Cave-dwelling Coecobrya from southern China with a survey of clypeal chaetae in Entomobryoidea (Collembola)

Abstract. Four new species of the genus Coecobrya, C. gejianbangi sp. nov., C. annulata sp. nov., C. ciliata sp. nov., and C. oculata sp. nov., are described from Guangxi caves as the representative of the genus in China. Coecobrya oculata sp. nov. of the boneti-group has 1+1 eyes and a serrate outer edge of the unguiculus. The other three species, devoid of eyes and with a tiny outer tooth on the unguiculus, are assigned here to the tenebricosa-group, assuming that the large tooth on the unguiculus is transformed into a tiny one in cave-obligate species. Clypeal chaetae in Entomobryoidea are systematically surveyed for the fi rst time, and are found to be well diversifi ed at species level. They have a potential taxonomical value in discriminating taxa of morphologically conserved groups.


Introduction
The taxonomical history and diagnosis of the genus Coecobrya Yosii, 1956 have been recently reviewed by Zhang et al. (2009).All species of the genus have polymacrochaetotic chaetotaxy, no labral papillae, inverted intrusion on labral margin U-shaped, chaetae mel of labium always smooth, reduced eye number (0 to 3 on each side), pigment reduced or absent, antennal apical bulb absent, falcate mucro with a basal spine, and scales and dental spines absent.Later, Zhang et al. (2011a) divided the genus into tenebricosa-and boneti-groups, blind and with a large outer tooth on unguiculus in the former and eyed and with the outer edge of unguiculus smooth or serrate in the latter.

Results
The following characters are shared by the four species included in this paper and are not repeated in the descriptions: smooth spine-like mic at base of antennae (3 dorsal, 3 (2 in C. oculata) ventral on Ant.I, 1 internal, 1 external and 1 ventral on Ant.II); Ant.IV apical bulb absent; labral papillae absent, inverted intrusion on labral margin U-shaped; prelabral and labral chaetae 4/5, 5, 4, all smooth; fi ve chaetae of the fi rst row of labrum subequal (Fig. 8A); subapical chaeta of maxillary outer lobe slightly larger than the apical one; 3 smooth sublobal hairs on maxillary outer lobe; tip of lateral process of labial palp reaching beyond apex of labial papilla; labial chaetae mel 1 l 2 always smooth; inner outstanding tibiotarsal mac 1-2, located at about 0.33 distance from base, ciliate and tapered; all tenent hairs pointed, subequal to unguiculus in length; tenaculum with 4 + 4 teeth and one large striate chaeta; manubrium without smooth or modifi ed chaetae; mucro falcate with long basal spine, nearly reaching the tip of the apical tooth.

Etymology
Named after Mr. Jianbang Ge, who provided help for our trip in the Mulun Natural Reserve.

Paratypes
CHINA: 2 ♀♀ on slides and 5 ♀♀ in alcohol, same data as holotype.One paratype deposited in NJAU and others in MNHN.

Description
Body length up to 4.2 mm.Body colour white (Fig. 1A).

Paratypes
CHINA: 2 ♀♀ on slides and 4 ♀♀ in alcohol, same data as holotype.One paratype deposited in NJAU and others in MNHN.

Description
Body length up to 3.0 mm.Body colour white or with weak orange pigments (Fig. 1B).

Ecology
Cave-restricted species with troglomorphic characters (long antennae, slightly modifi ed claw, large size).

Remarks
Coecobrya annulata sp.nov. is characterized by annulated Ant.IV, two paddle-like internal S-chaetae of Ant.III organ, tiny mic r, X, X 2 and X 4 on the ventral side of head, 9 smooth clypeal chaetae, an outer tiny tooth on unguiculus (sometimes inconspicuous), 2+2 lateral mac on Abd.III, 6+6 central and 8+8 lateral mac on Abd.IV.It is also the only species having ms on Abd.III among Chinese cave Coecobrya species.It is closest to C. oculata sp.nov.from which it differs in anophthalmy, smooth clypeal chaetae, chaetae on the ventral side of head, "smooth" inner differentiated tibiotarsal chaetae, ventral tube and dorsal chaetotaxy (Table 1).

Description
Body length up to 1.35 mm.Ground colour pale yellow in alcohol (Fig. 1C).

Remarks
Ciliate chaetae H 1-4 on the ventral side of head in C. ciliata sp.nov.are observed in Coecobrya for the second time since C. draconis.Small size, 15 ciliate clypeal chaetae, long smooth straight chaetae on antennae, elongate unguis, truncate or swollen unguiculus, tiny outer tooth on unguiculus (sometimes inconspicuous), and 5+5 lateral mac on Abd.IV are also characteristic.It is closest to C. draconis but differs from it in long smooth straight chaetae on antennae and chaetotaxy of Abd.IV (Table 1).

Description
Body length up to 1.38 mm.Body colour white (Fig. 1D).

Remarks
Coecobrya oculata sp.nov. is characterized by small size, 1+1 eyes, ciliate chaetae R, H 1 , H 2 , X, X 2 and X 4 on the ventral side of head, serrate outer edge of unguiculus, absence of ms on Abd.III and 4+4 central mac on Abd.IV.See Table 1 for comparison with other Chinese cave species.

Modifi cation of the unguiculus in cave species and redefi nition of the tenebricosa-group
Most blind Coecobrya species have a large outer tooth on unguiculus and can be assigned to the tenebricosa-group (Zhang et al. 2011a).Among the fi ve cave species from China, C. oculata sp.nov.lacks troglomorphic features and is similar to non-cave members of the boneti-group.The four other species exhibit more or less marked troglomorphic traits, e.g., elongated unguis with reduction of inner ungual teeth which is displaced towards unguis base when present in C. gejianbangi sp.nov., C. ciliata sp.nov.and C. draconis, or two paddle-like internal S-chaetae on Ant.III organ in C. annulata sp.nov.Among these four blind species, the outer tooth on unguiculus is extremely tiny or absent (Figs 2F, 4E, 6F) instead of being large in typical species of the tenebricosa-group.A tiny outer tooth of unguiculus is not exceptional in Entomobryidae, and often present in cave Pseudosinella Schäffer, 1897 species (Christiansen 1961).The link between cave life and reduction of unguiculus outer tooth in species of remotely related genera suggest evolutionary convergence of the character under similar selective pressure, though the functional basis of this evolution is obscure.Smooth outer edge in C. draconis might be a further reduction from a tiny tooth.Under the assumption of tiny tooth modifi ed from large one, we place the fi ve blind cave Coecobrya species in the tenebricosa-group, that is re-defi ned for those species devoid of eyes.Size and number of outer teeth on unguiculus are not the key character separating the two groups.
Facial chaetotaxy is highly diversifi ed in the number and arrangement of its chaetae, even in several groups morphologically conserved.Three families have a basic pattern of two chaetae arranged in a row.In lepidocyrtids where tergal chaetotaxy and many characters are quite conserved, number of facial chaetae varies from 2 to 13 in the recorded species.For the species with the same number of facial chaetae, they often have different arrangement and size.For example, both Coecobrya pani Xu, Yu & Zhang, 2012 and Coecobrya gejianbangi sp.nov.have 8 facial chaetae, the former with 2, 2, 2, 2 smooth chaetae arranged in four rows and two chaetae of the third row tiny (Fig. 9F), the latter with 1, 3, 2, 2 ciliate chaetae and two median ones of them much smaller than others (Fig. 9B).
Clypeal chaetae in Entomobryoidea don't exhibit obvious differentiation at the familial level, but are diversifi ed at the species level.It could be a powerful tool to help to discriminate species particularly in morphologically conserved groups, e.g., lepidocyrtids.To easily observe this character in a specimen on slide, it is suggested adjusting the specimen to the proper pose during slide preparation.
Abd. I, mac a2 and a3 on Abd.II, mac a7 on lateral Abd.III, and 9+9 lateral mac on Abd.IV.It is closest to another cave species, C. ciliata sp.nov., but differs from it in labial chaetae, and abdominal chaetotaxy (Table1).