Heteroisotoma heteronomica, Jie, Ding, Potapov, Mikhail & Sokolova, Elena, 2011

Jie, Ding, Potapov, Mikhail & Sokolova, Elena, 2011, Further study on the labial palp in the Isotomidae (Collembola) with reference to the genus Heteroisotoma Stach, Zootaxa 2991, pp. 49-61 : 55-58

Heteroisotoma heteronomica sp. nov.

Figs 26–35

Type material. Holotype: subadult male, Russia (Far East), Khabarovsky Krai (northern part), Ezop Range, Bureinskaya Rassoshina River, mountain larch taiga, ~ 900-1000 m alt., leg. A. Brinev & A. Polyakov, moss and lichens (extracted with paradichlorinebenzol), July 2006.

Paratypes: 1 subadult male and 1 juvenile specimen, same data as for holotype (deposited in MSPU).

Description. Body size of subadult males 1.35 mm. Body shape as common for the subfamily, head large. Abd. V and VI separated, with a fold and clear break in setal covering. White. Integument smooth.

No ocelli. PAO 1.8–2.0 as long as claw III, subdivided to lobes, upper and lower ends narrowed, lower tip bilobed ( Fig. 34 ). Ant. I on ventral side with 2 long sensilla and 2–3 short ones in apical position. Ant. III organ normal, with a pair of blunt rods in a groove. Ant. IV without subapical pin-seta, with curved subapical sensillum and big subapical organite ( Fig. 32 ). Organite tulip-shaped (probable artefact, see the description of previous species). Labrum with 4/554 slender setae, apical edge with 4 sharp ridges and a composite ventral ciliation. Central part of frontoclypeal field with about seven setae. Maxillary outer lobe with trifurcate palp and 4 sublobal setae. Labial palp with all apical papillae (A–E) and 16 guards (including e7), 4 proximal setae ( Fig. 33 ). Lateral process (l.p.) finger-like, medial process of the same shape, between papilla A and first proximal seta. Papillae B and D with well developed additional processes (B' and D' on Fig. 33 ). Basal fields of labium with 4 median and 5 lateral setae. Head with 4–5+4–5 postlabial setae along ventral line. Mandibles normal. Maxillae with 3-toothed capitulum and 6 unmodified lamellae, without long denticles, not projecting beyond tip of capitulum.

Tibiotarsi with 8 acuminate distal setae. Claws as common for the genus, with one inner and two lateral teeth, unguiculus with wide lamellae and inner tooth. Lower subcoxa of Leg I with 2 outer setae. Ventral tube with 9–10 + 9–10 anterior, 5+5 lateral and about 12 posterior setae. Retinaculum with 4+4 teeth and 5–6 setae. No ventral setae on thorax. Ventroapical thickening multispinose, with 3–5 teeth ( Fig. 31 ). Ventroapical area with a pair of spines swollen at basal half ( Fig. 31 ). Dens with many anterior and 11–12 posterior setae. With one row of large setae running along lateral side ( Fig. 35 ). 7–8 setae of inner row of dens modified to spines, swollen at base and elongated in distal part (spines and lateral setae not included in posterior group of setae here). Mucro short, tridentate, no seta.

Macrochaetotaxy as common for the genus: 3,3, 3,3 in number on Abd. I–IV. On posterior half of abdomen macrosetae slightly serrated (under high magnification). Macrosetae more uniform in shape then in H. sinorossica sp. nov., as common for the genus ( Figs 27–30 ). Medial macrosetae of Th. II and III slightly thinner than other macrosetae of body. Macrosetae of Abd. V 1.2–1.25 as long as tergite length. Sensillary chaetotaxy complex. Macrosensilla as 5,2/2,4,4,4,6(8) in number. Size and shape of sensilla shown in Fig. 26 . Sensilla of accp-group on Th. II and Abd. I absent ( Fig. 27 ). Abd. V with 2 as-s (as1, as2) and 4 accp-s of which 2 long and thin (accp1, accp2) and 2 short (accp3, accp4). Besides, accp-row with an additional long and thin sensillum located anterior and laterally to accp-1 sensillum ( Fig. 30 , notated as "s?"). Most number of common setae and mesosetae on dorsal side of Abd. II–VI represent thin and tubular "pseudosensilla" giving an impression of dense cover (these pseudosensilla notated as s' on figure). Accp-5 sensilla (common for the subfamily) possibly also present but masked by covering of numerous pseudosensilla. Microsensilla big, 1,1/1,1,1, located in front of p-row on Abd I, II and in p-row on Abd. III. Number of p-setae between accp-s and ms on Abd. II–IV as: 4s1s1s, 4s1s1s1ms0s, 1s2s1s0s (varies slightly).

Remarks. H. heteronomica sp. nov. shares the presence of spines on inner side of dens only with H. sinorossica sp. nov. Multispinous manubrial thickening, blindness, pseudosensillar covering, and shape of PAO also indicate their similarity. The new species differs from H. sinorossica sp. nov. in having fewer sensilla on Th. III and Abd. I, in the shape of the body sensilla on abdomen, and the number of spines in the ventroapical group of manubrium (1+1 versus 2+2). The formal difference between the species in number of setae and length ratios of body parts needs verification since they may be a result of few individuals of H. heteronomica sp. nov. available for the study. Among Holarctic isotomids, these two species are morphologically unique because of the combination of blindness with a spined dens.

Etymology. The species has unequal number of sensilla on body tergites and, thus, shows heteronomic sensillar chaetotaxy.

Distribution and ecology. The species is known only from the type locality where it was already listed as Heteroisotoma sp. nov. ( Potapov & Polyakov 2007).

Figures

FIGURES 26 – 30. Heteroisotoma heteronomica sp. nov.: 26, macrosetae, sensillae and p-row of setae on body tergites (area of location of pseudosensilla marked with dotted line); 27, 28, dorsal chaetotaxy of Abd. I (27) and II (28); 29, macrosetae of body tergites; 30, chaetotaxy of dorsal side of Abd. IV – VI; s, accp, as: macrosensillum, ms: microsensillum, s': pseudosensillum.

FIGURES 31 – 36. Heteroisotoma heteronomica sp. nov. (31 – 35) and Semicerura goryshini (36): 31, dorsal side of manubrium and proximal part of dens (not all spines shown on dens); 32, tip of antenna; 33, labial palp (partly, guards not shown); 34, postantennal organ, lateral view; 35, proximal part of dens; 36, labial palp (area associated with medial process marked); sm: subapical microsensillum, org: subapical organite, B', D': additional processes, m. p.: medial process.