Isotomiella alulu Christiansen & Bellinger, 1992

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 : 2-5

Isotomiella alulu Christiansen & Bellinger, 1992

Figs 1–7

Diagnosis. Body length 0.8–1.0 mm. Integument with distinct craters from Abd.IV to Abd.VI. Ant. IV with 34–42 thin subcylindrical sensilla in addition to 6 ovoid ones. Posterior margin of head with ciliated setae. Axial setae pattern 22,14 (16)/6,6,6,6 by half-tergum from Th. II to Abd. IV. Ventro-lateral area on Abd.II devoid of setae. Sensillar pattern 32/11212 by half-tergum from Th.II to Abd. V+VI; sensillum spl on Abd. V+VI 1.5 times of the length of unguis III. Ti.III with 2 strongly thickened apical spines. Subcoxae furcalis anterior/posterior with 10–12/7 setae; manubrium with two pairs of unequal ventro-distal setae; dens with 17– 19 ventral and 5 dorsal setae. Mucro bidentate.

Redescription. Body length 0.8–1.0 mm (adult females). Colour white, habitus of I. nummulifer Deharveng & Oliveira, 1990 . Integument from Abd. IV to Abd. VI dorsally with many distinct craters ( Fig. 4 ), 1.0– 1.5 times broader than diameter of macrosetae (1.5–5.5 Μm). Anterior abdominal segments with indistinct, or completely absent craters. Secondary granules and integumentary channels absent. Pseudopora distinct on Th. II.–Abd. IV.

Head. Labral setae pattern 4/554. Labrum with 4 anterior spinules, antero-lateral setae weakly thickened, setae in two distal rows (9) slightly thicker than those in proximal one (5). External lobe of maxilla with bifurcate palp, without ciliated setae and with 3 sublobal setae. Antennae (0.2 mm) 3.8–4.2 times shorter than body and apparently longer than head (0.16 mm). Length of Ant. I, II, III and IV as 26, 45, 45 and 85 μm. Ovoid sensilla S1–S6 of Ant. IV subequal (8 μm); numerous supplementary thin sensilla present, 22–27 dorsal and 12–15 ventral ( Figs 1 and 2 ). Ant. III organ with 2 small sensory rods, 3 short guard sensilla in position 1, 4 and 5 and additional sensillum s´. Ant. II with sensillum s´. Ant. I with 15–17 smooth ordinary setae, 2 basal microsetae and 2 unequal ventral sensilla: S (8 μm) and s (5 μm). Posterior margin of head with ciliated setae ( Fig. 3 ), mesosetae p1–p 3 in p-row always ciliated, additional 2–3 setae in pp -row eventually ciliated (usually pp2, pp4 and pp6).

Terga. Axial setae pattern from Th. II to Abd. IV: 22,14(16)/6,6,6,6. Macrosetae long, ciliated, 1,2/2,3,4,4 by half-tergum from Th. II to Abd. IV. Both ciliated and smooth mesosetae present on terga: Th. II and III with 5–7 lateral setae ciliated, others smooth; Abd. I with most setae smooth; Abd. II and III with most dorsal setae ciliated, latero-ventral setae smooth; Abd. IV with most setae smooth, Abd. V+VI with dorsal setae smooth, some lateral setae ciliated. On Abd. II ventro-lateral area devoid of setae. Abd. V+VI with 7 microsetae („mesosetae gl “ after Deharveng & Oliveira 1990). Unpaired setae of Abd.V+VI: a0 microseta (5 μm), m0 and p0 mesosetae (18 μm), all smooth. Mesoseta p2 of Abd.VI slightly shorter than p1 (23 and 26 μm respectively, Fig. 4 ), both smooth or indistinctly ciliated. Sensillar formula of the nummulifer - type: 32/11212 (ms: 12/00000; s: 20/11212) by half-tergum from Th.II to Abd. V+VI. Sensillum sl3 on Th. II has migrated towards the anapleurum. Sensillum spl of Abd. V thick and long (18 μm). All posterior setae on anal valves smooth.

Appendages. Setae numbers from leg I to III (ciliated setae in parenthesis): anapleura 1(1), 2(1), 4(3); katapleura 1(1), 6(3), 7(3); coxae 2, 10(2), 12(2); trochantera 10, 10, 10; femora 20, 24, 26(0–3) and tibiotarsi 28, 28, 31–32. Ti. I with 7 setae in the proximal whorl. Ti. III with 2 strongly thickened apical spines ( Fig. 5 ). No spine-like setae on femora, trochantera or pleura. Unguis and unguiculus (18 and 12 µm) of normal shape (not elongated), untoothed. Tubus ventralis with 4+4 distal, 3+3 anterior and 2+2 posterior setae. Retinaculum with 4+4 teeth and 1 seta on the rami. Subcoxae furcalis anterior with 10–12 setae (6–9 ciliated), subcoxae furcalis posterior with 7 setae (5–7 ciliated, Fig. 6 ). All setae on manubrium and dentes smooth. Manubrium (45 µm) with 2+2 unequal ventro-distal setae placed in transversal row, 2+2 lateral and 19–22 + 19–22 dorsal setae. Ventro-proximal setae on manubrium absent. Dens (125 µm) with 17–19 ventral (distal one distinctly longer) and 5 thin dorsal setae. Mucro (8 µm) bidentate ( Fig. 7 ). Basal hooks of dens normal.

Only females known.

Variability. At the posterior margin of head p1–p3 mesosetae of p -row are always ciliated (sometimes also p5, p6 and p7). In pp -row 2 or 3 setae are ciliated (pp2, pp4 or also pp6). One specimen from Ecuador with dorso-external sensillum in the middle of the Ant.IV clearly thicker than other ordinary dorsal sensilla.

Type material. Holotype (female) on slide Nr. 6738, Hawaii, Oahu Island, Manoa Falls Trail, ohia fern scrub forest, soil, 3.viii.1986, K. Christiansen lgt., 3 paratypes on slides (2 ex. Nr.6743, 1 ex. Nr. 6745) with the same collecting data. Type material kept in the Bishop Museum, Honolulu, Hawaii, U.S.A.

Other material. HAWAII. Oahu island: Aiea Loop Trail, forest in soil and under bark, 4.viii.1986, K. Christiansen lgt. (Nr. 6749a–3 ex., Nr. 6749b–3 ex., Nr. 6754–3 ex.); Haiku Stairs; scrub and grass, 5.viii.1996, K. Christiansen. lgt. (Nr. 6764–4 ex.); Manoa Falls Trail, litter, P. Bellinger lgt., 23.ix.1996 (Nr. 4766–4 ex.); Waahila Ridge Recreational Area (Honolulu), Casuarina grove, soil, 6.viii.1986, K. Christiansen.lgt. (Nr. 6770–4 ex.); Waianae Kai, 7.viii.1996, kukui grove, soil, K. Christiansen lgt. (Nr. 6784–3 ex.).

Kauai island: Hanalei Walley State Conservation Area, dry forest, under bark, 25.vii.1986, K. Christiansen lgt. (Nr. 6728–2 ex.); Kapaa, forest reserve, 26.ix.1980, litter under paper bark tree and moss on hau tree, 26.ix.1980, L.M. Goff lgt. (Nr. 5202–4 ex., Nr. 5207–6 ex.); Kapaa, cane field area, moss on paper bark tree, 26.ix.1980, L.M. Goff lgt. (Nr. 5203–1 ex.).

All specimens from Hawaii are kept on slides and deposited in the Bishop Museum, Honolulu, U.S.A., except slides Nr. 6728 and Nr. 6784 deposited at the Grinnell College, Grinnell, Iowa, U.S.A.

MEXICO. Chiapas, Biological Station Chajul, litter, 20.x.1993. G. Ríos and R. Villavicencio lgt. (1 ex.) Campeche: Actún Guachapil, seeds, guano and fruits, 22.3.1997, A. Ruiz lgt. (2 ex.) Veracruz: Grutas de Atoyac, soil, 6.xii.1981, V. Granados lgt. (1 ex.); Palma Sola, rotten trunk, 5.vi.1976, J. G. Palacios lgt. (1 ex.).

GUATEMALA. Alta Verapaz, tropical rain forest, soil, 1976, G. Kramer lgt. (1 ex.).

NICARAGUA. León, Izapa, soil and leaf litter, 16.vi.1986. J. G. Palacios lgt. (7 ex.).

ECUADOR. Los Tayos (Eastern foothills of S. Andes), seed deposit from oil bird faeces ( Steatornis caripensis ), 1.vii.1976. P. Ashmole lgt. (1 ex.).

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

Ma––ciliated meso-, macrochaeta; mi, me, ma––smooth micro-, meso-, macrochaeta)

Character I. spinifer I. nummulifer I. alulu I. fellina I. delamarei Deharveng & Deharveng & Christiansen & Mendonça & Barra, 1968 Oliveira, 1990 Oliveira, 1990 Bellinger, Fernandes, 1992 2003

Body length (mm) 0.7–0.75 0.5–0.9 0.8–1.0 0.4–0.5 0.9–1.0 I. alulu is closely related to I. nummulifer , differing by the following characters: longer body: 0.9–1.0 mm (0.5–0.9 mm in I. nummulifer ), high number of fine supplementary sensilla on Ant. IV: 34–42 (around 10 in I. nummulifer ), axial setae pattern formula 22,14/6,6,6,6 by half-tergum from Th. II to Abd. IV (22,14/4,4,4,6 in I. nummulifer ), macrosetae formula 1,2/2,3,4,4 by half-tergum from Th. II to Abd. IV (1,1/1,2,4,4 in I. nummulifer ), the ratio of sensillum spl (Abd. V+VI) to GIII: 1.5 (1.0 in I. nummulifer ), 19–22 dorsal setae on manubrium by half side (12–15 in I. nummulifer ), and 17–19 ventral setae on dens (19–24 in I. nummulifer ).

Geographic distribution. From the list of I. alulu localities provided in this paper indicates that the species is not endemic to the Hawaii Islands. Its distributional range is much greater, covering also Central and at least northern part of South America, most-probably majority of the Neotropical biogeographic region. Such an example of affinity of Hawaiian Collembola to the Neotropics is interesting, since Christiansen and Bellinger (1994) pointed out that Hawaiian fauna of Collembola appears to have been recruited primarily from North America and temperate Asia. However, it is also possible that I. alulu has pantropical distribution range similarly as closely related I. nummulifer . The species was cited previously as Isotomiella minor from Nicaragua ( Maes & Palacios-Vargas 1988).

Figures

FIGURES 1 – 7. Isotomiella alulu Christiansen & Bellinger, 1992: 1, Ant. IV and tip of Ant. III, dorsal view (full circle: position of long and narrow sensillum); 2, Ant. IV and tip of Ant. III, ventral view; 3, setal pattern of posterior part of head, dorsal view; 4, Abd. IV-VI, dorso-lateral view; 5, tibiotarsus, unguis and unguiculus of leg III; 6, subcoxae furcalis anterior and posterior; 7, furcula (left side in dorsal, right side in ventral view) and tip of dens with mucro in detail.