Two new species of the genus Symphylella (Symphyla, Scolopendrellidae) from East China

Abstract Symphylella minutasp. nov. and Symphylella communasp. nov. from China are described and illustrated. Symphylella minutasp. nov. is characterized by the delicate and minute body, a well-developed and thin central rod with a vestige of a transverse suture in the middle, eight setae on the first tergite, pointed processes on the tergites, and short cerci with sparse setae. Symphylella communasp. nov. is characterized by the chaetotaxy of the first tergite with 4+4 setae, processes of the tergites somewhat longer or the same length with broad, most of lateromaginal setae long, anterolateral setae of tergites 2–4, 6, 7, 9, and 10 distinctly longer than other lateromarginal setae, approximately as long as the process of the same tergite, and cerci with numerous subequal and slightly curved setae. In addition, the chaetotaxic variation on the tergites, the distribution, the habitat, and the feeding habit of the genus Symphylella are discussed.


Introduction
Symphyla is an ignored group of myriapods with about 200 species reported in the world and only six species are known from China Bu 2018, 2019;. The genus Symphylella Silvestri, 1902 is a common group of symphylans Description. Adult body 1.5 mm long in average (1.2-2.2 mm, n = 8), holotype 1.4 mm (Fig. 1A).
Head length 150-170 μm, width 133-158 μm, with widest part somewhat behind the middle on a level with the points of articulation of mandibles. Central rod well developed but thin, with a vestige of a transverse suture in the middle. Anterior branches normally developed, without median branches. Dorsal side of head moderately covered with setae of different length, longest setae (18-25 μm) located most anterior on head, at least 3.0 times as long as central ones (4-6 μm). Cuticle of anterolateral part of head with rather coarse granules, around Tömösváry organ with moderate granules, other area with fine and faint granulation (Fig. 1F).
Mouthparts. Mandible with two fused lamellae and 12 teeth in total (Fig. 3A). First maxilla has two lobes, inner lobe with four hooked teeth, palp bud-like and pointed (Fig. 3D). Anterior part of second maxilla with many small protuberances each carries one seta, distal setae thicker and spiniform; posterior part with sparse setae. Cuticle of maxilla and labium covered with dense pubescence (Fig. 1G).
with six to eight setae evenly inserted around the antennal wall with interior setae (10-18 μm) slightly longer than exterior ones (6-7 μm). Chaetotaxy of third antennomere similar to preceding ones. Setae on proximal antennomeres longer than on distal ones. Proximal antennomeres with only primary whorl of setae, middle and subapical antennomeres with secondary whorl setae present. Three kinds of sensory organs observed on antenna: rudimentary spined sensory organs on dorsal side of middle antennomeres (Figs 1C, 3C); cavity-shaped organs on antennomeres 5-19 (Figs 1C, 3C); bladder-shaped organs on antennomeres 7-14 next to apical one increasing in number on subapical antennomeres to a maximum of 12 (Figs 1D, E, 3C). Apical antennomere subspherical, somewhat wider than long (width 22 μm, length 13-17 μm), with 10-13 setae on distal half; three or four spined sensory organs consisting of three or four curved spines around a central pillar in depressions on distal surface (Figs 1E, 3B). All antennomeres covered with short pubescence. Chaetotaxy and sensory organs of antennae of holotype are given in Table 1.
Trunk with 17 dorsal tergites. Tergites 2-13 and 15 each with one pair of sharp triangular processes. Length from base to tip of processes distinctly longer than its basal width except for the tergites 4, 7, 10 and 13, in which processes are almost as broad as long; basal distance between processes of tergites distinctly longer than their length from base to tip (Table 2). All processes with end-swellings. Anterolateral setae on all tergites longer than other lateromarginal setae, about 0.6-0.7 of the length of processes on same tergite. Inserted setae (setae between inner basal seta and apical setae) absent. All tergites pubescent ( Fig. 2A-H).
Coxal sacs present at bases of legs 3-9, fully developed, each with three to five setae on surface (Fig. 1I). Relevant area of leg 2, 11 and 12 replaced by two, two or three, and one to three setae respectively (Figs 1H,2I).
Sense calicles with smooth margin to pit, about same length as outer diameter. Sensory seta inserted in cup center, extremely long (90-100 μm).
Cerci short and stout (Figs 1A, 2J, 3E), about one-third of head and one-half of length of leg 12, 2.5 times as long as its greatest width (48-55 μm, 20-22 μm), inserted with sparse subequal setae, six to eight dorsal, five or six ventral, one or two outer, most setae straight, a whorl of six distal setae slightly curved, longest outer seta (14-16 μm) slightly longer than greatest width of cerci, terminal area (8-17 μm) short, 0.3-0.6 time as long as greatest width of cerci, circled by six to eight layers of curved ridges, terminal seta (20-23 μm) long, distinctly longer than terminal area.
Etymology. The species name "minuta" refers to the delicate and minute body of the species.
Distribution. China (Jiangsu, Shanghai, Zhejiang). Remarks. Symphylella minuta sp. nov. is similar to S. oligosetosa Scheller, 1971 from India and Sri Lanka in the shape of the central rod on head and the shape and chaetotaxy of the tergites. They can be distinguished by the chaetotaxy of the first tergite (eight setae in S. minuta sp. nov. vs six in S. oligosetosa), shape of the processes (pointed and with swollen ends in S. minuta sp. nov. vs strongly pointed and without swollen ends in S. oligosetosa), shape and chaetotaxy of cerci (short and stout, about 2.5 times as long as wide in S. minuta sp. nov. vs slender, 3.5-3.6 times as long as wide in S. oligosetosa). It is also similar to S. abbreviata Scheller, 1971 from Sri Lanka in the chaetotaxy of the tergites and shape of the processes, but can be easily separated by the chaetotaxy of the first tergite (with eight setae in S. minuta sp. nov. vs six setae in S. abbreviata), shape of the third tergite (without indentation in S. minuta sp. nov. vs with a distinct middle lateromarginal indentation in S. abbreviata), shape of cerci (tapering in S. minuta sp. nov. vs with outer side strongly bulging in S. abbreviata). Diagnosis. Symphylella communa sp. nov. is characterized by the chaetotaxy of the first tergite composed by 4+4 setae, processes of tergites somewhat longer or the same length with broad, most of lateralmaginal setae long, anterolateral setae of tergites 2-4, 6, 7, 9, and 10 distinctly longer than other lateromarginal setae, approximately as long as processes of the same tergite, cerci with numerous subequal and slightly curved setae. Description. Adult body 2.2 mm long in average (1.7-3.1 mm, n = 40), holotype 2.1 mm (Fig. 4A).

Symphylella communa
Head length 200-290 μm, width 200-350 μm, with widest part somewhat behind the middle on a level with the points of articulation of mandibles (Fig. 4F). Central rod distinct, divided into two parts by a node-like interruption in the middle. Anterior branches normal, median branches vestigial. Head dorsally covered with setae of different length, longest setae (25-38 μm) located most anteriorly, at least 3.0 times as long as central shortest ones (8-11 μm). Cuticle on anterolateral part of head with fine coarse granules.

Mouthparts.
Mandible with two fused lamellae and 11 teeth in total (Fig. 6A). First maxilla has two lobes, inner lobe with four hooked teeth, outer lobe with teethed apex, palp straight, conical, pointed (Fig. 6B). Anterior part of second maxilla with numerous small protuberances which carry one seta each, distal setae thicker and spiniform; posterior part with sparse setae (Fig. 4G). Cuticle of maxilla and labium covered with dense pubescence (Fig. 4G).
Trunk with 17 dorsal tergites. Tergites 2-13, and 15 each with one pair of triangular processes. Length from base to tip of processes somewhat shorter than or the same as its basal width; basal distance between processes of tergites 4-13, and 15 longer than their length from base to tip (Table 5). All processes with round swollen ends (Figs 5B-E, G). Anterolateral setae of tergites 2, 3, 4, 6, 7, 9 and 10 distinctly longer than other lateromarginal setae, approach length of process of same tergite (Fig. 5B-D), that of tergites 5, 8, 11, 13 and 15 subequal or slightly shorter than longest ones of other lateromarginal (Fig. 5E, G). Processes with one to three inserted setae. All tergites pubescent (Fig. 5B-G).
Etymology. The species name "communa" is derived from "common" which refer to the common morphology and wide distribution of the species.
Distribution. China (Jiangsu, Shanghai, Zhejiang). Remarks. Symphylella communa sp. nov. is most similar to S. asiatica Scheller, 1971 from India and Sri Lanka and S. macropora  from Tibet in the shape of the central rod, tergites, processes, anterolateral setae, and leg 12. It differs from S. asiatica and S. macropora in the size of the opening of the Tömösváry organ (moderate in S. communa sp. nov. vs very small in S. asiatica, extremely large in S. macropora) and chaetotaxy of the first tergite (4+4 in S. communa sp. nov. and S. macropora vs 3+3 setae in S. asiatica). It is also affiliated to S. neotropica (Hansen, 1903) from Brazil in the shape of tergites and processes, but can be easily distinguished by the central rod (both the anterior and posterior parts are in the same width in S. communa sp. nov. vs the anterior part is distinctly narrow than the posterior part in S. neotropica).

Discussion
The genus Symphylella is well defined by the presence of 17 tergites with 13 of them having triangular processes present on posterior margins, the first pair of legs replaced by two protuberances with a few setae inserted on, and short styli present on the base of legs 3-9. The shapes of the central rod, Tömösváry organ, tergites and their processes, and cerci, as well as the chaetotaxy of the tergites and cerci, are good characters for the species identification. The measurements of anterolateral setae on tergites are also taxonomically informative for the species definition. The number of lateromarginal setae, inserted setae, central setae, and other setae on tergites often show considerable variations among adult individuals. Asymmetrical setae are usually observed on tergites. In Symphylella communa sp. nov., most specimens with 4+4 setae on the first tergite while several specimens exhibits 4+5 and one specimens with 5+5 setae, and the same variation is also observed in S. macropora. The shape of the cerci is a relative stable character of the species, but the ratio of the length and width of the cercus may be affected by the mounting process of specimens. Therefore, caution is advised when identify the species of Symphylella, which should be based on multiple differential stable characters of fully mature specimens.
The members of the genus Symphylella are distributed in almost all faunal regions of the world: 17 species (34.7%) in Nearctic Region, 12 (24.5%) in Ethiopian Region, 11 (22.5%) in Oriental Region, 7 (14.3%) in Palaearctic Region, 6 (12.2%) in Australian Region, and two (4.1%) in Neotropical Region. Most of the species occur in Nearctic, Ethiopian, and Oriental regions. It seems they are more adaptable to the temperate climate. In China, Symphylella are often found with high density in the tropical and subtropical area. More species are expected to be discovered in East and South China in the future.
According to the previous studies, the species of the genus Symphylella are adapted to diverse habitats and a variety of biotopes: from litter and moss, soil and leaf litter in bamboo and broad-leaf forest, pineapple field, to the plantation of bananas and coco, lawn, botanical garden, tea plantation, orchards, and unoccupied sites. They can live on moist slopes of hills, along streams, in silty soil of agricultural lands, and in caves. They are also present under stone or bricks, in decaying vegetable matter, under bark, in heaps of rotten coconut shells, and under coco trunks on grassy ground (Scheller 1961(Scheller , 1971. Studies have shown that Symphylella species occupy a broad range of habitats, from the littoral intertidal areas to high mountain forests. Some species, S. asiatica Scheller, 1971, S. brincki Scheller, 1971, S. foucquei Scheller, 1971, and S. tentabundna Scheller, 1971 for instance, live in mountain areas more than 2000 m above the sea level (Scheller 1971).
Symphylella species are supposed to be phytophagous or saprophagous (Rohrbach and Johnson 2003). During our observation of the mounted specimens of S. communa sp. nov., we noticed that the intestinal tract of some individuals have many appendages, mandibles, antennae, and cuticle fragments of some other micro-arthropods such as pauropods and collembolans, so this species may be also omnivorous.