divergence among Otostigmus taxa varied from 0% to 18.2% ( O. aculeatus ). The mean distance within O. tricarinatus sp. nov. was 16.0%(Table 4 ), which is relatively high among Otostigmus species. The interspecific divergence between O. tricarinatus sp. nov. and the other Otostigmus species fell within a range of 18.4% ( O. spinosus ) to 21.9% ( O. angusticeps ). The interspecific divergence between O. tricarinatus sp. nov. and O. politus yunnanensis (21.1%) was higher than O. tricarinatus sp. nov. and O. politus politus (19.3%). The high genetic distances found within the Otostigmus species imply that they may have been misidentified or contain cryptic species. Therefore, species delimitation of Otostigmus requires further study with additional samples as well as genetic data from various populations.

Sequences from the new species, as well as 47 other Otostigminae samples from different species groups, were aligned. Included in the alignment were two COI sequences from samples IEBR-Chi 013 and IEBR-Chi 036 from Vietnam, which were misidentified as " O. amballae Chamberlin, 1913" ( Vu et al. 2020). ML and BI analyses were utilised to construct phylogenetic trees for the combined COI+16S+28S dataset. Our results moderately supported the Otostigmus politus group, Otostigmus aculeatus group, and species of the Otostigmus rugulosus group, from both ML and BI analyses (BS> 70% and PP> 0.9) (Fig. 5 ). The reciprocally monophyletic Otostigmus politus group and Otostigmus aculeatus group were found to have moderate levels of support (PP = 1; BS = 71%). In this study, O. tricarinatus sp. nov. was assigned to the Otostigmus politus group. Otostigmus tricarinatus sp. nov. (Yunnan-Guizhou plateau population) and one sample from Vietnam: Me Linh (IEBR-Chi 013) was determined to be sister to O. politus politus and O. politus yunnanensis , with strong node support (PP = 1 and BS = 97%). Otostigmus tricarinatus sp. nov. (Guangxi population) together with one sample from Vietnam, Ta Xua (IEBR-Chi 036), was observed as having high levels of support for being sister to the clade of O. politus politus + O. politus yunnanensis + O. tricarinatus sp. nov. (Yunnan-Guizhou plateau population) in both BI and ML analyses (PP = 1, BS = 97%).

At last, the key for Otostigmus species in China is provided.

Figures

Figure 1. Live specimens of Otostigmus spp. from China A O. p. politus B O. tricarinatus sp. nov. (Guangxi population) C O. p. yunnanensis D O. tricarinatus sp. nov. (Yunnan-Guizhou plateau population).

Figure 2. Distribution of O. politus species, O. tricarinatus sp. nov., and O. amballae s. l. in China and Vietnam.

Figure 3. Otostigmus tricarinatus sp. nov. (Guangxi population) CMMI 20210316103 (HOLOTYPE) A cephalic plate (dorsal view) B forcipular segment and sternite 1 (ventral view) C Forcipular tooth-plates (ventral view) D SS 12 - 14 (ventral view) E TT 10 - 12 (dorsal view) F LBS 21 (ventral view) G LBS 21 (lateral view) H Prefemur of left ultimate leg. Scale bars: 1 mm.

Figure 4. Otostigmus tricarinatus sp. nov. (Yunnan-Guizhou plateau population) CMMI 20210315101 A cephalic plate (dorsal view) B forcipular segment and sternite 1 (ventral view) C Coxosternal tooth-plates (ventral view) D SS 3 - 5 (dorsal view) E Tergites 7 - 9 (ventral view) F Tergite 21 G Sternite 21 and coxopleural process (ventral view) H Prefemur of ultimate leg (ventral view); I Prefemur of ultimate leg (dorsal view). Scale bars: 1 mm.

Figure 5. Maximum likelihood phylogenetic tree and Bayesian phylogenetic tree based on combined data for Otostigmus along with posterior probability (PP> 0.9 / BS> 70 %) values for each node.