Isotomiella delamarei Barra, 1968

Kováč, Ľubomír & Palacios-Vargas, José G., 2008, Redescription of Isotomiella alulu and I. delamarei (Collembola: Isotomidae) with notes on the systematics of the genus and new records from the Neotropics, Zootaxa 1825, pp. 1-17 : 6-8

Isotomiella delamarei Barra, 1968

Figs 8–11

Diagnosis. Body length 0.9–1.0 mm. Ventral side of head with integumentary channels. Ant. IV with 3 dorsointernal and 5 dorso-external subcylindrical sensilla in addition to 6 ovoid ones. Posterior margin of head without ciliated setae. Axial setae pattern 18,12/6,6(8),8,8 by half-tergum from Th. II to Abd. IV. Sensillar pattern 32/00135 by half-tergum from Th. II to Abd. V+VI. Sensillum spl on Abd. V+VI 1.3 times of the length of unguis III. Ti. III with apical setae not thickened. Subcoxae furcalis anterior/posterior with 5–9/6–8 setae; manubrium with 2+2 ventro-apical setae; dens with 10–12 ventral and 4 dorsal setae; mucro strong, bidentate.

Redescription. Body length 0.9–1.0 mm (adult females). Colour white, habitus short and thick, similar to I. alulu and I. nummulifer . Integument of Abd. IV–VI dorsally without craters, with primary granules only. Integumentary channels limited to the ventral side of head. Pseudopora indistinct.

Head. Labral setae pattern 4/554. Labrum with 4 anterior spinules, 2 antero-lateral setae strongly thickened, chitinised and blunt. Axial seta of the second row neither thickened or sclerotized, other 6 labral setae of two distal rows moderately thickened, sclerotized and acuminate. External lobe of maxilla with bifurcate palp, without ciliated setae, and with 4 sublobal setae. Antennae (0.16 mm) 5.5 times shorter than body, shorter than head (0.19 mm). Length of Ant. I, II, III and IV as 24, 37, 40 and 59 μm. Ovoid sensilla S1-S6 of Ant. IV subequal (7 μm; Fig. 8 ). Supplementary sensilla of Ant. IV subcylindrical, 3 dorso-internal and 7 dorso-external of which the one located at 1/2 the length of the segment clearly thicker than others. Ant. III organ with 2 small sensory rods, 3 short guard sensilla in position 1, 4 and 5 and an additional microsensillum s´. Ant. II with sensillum s´. Ant. I with 16–17 smooth ordinary setae, 2 basal microsetae and 2 unequal ventral sensilla S (8 μm) and s (4 μm). Ciliated setae on posterior margin of head absent.

Terga. Axial setae pattern from Th. II to Abd. IV: 18,12/6,6(8),8,8. Macrosetae rather long, weakly ciliated, 1,1/3,3,3,4 by half-tergum from Th. II to Abd. IV. On Th. II to Abd. III only smooth mesosetae present. On Abd. I macrosetae of the different length: Md 18 μm, Mdl 24 μm and Ml 30 μm; length of mesosetae of the posterior row 17–18 μm. On ventro-lateral part of Abd.II several setae of anterior rows absent. Abd.IV bearing ciliated setae in the posterior row. On Abd. V+VI macro- and mesosetae weakly ciliated, others smooth. Unpaired setae of Abd.V+VI: a0 strongly ciliated mesoseta (17 μm), m0 smooth macroseta (33 μm) and p0 strongly ciliated mesoseta (24 μm); the distance between m0 and p0 very short (4 μm). Sensillar formula of the minor - type: 32/00135 (ms: 10/00000; s: 22/00135) by half-tergum from Th. II to Abd.V+VI. Sensillum sl3 on Th. II in normal position (not migrated towards anapleurite). Sensillum spl of Abd.V long (28 μm), with thick basal part gradually narrowing towards its apex; sensilla sa, spi, spe shorter than sensilla of Abd.IV (9– 10 μm and 10–13 μm, respectively); sensillum sv short (8 μm; Fig. 9 ). Ventral anal valves each with 6 posterior setae of which one medial is smooth macroseta, others strongly ciliated mesosetae. Dorsal anal valve with 7 posterior setae of which p1 is weakly ciliated macroseta, others strongly ciliated mesosetae (incl. p0).

Appendages. Setae numbers from leg I to III (ciliated setae in parenthesis): anapleura 1(1), 2(1–2), 2; katapleura 1(1), 5(4), 6(1–2); coxae 2, 10(2), 12(2); trochantera 10, 10, 10; femora 22, 23, 24 and tibiotarsi 26, 28, 30. Proximal whorl of Ti. I with 7 setae. On Ti. III no tenent hairs or thickened apical setae ( Fig. 10 ). No spine-like setae on femora, tibiotarsi, coxae or pleura. Unguis and unguiculus (22 and 11 µm) of normal shape (not elongated); untoothed. Tubus ventralis with 5+5 distal, 3+3 anterior and 2+2 posterior setae. Retinaculum with 4+4 teeth and 1 seta on the rami. Subcoxae furcalis anterior with 5–9 setae (0–1 ciliated), subcoxae furcalis posterior with 6–8 setae (0–3 ciliated). Furcula short (0.15 mm) not reaching tubus ventralis. All setae on manubrium and dentes smooth. Manubrium (58 μm) with 2+2 ventro-distal setae placed in two longitudinal rows, ventro-proximal and lateral setae absent ( Fig. 11 ). Dorsal setae on manubrium and dentes thin, ventral setae thicker. Dens short (80 μm), with 4 dorsal setae and 10–12 ventral setae of which distal strong one reaching the tip of mucro distinctly longer (20 μm) than the anteapical seta (8 μm). Mucro rather long (11 μm), bidentate with well developed apical tooth. Basal hooks of dens very strong.

Only females known.

Type material. Holotype (female) on slide (IPA9-AN4), Gabon, Ipassa Plateau, primary forest, litter, 27.vi.1966 J.A. Barra lgt.; 3 paratypes on slides (IPA1- AVCT 3, IPA5-E4. IPA7-VM6), ibid. 7.v., 7.vi. and 17.vi.1966. Type material kept in the Laboratoire de Zoologie, Université Louis Pasteur, Strasbourg, France.

Other material. 1 specimen on slide (IPA7-VM6), ibid., 17.6.1966.

Discussion. By the presence of 2+2 ventral manubrial setae and 2 mucronal teeth I. delamarei Barra, 1968 is related to I. spinifer Deharveng & Oliveira, 1990 , I. nummulifer Deharveng & Oliveira, 1990 , Isotomiella alulu Christiansen & Bellinger, 1992 and I. fellina Mendonça & Fernandes, 2003 . Differential characters of the redescribed species and the closely related ones are listed in Table 1.

The principal difference between I. delamarei and above mentioned species is the number of sensilla on segments Th.II–Abd.V (3,2/0,0,1.3.5) that clearly indicates its phylogenetic affinity to I. minor species group.

Figures

FIGURES 8 – 11. Isotomiella delamarei Barra, 1968: 8, right antenna in dorsal view with position of ventral sensilla on Ant. I.; 9, Abd. IV – VI (dorso-lateral view) with subcoxae furcalis anterior and posterior; 10, tibiotarsus, unguis and unguiculus of leg III; 11, furcula, ventro-lateral view (dens and mucro on the right side from the lateral view).