Parisotoma ruseki, Janion-Scheepers & Potapov & Deharveng, 2023

Janion-Scheepers, Charlene, Potapov, Mikhail & Deharveng, Louis, 2023, New and little-known Isotominae (Collembola, Isotomidae) from South Africa, Zootaxa 5346 (3), pp. 337-347 : 338-339

Parisotoma ruseki sp. nov.

Figs 1–10

Material. Holotype female on slide and 10 paratypes (on slide), “RSA10_GVB002”: South Africa, Western Cape, Grootvadersbosch Nature Reserve , 23. Aug. 2010, 33.981402°S, 20.826202°E, C. Janion-Scheepers . Holotype and 3 paratypes in SAMC, 3 paratypes in MNHN; 4 paratypes in MSPU.

Description. Body length up to 1.0 mm. Grey, eye spot black ( Fig. 5 ). Ant.I with 4 s-chaetae ventro-laterally of which 2 long chaeta-like and 2 short (set together in distal part or separately, Fig. 6 ), 3 basal microchaetae, 2 dorsal and 1 ventral. Inner s-chaetae of AO III small. Based on cornea, two ocelli on each side of head, set apart, a large anterior one and a smaller, often hardly visible, posterior one ( Fig. 4 ). Eye spot undivided, the pigmentation often concealing the real number of ocelli in dark specimens ( Fig. 5 ). PAO wide, ca 1.4 as long as internal crest of Claw III. Labral formula 4/554, apical folds sharp. Maxillary outer lobe with 4 sublobal hairs and trifurcate apical palp. Labial palp with 5 papillae (A–E) and incomplete set of guards (15, e7 absent), lateral process normal. Labium with 4 basomedian, 5 basolateral, and 4 proximal chaetae. Number of postlabial chaetae 3+3. Inner mouthparts as usual for the genus, maxillary head unmodified: both lamellae 1 and 6 with two rows of filaments ( Fig. 10 ). Lower subcoxa of leg I with one outer chaeta. Tibiotarsi of all legs with only 7 chaetae in apical whorl. Claw without clear internal teeth, with two minute lateral teeth. Empodial appendage with broad lamella. Ventral tube with 2+2 latero-distal, 3+3 anterior, and 4 posterior chaetae ( Fig. 3 ). Retinaculum with 4+4 teeth and 3 chaetae. Furcal subcoxa with 24–31 chaetae. Manubrial thickening simple. Anterior side of manubrium with numerous chaetae of which 2+2 shorter medial ones in its apical part, as common for the genus. Dens with numerous chaetae on anterior side and 7 chaetae on posterior side (2 basal, 2 median and 3 lateral) ( Figs 8, 9 ). Mucro with 3 teeth.

Ordinary chaetae slightly thickened, as usual for the genus. Axial chaetotaxy for Th.II, III, Abd.I, II with 12– 13+12–13, 10+10, 4–5+4–5, 3–4+3–4 chaetae, respectively. Macrochaetae differentiated, ciliate, on last abdominal segments with about 10 cilia ( Fig. 7 ), on Abd.V 1.2–1.4 times longer than length of tergite. On Th.II–Abd.V, s-chaetae thin, well different from common chaetae, sensillary chaetotaxy ( Figs 1, 2 ) as: 2al+4accp, 1al+4accp / 4 accp, 4 accp, 4 accp, 1 am+4 accp, 2 am+5 accp. From Th.II to Abd.III, s-chaetae accp4 and accp5 missing on each side of segment, and 2 s-chaetae (accp4 and accp6) missing on Abd.IV. On Th.II–Abd.III, ms-chaetae as 1,1/1,0,1. On Abd.III, ms-chaetae large, as long as s-chaeta ( Fig. 1 ). Number of common chaetae in p-row between s-chaetae and ms-chaetae: 2s1s1s3s (Abd.I), 2– 2.5s 1s1s3s (Abd.II), 2–3s1s1s2ms1s (Abd.III), 1– 0.5s 1s1s2(s) (Abd.IV) ( Figs 1, 2 ). Males not seen.

Distribution. The new species is currently known only from the type locality, which is in the faunistically specific inner area of Western Cape.

Remarks. The strongly reduced s-chaetae chaetotaxy is shared with only P. sexsetosa Potapov, Janion & Deharveng, 2011 from which the new species differs by 7 (vs 6) posterior chaetae on dens and s6 on Abd.IV and e 7 in labial palp missing. The absence of s6 on Abd.IV was previously unknown in the genus. Chaetae of posterior side of dens (“2 median + 3 lateral”) are as in Holarctic species. The “2 + 3” chaetae on the dens and the absence of lateral s6-chaetae on Abd.IV sharply define this new species in South Africa. Formally, P. ruseki sp. nov. can be compared with P. trichaetosa (Martynova in Martynova et al. 1977) (Palaearctic) which has nearly the same number of s-chaetae on body. Parisotoma trichaetosa differs by four teeth on the mucro, the presence of ms on Abd.II and other essential characters.

Name derivation. The species is dedicated to our Czech colleague Josef Rusek (1938–2022), who contributed immensely to the taxonomy of the genus Parisotoma .

Figures

FIGURES 1–10. Parisotoma ruseki sp. nov.: 1–2, s- and ms-chaetae on Abd. II–V (1) and Th.II–Abd.II (2); 3, ventral tube, lateral view; 4, ommatidia and PAO; 5, pigmentation of eye spot poorly displaying real number of ommatidia; 6, s and bms on Ant.I; 7, macrochaeta on Abd.V; 8–9, dens, posterior (8) and lateral (9) views; 10, maxillary head with more detailed lamellae 1 and 6: s and ms—s- and ms-chaetae, bms—basal microchaeta.