Three new species of Willowsia (Collembola: Entomobryidae) from Guizhou Province, China

The genus Willowsia Shoebotham, 1917 belongs to the family Entomobryidae and has the following main characters: eyes 8+8, dens without spines or scales, mucro bidentate with a basal spine, scales present on body. Scale morphology is diversified in Willowsia. Zhang et al. (2011) divided scales into four types based on surface sculpture: spinulate type, short rib type, long basal rib type and uninterrupted type.


Introduction
The genus Willowsia Shoebotham, 1917 belongs to the family Entomobryidae and has the following main characters: eyes 8+8, dens without spines or scales, mucro bidentate with a basal spine, scales present on body.Scale morphology is diversified in Willowsia.Zhang et al. (2011) divided scales into four types based on surface sculpture: spinulate type, short rib type, long basal rib type and uninterrupted type.
Thirty-eight species have been described worldwide, ranging from the Arctic region to tropical areas.Among them, 26 species are from Asia and 17 from China.In this study, three new species from Guizhou Province, China are described: W. sexachaeta sp.nov., W. christianseni sp.nov.and W. tanae sp.nov.Similar to other Willowsia species from Guizhou Province, these new species also have scales of the spinulate type.Table 1 summarizes the main differences between all Chinese species of Willowsia.

Material and methods
After clearing in lactic acid, specimens were mounted under a coverslip in Marc André II solution, and were studied with a Leica DM2500 microscope.Images were taken with a Hitachi SN3400 scanning electron microscope and a mounted Leica DFC300 FX digital camera, and enhanced with Photoshop CS2 (Adobe Inc.).The number of macrochaetae is given by half-tergite in the descriptions.The nomenclature     (2005) and Mari-Mutt (1986).Labial chaetae are designated following Gisin (1967).Tergal chaetae of the body are designated using the system of Szeptycki (1979).

Diagnosis
Moderate size, usually 1−2 mm; eyes 8+8; antennae four segmented; mucro bidentate with a basal spine; dens without spines or scales; body with various types of scales in different species.

Etymology
Named after the characteristic six (Latin word "sex-") macrochaetae present on the central part of Abd.IV.
sCales.Hyaline, spinulate type, leaf-like and present on Ant.I−II, dorsal side of head and terga, coxa to tibiotarsus, anterior face of ventral tube and ventral side of manubrium (Figs 4B -4C).

Remarks
The new species is similar to another Chinese species, W. baoshanensis Chai & Ma, 2017, in colour pattern and scale morphology, but the difference between them in chaetotaxy is great.It is also similar to the species W. japonica (Folsom, 1897) in colour pattern on the body and three mac on Abd.I, but scale morphology is of the spinulate type in the former and the short rib type in the latter (Table 1).The differences between the three species are great, as shown in Table 2.

Etymology
In memory of Kenneth Christiansen, who gave me much help in the taxomony of Collembola.
sCales.Hyaline, spinulate type, leaf-like and present on Ant.I−II, dorsal side of head and terga, coxa to tibiotarsus, anterior face of ventral tube and ventral side of manubrium (Fig. 7E).

Remarks
The new species is similar to the species W. nigromaculata (Lubbock, 1873) in colour pattern, but scale morphology is of the spinulate type in the former and the long basal rib type in the latter.It is also similar to another species from Guizhou Province, W. pseudoshi Ma, 2016, in chaetotaxy of Th.III and Abd.I−II, but the colour pattern and chaetotaxy of Abd.III−IV are not the same.The differences between the three species are great, as shown in Table 3.

Etymology
Named after Ms Hongdan Tan, who collected the specimens.

Description
MeasureMent.Body length up to 1.5 mm.
Colour.Ground colour pale yellow.Eyepatches dark blue.Antennae and legs almost wholly blue pigmented.Lateral side of Th.II and head behind eyepatches with blue pigment.Blue pigment present on most part of dorsum from Th. III to Abd.V (Figs 8A-8C).
sCales.Hyaline, spinulate type, leaf-like and present on Ant.I−II, dorsal side of head and terga, coxa to tibiotarsus, anterior face of ventral tube and ventral side of manubrium (Fig. 10I).

Remarks
The new species is most similar to the Chinese species W. variabilis Ma, 2016 in colour pattern and scale type, but Abd.I−IV with 3, 3, 1 and 7 central mac in the former respectively, but 7−8, 5, 2, 10−13 central mac in the latter.It is also similar to the species W. sexachaeta sp.nov. in chaetotaxy, but their colour patterns are different.The differences between the three species are shown in Table 4.

Discussion
Scale morphology is a major character in defining species of the genus Willowsia and it was divided into four types (Zhang et al. 2011): spinulate type, short rib type, long basal rib type and uninterrupted type.Among 20 Chinese species of the genus, nine species have scales of the spinulate type and they were described or reported only from the Southwest of China, including Guangxi, Guizhou, Tibet and Yunnan provinces.Ten species with the long basal rib type and one species with the short rib type were from other provinces except the Southwest of China.No species with the uninterrupted scale type have been found in China.

Colour.
Ground colour pale yellow.Antennae with scattered blue pigment, especially distal part of each segment.Eyepatches dark blue.Longitudinal stripe present from eyepatch to Th. III along lateral side (Figs 1A-1B).

Table 1
(continued on next page).Main differences between Chinese species of the genus Willowsia Shoebotham, 1917.

Table 3 .
Ma, 2016, 1873)illowsia christianseni sp.nov., W. nigromaculata(Lubbock, 1873)and W. pseudoshiMa, 2016.DiagnosisAntennae and legs almost wholly blue pigmented and blue pigment present on most part of dorsum from Th. III to Abd.V; Abd.I with 3 mac; Abd.II with 3 central mac; Abd.III with 3 central and 3 lateral mac; Scales spinulate type and present on Ant.I−II, dorsal side of head and terga, coxa to tibiotarsus, anterior face of ventral tube and ventral side of manubrium.