﻿Two new species of the genus Symphylella (Symphyla, Scolopendrellidae) from China and the significance of the frons chaetotaxy

﻿Abstract Symphylellamacrochaetasp. nov. and Symphylellalongispinasp. nov. from China are described and illustrated. Symphylellamacrochaetasp. nov. is characterized by 10 extremely long macrosetae arranged as 4/4/2 on the frons, tergites with broad triangular processes, and 4+4 setae on the first tergite. Symphylellalongispinasp. nov. is characterized by a thick and prominent labrum, distinctly long proximal spines on the mandible, eight macrosetae arranged as 4/2/2 on frons, 3+3 setae on first tergite, and narrow triangular processes on the tergites. Detailed comparisons of the new species with similar species are presented. In addition, the frons chaetotaxy of Symphylella is illustrated and discussed for the first time and proposed as a significant diagnostic character for the taxonomic study of the genus.

Etymology. From the Greek words "macro" meaning "large" and "chaeta" meaning "seta". The species name "macrochaeta" is feminine and refers to extremely long setae on the frons.
Distribution. China (Shanghai, Zhejiang). Remarks. Symphylella macrochaeta sp. nov. has 10 extremely long macrosetae on the frons, which can distinguish it from all other congeners. It is similar to S. communa from East China and S. asiatica Scheller, 1971 from India and Sri Lanka in the shapes of the central rod, tergites, and leg 12, but the new species differs in the chaetotaxy of the first tergite (4+4 setae in S. macrochaeta sp. nov. and S. communa vs 3+3 setae in S. asiatica) and in the shape of stylus (slender in S. macrochaeta sp. nov. vs subconical in S. communa and conical in S. asiatica). The new species can also be compared to S. macropora from Tibet in the shape of tergites and processes, but it can be easily separated by the shape and the size of the opening of the Tömösváry organ (moderate and round in S. macrochaeta sp. nov. vs large and elongate in S. macropora). Description. Adult body 2.4 mm long in average (1.8-2.6 mm, n = 6), holotype 2.4 mm (Fig. 4A).
Etymology. The species name is derived from the Latin words "longus" and "spina" meaning "long spine". It is feminine and refers to the extremely long proximal spines on the pars molaris of the mandible.
Distribution. Known only from the type locality. Remarks. Symphylella longispina sp. nov. has a thickened and prominent labrum and irregular bladder-shaped organs on antennae, which separate it from all other congeners. It is most similar to S. asiatica Scheller, 1971 from India and Sri Lanka in the shape and chaetotaxy of the tergites, but the new species differs in the distal part of the processes (distinctly swollen in S. longispina sp. nov. vs small and slender in S. asiatica), in the shape and chaetotaxy of cerci (subcylindrical and with sparse setae in S. longispina sp. nov. vs conical and with dense setae in S. asiatica), and in the shape of the palp of the first maxilla (slightly curved in S. longispina sp. nov. vs straight in S. asiatica). The new species is also similar to S. brincki Scheller, 1971 from Sri Lanka in the chaetotaxy of the tergites, but they can be easily separated by the central rod (with a middle node-like interruption in S. longispina sp. nov. vs with a narrow transverse interruption in S. brincki), by the end of the processes (with round end-swellings in S. longispina sp. nov. vs spatulate end-swellings in S. brincki), and by the shape and chaetotaxy of cerci (3.3-3.8 times as long as wide and with sparse setae in S. longispina sp. nov. vs 2.3 times as long as wide and with dense setae in S. brincki).

Discussion
Symphylella is one of the most common and diverse group of symphylans with a wide global distribution (Szucsich and Scheller 2011;Bu and Jin 2018). The central rod on the head, the Tömösváry organ, the processes of tergites, the stylus, and the cercus are commonly used as diagnostic characters for species of this genus and, thus, were previously described and illustrated in detail (Scheller 1971;Szucsich and Scheller 2011). However, in recent years, we have found that some of characters, such as the first maxilla, the mandible, and the head chaetotaxy, are differ among species and good for species diagnosis , 2020), but they were often overlooked by former specialists.
The mandible structure of Symphyla was carefully studied and compared with other arthropods by former colleagues (Richter et al. 2002;Edgecombe et al. 2003). According to their excellent scanning electron photomicrographs, the mandibular gnathal edge of Hanseniella (Scutigerellidae) is composed of the pars incisivus (pi) and pars molaris (pm), with lacinia mobilis inserted between. We have observed the similar parts in the species of Symphylella (Scolopendrellidae) using light microscopy, but the shape and composition of each part are different to that of Hanseniella. The structure of mandible is varied among species of Symphylella, which can be diagnostic character of species. To obtain a better perspective overall of mandible structures in Symphyla, the study of more species using SEM method is needed.
In our study of Symphylella specimens from Zhejiang and Shanghai, we observed that the extremely long setae on the frons of S. macrochaeta sp. nov. differ from other Chinese congeners (Fig. 3H). Thus, we checked the other four species recorded in  China and compared their frons chaetotaxy (Fig. 6A-D). As a result, we confirmed that the frons chaetotaxy is a useful diagnostic character in the taxonomy of Symphylella (Table 7). According to our observations, the frons of Symphylella spp. often has well-differentiated macrosetae located on the 2/3 anterior part and 5+5 setae on the lateral margin. The quantity, length, arrangement, and ratio to antero-central seta of the macrosetae vary among species but vary little among conspecific individuals (Table 7). A broader study to reexamine the type materials of all other described species of Symphylella is needed to supplement the missing data.