Isotominella Delamare Deboutteville, 1948

Potapov, Mikhail B., Janion-Scheepers, Charlene & Deharveng, Louis, 2020, Taxonomy of the Cryptopygus complex. III. The revision of South African species of Cryptopygus and Isotominella (Collembola, Isotomidae), ZooKeys 945, pp. 99-127 : 99

Isotominella Delamare Deboutteville, 1948

Type species.

Isotominella geophila Delamare Deboutteville, 1948

Diagnosis.

The genus belongs to the Cryptopygus complex. Ocelli absent. Medial s-chaetae in posterior position from Th. II to Abd. IV. Number of s-chaetae 3,3/2,2,2,2,3. Foil chaetae at the end of abdomen absent.

Discussion.

The genus Isotominella was described from Ivory Coast and was subsequently given a detailed diagnosis by Jordana et al. (2009) based on material of I. geophila from Algeria. The taxon was considered a member of the Cryptopygus complex and was said to differ from related genera mainly by the crenulation, which is developed only in the proximal half of the dens. According to Jordana et al. (2009), in other genera of the complex this crenulation is either absent (i.e., dens is “smooth”), or extends further along the posterior side of dens, as in Hemisotoma Bagnall, 1949.

In our view, the crenulation is a flexible character within the genera of the Cryptopygus complex and depends on the length of furca, which can vary highly within a large genus, e.g., in Cryptopygus s. str., and particularly, among its representatives in South Africa (Figs 14 , 30 , 35 , 43 ). Two species of the genus Isotominella , I. geophila and I. laterochaeta sp. nov. share a remarkable s-chaetotaxy, particularly, the posterior position of medial s-chaetae on body tergites, a reduced s-formula (3,3/2,2,2,2,3), and differentiation of s-chaetae on Abd. V with two long dorsal and one short lateral s-chaetae. The mouth parts of the two species are uncommon: the terminal ‘sensilla’ of papilla A and B are rod-like, the number of basolateral chaetae of labium are increased, the labrum has two prelabral chaetae, the number of sublobal hairs of maxillary outer lobe is reduced (three in the new species and two in I. geophila ), and the maxillary head is modified. The presence of 7-9 basolateral chaetae on the labium (vs. commonly five as determined by Fjellberg 1999) in I. laterochaeta sp. nov. have not been recorded so far for Isotomidae . This remarkable feature is less pronounced in I. geophila in which this number is variable (five or six). Six basolateral chaetae on the labium were found in the genus Pauropygus ( Potapov et al. 2013) in P. projectus Potapov et al., 2013, P. caussaneli , P. pacificus Potapov et al., 2013, which also shows the posterior position of the s-chaetae on tergites. The two genera share other important characters and are probably closely related ( Potapov et al. 2013). Labral chaetae are normally pressed to the labrum in Isotomidae , while they are projected forward in the new species (the character is unclear for I. geophila ). Isotominella also resembles the blind genera Cylindropygus Deharveng et al., 2005 (Europe) and Dagamaea Yosii, 1965 (East Asia and North America) but reliably differs by the posterior (vs. mid-tergal) position of the s-chaetae on the body tergites. A table to compare all the genera of the complex Cryptopygus is given by Jordana et al. (2009).

Figures

Figures 6 - 14. C. bulbus sp. nov. 6 Abd. IV and fused Abd. V and VI 7 labrum, lateral view 8 ocelli, PAO and Ant. I 9, 10 apical part of Ant. IV, different views 11 tibiotarsus and claw of Leg III in adult male 12 ventral tube, ventral view 13 furcal area, ventral view 14 furca, lateral view. Abbreviations: ab apical bulb, org organit, sms subapical ms-chaeta, bms basal ms-chaeta, ss s-chaeta.

Figures 26 - 31. C. postantennalis sp. nov. 26 macrochaetotaxy and s-ms-pattern 27 PAO and eye area 28 Ant. I 29 apical part of Ant. IV 30 dens, lateral view 31 Abd. IV and V. Abbreviations: org organit, sms subapical ms-chaeta, ss s-chaeta, bms basal ms-chaeta, msms-chaeta.

Figures 32 - 36. C. inflatus sp. nov. 32 macrochaetotaxy and s-ms-pattern 33 Abd. IV and fused Abd. V and VI 34 Ant. I 35 dens, lateral view 36 ocelli and PAO. Abbreviations: ss s-chaeta, bms basal ms-chaeta, msms-chaeta.

Figures 42 - 46. C. longisensillus sp. nov. 42 macrochaetotaxy and s-ms-pattern 43, 44 dens, lateral (43) and anterior (44) views 45 Abd. IV and fused Abd. V and VI 46 tibiotarsus and claw of Leg III. Abbreviations: ss s-chaeta, msms-chaeta.