Thalassaphorura Bagnall, 1949

Sun, Xin, Chen, Jian-Xiu & Deharveng, Louis, 2010, Six new species of Thalassaphorura (Collembola, Onychiuridae) from southern China, with a key to world species of the genus, Zootaxa 2627, pp. 20-38 : 24-25

Thalassaphorura Bagnall, 1949

Type species: Onychiurus thalassophilus Bagnall, 1937

Diagnosis. (Pseudocelli and chaetotaxic characters should be observed in adult). Postantennal organ oval, with numerous simple vesicles perpendicular to the long axis; antennal basis more or less indicated; clubs of AIIIO smooth, ribbed or granulated; Ant. IV with S-chaetae differentiated or not, ms close to the second row of chaetae, and no bulb on Ant. IV; labral chaetae formula 4/1,4,2; labium of A, AC or ABC type; no multiplication of dorsal pseudocelli, 3 (rarely 4 or 2) pseudocelli in the antenno-basal group, 3–4 (rarely 2 or 5) pseudocelli per half tergite on Abd. IV, 3 (rarely 4 or 2) pseudocelli per half tergite on Abd. V (2–3 in a postero-internal group, one in a postero-lateral group); chaeta d0 on head present (but given as absent in T. jailolonis by Yoshii & Suhardjono (1992)); Th. I usually with pseudocelli; Abd. VI with one or two axial chaetae (a0 or m0, or both); anal spines present or absent; tibiotarsus with 7 or 9 chaetae in distal whorl, no clavate tenent hairs; furcal rudiment as a finely granulated area with 4 small chaetae in two rows posteriorly.

Discussion. The diagnosis given above is derived from Weiner (1996), Pomorski (1998) and Yan et al. (2006). The presence of 9 chaetae in the distal whorl of tibiotarsi was considered a generic character by these authors; in our material two new species have only 7 chaetae in the distal row of tibiotarsus, but exhibit otherwise all other characters of the genus; we consider that they belong to Thalassaphorura , and we modified the generic diagnosis accordingly.

Species have been assigned to Thalassaphorura according to the weblist of Bellinger et al. (2010), partly set up upon personal communications of Pomorski. Actually, the furcal area and other potentially diagnostic characters of the genus (labrum and labium chaetotaxy, d0 on head, chaetotaxy of distal whorl of tibiotarsus) are unknown in many cases, and generic assignation mostly relies on similarities based on sets of nondiagnostic characters.

Remarks on parthenogenesis in Thalassaphorura . After Chernova et al. (2010), Onychiuridae sensu lato have the largest number of parthenogenetic species among Collembola (10 % of the total number of species of the family). Three species of Thalassaphorura are given as parthenogenetic in the literature ( encarpata after Pomorski (1998) and Chernova et al. (2010); orientalis , after Stach (1964); petaloides after Rusek (1981)). In our material two of the six new species described here are only known by females and are likely parthenogenetic ( T. grandis and T. pomorskii ), rising the total number of parthenogenetic species to five in the genus Thalassaphorura (14 % of its species), the highest number and proportion recorded among Onychiuridae .