Ceratophysella species from mushrooms in China (Collembola, Hypogastruridae)

Abstract Four species of the genus Ceratophysella living on mushrooms are reported from China, including a new species, Ceratophysellaskarzynskii Weiner & Sun, sp. n., which is described from alpine mushrooms. The new species belongs to the Ceratophysella group of species with a dorsal chaetotaxy of type B and differs from the other species in a combination of characters. Ceratophysellaskarzynskiisp. n. is distinguished by its small body size (maximum length 1.09 mm), number of peg-like s-chaetae (30–32) in the ventral sensory file, the trilobed apical vesicle of antennal segment IV, five modified chaetae on dens, and serrated dorsal chaetae. A key to the Chinese species of the genus has been provided.


Introduction
The genus Ceratophysella Börner, 1932 is distributed worldwide, having more than 130 species (Bellinger et al. 1996(Bellinger et al. -2018. The main diagnostic characters for the genus are the pigmented body, 8 + 8 ocelli, body chaetae mostly differentiated into microand macrochaetae, an eversible integumental sac usually present between antennal segments III and IV, the ventral side of antennal segment IV with a sensory file often well-developed of short, erect, curved, and flattened at tips s-chaetae, unguiculus with broad basal lamella, furca well developed, mucro usually boat-like with a spoon-like apex and distinct lamella, and anal spines usually long and curved. Until now, fourteen species of the genus Ceratophysella have been reported from China (Zhao 1992, Shen 1993, Liu et al. 1998, Zhao et al. 1997, Jia et al. 2010. As a common group of Collembola living on mushrooms, species have often caused significant economic damage in China (Wei 2002;Zhu 2012). Within a large collection of the mushroom Collembola in China, three known species, C. communis (Folsom, 1898), C. denticulata (Bagnall, 1941), C. liguladorsi (Lee, 1974), and the new species described here, C. skarzynskii sp. n., are reported in the present paper.

Materials and methods
Specimens were collected by hand using a brush and stored in ethanol; they were then cleared in lactic acid and KOH, and mounted in Marc André II medium. Drawings and measurements were made using a phase contrast microscope LEICA DM2500 equipped with a camera lucida.
Diagnosis. Dorsal chaetotaxy of type B with serrated chaetae. Maximal length 1.09 mm. Antennal segment IV with bi-or trilobed apical vesicle and ventral sensory file with 30-32 peg-like s-chaetae. Dens with seven chaetae, five of them modified.
Head. Ocelli 8 + 8. Postantennal organ 1.5 times as large as single ocellus with four lobes of which the anterior pair is larger than the posterior pair ( Fig. 2C). Accessory boss present (Fig. 2C).
Anal spines as long as inner edge of claw III slightly curved, situated on basal papillae, colourless (Figs 1B, 3C).
Etymology. The species is cordially dedicated to our colleague and friend Dr Dariusz Skarżyński, a prominent Polish specialist in Hypogastruridae, Collembola.
Remarks. The new species belongs to the armata-group of species, group B (Abd. tergum IV with p 1 as macrochaeta) and subgroup B2 (Abd. tergum IV without chaeta p 3 ) (Bourgeois and Cassagnau 1972). Among the species which could belong to this subgroup,C. skarzynskii is most similar to four species: C. denisana (Yosii, 1956), C. empodialis Babenko, 1994(in Babenko et al. 1994), C. longispina (Tullberg, 1876, and C. scotica (Carpenter & Evans, 1899), due to the absence of transformed into spines, spine-like chaetae or spine-like integumentary protuberance on the head or Abd. V. They differ in the shape of the apical vesicle, the number of modified chaetae on the dens, the number of peg-like chaetae in the ventral sensory file on Ant. IV, length of empodial appendage,in the type of dorsal chaetae (serrated or smooth), and in the number of sublobal hairs on maxillary palp (one or two). A comparison of these species is presented in Table 1.

Key to the Chinese species of Ceratophysella
In 2007 Wu and Yin proposed a key to the six species of the genus Ceratophysella known from China. Jia et al. (2010) proposed a list of 14 Chinese species of Ceratophysella. The present key includes 15 species. Some of the species are not sufficiently described, but the available characters given in the descriptions are sufficient to include them in the key. The characters for C. adexilis have been verified on type material, and for C. communis on fresh material from the type locality (Tokyo).