Mastigoceras Handschin, 1924

Rodrigues, Iandra Vitória Bezerra, de Souza, Paolla Gabryelle Cavalcante, Nunes, Rudy Camilo, Nunes Godeiro, Nerivânia & Bellini, Bruno Cavalcante, 2024, A century later: a new species of Mastigoceras Handschin, 1924 (Collembola, Orchesellidae), with morphological and systematic updates on the genus, ZooKeys 1217, pp. 79-100 : 79-100

Genus Mastigoceras Handschin, 1924

Type species.

Mastigoceras camponoti Handschin, 1924 .

Diagnosis.

Fusiform small hyaline ciliate scales, without ribs, present at least in dorso-anterior Th. III – Abd. III, present or absent on dorsal head, Th. II, and Abd. IV; antennae, legs, ventral tube, tenaculum and furca scaleless. Body also densely covered by secondary ciliate mic; dorsal macrochaetotaxy reduced. Antennae very long, 2–4 × the body length; antennae with five segments, Ant. I subdivided, Ant. II stiff or weakly annulated, Ant. III – IV longer than other segments, annulated and whip-like; Ant. IV apical bulb absent. Eyes 8 + 8, PAO present. Tergal sensilla and microsensilla formulae of Th. II – Abd. V as 1, 1 | 0, 3, 3, +, 9 and 1, 0 | 1, 0, 1, 0, 0, respectively. Th. II anterior (a) series, including the collar, with up to 17 mac. Abd. IV less than 1.5 × the length of Abd. III in the midline. Abd. VI of males short and rounded; of females long and conical. Trochanteral organ variably developed. Tenaculum without chaetae. Manubrium dorsally with one or two bothriotrichum-like chaetae; dens crenulate, without spines; mucro bidentate with the basal spine (adapted and updated from Handschin 1924; Cassagnau 1963; Mari-Mutt 1978; Cassagnau and Oliveira 1992).

Remarks.

Our updated diagnosis adds the tergal sensilla and microsensilla formulae to Mastigoceras , details on the distribution of body scales, and outlines the presence of the PAO. This last feature was overlooked in the original description of M. camponoti ( Handschin 1924) , along with its subsequent redescriptions ( Cassagnau 1963; Mari-Mutt 1978; Cassagnau and Oliveira 1992). However, we could confirm the presence of this structure in a specimen of M. camponoti from the type locality (Mariana municipality, south of Minas Gerais state, Brazil), as well as in Mastigoceras handschini sp. nov. In Mari-Mutt (1978: 46, fig. 8), there is a SEM picture of the right eyepatch of M. camponoti showing the PAO as a small cuticle fold in front of A eye lens.

The overall morphology of Mastigoceras species resembles other Entomobryoidea in several aspects. These shared features include the presence of a trochanteral organ and post-ocular bothriotricha, dorsal body covered with abundant secondary ciliate mic, alongside some larger ciliate mes and blunt mac, Abd. II – IV bothriotricha formula 2, 3, 2, and dens crenulate with a bidentate mucro holding the basal spine ( Soto-Adames et al. 2008). Even so, the disposition of Abd. IV bothriotricha in Mastigoceras is quite unusual, being posteriorly displaced (see Figs 4 E , 6 F ; Cassagnau and Oliveira 1992: 30, fig. 2 b). This condition does not relate with other Orchesellidae or Entomobryoidea ( Szeptycki 1979; Zhang et al. 2019; Nunes et al. 2020) and makes it difficult to understand the homology of the lateral chaetae on the same tergite.

Figures

Figure 4. Mastigoceras handschini sp. nov. overall morphology A Ant. Ia apex, arrows point to small smooth mic at the apex B head, showing frontal eyes and PAO C Abd. I with modified fan-shaped p 6? and ms microsensillum D Abd. III anteriorly (Abd. II tergum covering the most anterior region of Abd. III), with a transversal line of fusiform scales, both Abd. II and III with plentiful secondary mic E Abd. IV distal region, showing T 2 and T 4 bothriotricha, T 3 finger-like chaeta and ps sensillum F Dorsal (anterior) manubrium, arrow points to a bothriotrichum-like chaeta.

Figure 6. Mastigoceras handschini sp. nov. dorsal trunk chaetotaxy, left side A Th. II B Th. III C Abd. I, arrow indicates a small fan-shaped modified chaeta D Abd. II E Abd. III F Abd. IV, arrow indices a finger-shaped ciliate chaeta (T 3) between the bothriotricha, dotted mac alveoli represent different positions to the same chaetae G Abd. V, arrows pointing to lateral mes which can also be bothriotricha-like chaetae H transversal row of anterior scales on Abd. II. Other primary chaetae may be present in terga as mic, but are obscured by the dense microchaetal covering of the specimens.