Entomobrya nigriventris Stach, 1929

Winkler, Daniel, Sternalski, Jakub, Onodi, Gabor, Szigeti, Nora, Florian, Norbert & Danyi, Laszlo, 2023, Investigation on the true identity of Entomobrya nigriventris Stach, 1929 (Collembola, Entomobryidae) with the description of a new species, ZooKeys 1185, pp. 321-353 : 321

Entomobrya nigriventris Stach, 1929

Figs 7 , 8 , 9

Entomobrya nigriventris Stach, 1929: 302; Bonet 1934: 168 (keyed, diagnosis); Gisin 1944: 77 (keyed); Gisin 1960: 222 (keyed, diagnosis); Stach 1963: 16, 40-41, pl 9 figs 4-6 (keyed, redescribed): Palissa 1964: 204 (keyed, diagnosis); Hornung 1986: 138; Loksa 1987: 79; Jordana 2012: (keyed, diagnosis); Traser et al. 2006; Dányi and Traser 2008: 33; Flórián et al. 2019: 9.

Entomobrya cf. nigriventris : Arbea and Jordana 1985: 61; Jordana et al. 1990: 57, 218.

Material examined.

Nine topotypic specimens from type locality in Hungary, Simontornya, com. Tolna, Barcsi Valley, hillside with loess steppe meadow, 120 m a.s.l., 46°45'59"N, 18°31'50"E, D-vac sample, 10 Aug. 2021 (leg. D. Winkler, N. Szigeti and G. Traser): three ♂♂ on slides (slide numbers as Nr. HNHM-collpr-915 to HNHM-collpr-916; and WD-coll-145); two ♀♀ on slide (slide numbers as Nr. HNHM-collpr-917; and WD-coll-146); three juveniles on slide (slide numbers as Nr. HNHM-collpr-918; WD-coll-147 to WD-coll-148), deposited at HNHM, and in the first author’s collection at SOE.

Redescription.

Habitus. Adult body length (excluding antennae) 1.20-2.49 mm (n = 7), holotype 1.20 mm (after Stach 1929). Body ground colour pale yellow (Fig. 7A-D ). Adult colour pattern (Fig. 7A-C ) characterised by a thin longitudinal stripe running along dorsal centreline, usually from Th II to Abd IV. Dark bluish black transverse stripes on anterior and posterior margins of Th II, and posterior margin of Th III to Abd III (broadest in Abd II). On each side of Abd IV, four irregular, broad, separate, or connected patches. Abd IV posteriorly with a dorsomedial rectangular patch. Abd V with two posterolateral patches. Head with broad dark band between antenna bases also connecting to eye patches and often continued longitudinally beyond them, in some cases reaching the lateral posterior part of the head. Dark violet pigment on antennae with increasing intensity from base to apex of segments. Juveniles (Fig. 7D ) with similar pattern but without irregular patches on Abd IV. Ventral body entirely dark in most adult specimens, in one specimen only the area between legs pigmented (in juveniles, ventral side with no dark pigmentation). In adults, dark pigmentation also on coxae and manubrium.

Head. 8+8 eyes, GH smaller than EF (Fig. 8A ). Interocular chaetotaxy with five chaetae (s, t, p, q, r). Antennae length 0.75-1.32 mm (n = 4). Antennal length to head diagonal length ratio 2.17-2.69 (n = 6). Relation of antennal joints I-IV as 1: 1.64-2:22: 1.57-2.11: 2.25-3.00 (n = 6). Ant IV with bi- or trilobed apical vesicle. Ant III sensillary organ composed of two sensory rods partially behind a cuticular fold, guarded by three short sensilla. Arrangement of chaetae on labrum 4/554, prelabral chaetae ciliated, posterior, median and anterior labral chaetae smooth. Labrum with four rounded labral papillae with spine-like projection (Fig. 8B ). Outer maxillary palp with two smooth chaetae and three smooth sublobal chaetae. Lateral process on labial papilla E not reaching apex of papilla. Labium chaetotaxy formed by five smooth “a” chaetae and, in basal row, by ciliated chaetae M1, R, E, L1, and L2 with R reduced (ratio of R/M1~0.5).

Body. Ratio of Abd IV/III length 4.00-5.89 (n = 6). No differentiated chaetae on tibiotarsus III, with exception of the smooth terminal chaeta opposite to tenent hair. Trochanteral organ with up to 19 spine-like chaetae (Fig. 8C ). Unguis and unguiculus of claw III as in Fig. 8D . Unguis inner side with sub-equal paired basal teeth at 50% from the inner edge, and with two more unpaired teeth at 72% and 87% from inner edge, respectively (holotype with three inner teeth on claw III, most distal unpaired one absent). Paired lateral teeth intermediate, at level slightly below the paired internal teeth. Unpaired dorsal tooth hardly observable, located approximately at 40% of distance from base. A small pretarsal chaeta present on both anterior and posterior surfaces. Unguiculus lanceolate, outer lamella smooth. Tibiotarsal tenent hair clavate, as long as claw. Ratio of smooth terminal chaeta / unguiculus around 1. Ventral tube with 19+19 ciliate chaetae of various size and 5+5 ciliated chaetae on posterior side (Fig. 8E ); lateral flap with nine ciliated and seven smooth chaetae. Manubrial plate with five or six chaetae (Fig. 8F ). Length of not ringed terminal dens ~ 2 × the length of mucro. Mucro with subapical tooth somewhat smaller than apical one; basal spine just reaching tip of subapical tooth.

Macrochaetotaxy (Fig. 8A, G-J ). Simplified Mac formula: 4(5)-1-0-3-1/3(4)-4(5)/2-5(7)/0-2-2/0-3(6)-10(0)4-3(4)-2(3).

Head (Fig. 8A ): H1 area with four or five Mac (An2, An3a1, An3a2, and An3 always present, one additional Mac from the An series present or absent); H2 area with one Mac (A5); H3 area without Mac; H4 area with three Mac (S1, S3, S4i); H5 area with one Mac (Ps2), Ps5 present as mes. Mesothorax (Fig. 8G ): area T1 with three or four Mac (m1, m2, m2i always present, m2i2 present or absent); T2 with four or five Mac (a5, m4, m4p always present, m4i present or absent). Abdomen: Abd II (Fig. 8H ) area A1 with two Mac (a2 and a3); area A2 with 5-7 Mac (m3, m3e, m3ep, m3ei, m3ea always present, m3eai present or absent; bilaterally an additional Mac present in one specimen); Abd III (Fig. 8I ) area A3 without Mac; area A4 with two Mac (a2 and a3), and area A5 with two Mac (m3 and m3e); Abd IV (Fig. 8J ) area A6 without Mac; area A7 with 3-6 Mac (A3, C1, E1 always present; Ae3, B2, B3 present or absent); area A8 with unpaired central Mac A04 present or absent, and with four Mac (A4a, Ae4, B4, C2a); area A9 with 3-4 Mac (A5, B5, and one Mac of uncertain homology always present, Ae5p present or absent); and area A10 with two or three Mac (A6 and B6 always present, Ae7 present or absent); sensillar formula from Th II to Abd V: 2,2/1,2,2,9,3; microsensillar formula from Th II. to Abd III: 1,0/1,0,1.

Ecology and distribution.

The type locality near the settlement Simontornya is situated on the loess ridges of the southern Transdanubian region of Hungary. According to historical maps, the area was pasture and mowed meadow centuries ago. Nowadays, the effects of intensive grazing can be observed on the grass vegetation, which consists of common species like Bothriochloa ischaemum , Galium verum , Salvia pratensis (Fig. 9 ). Based on the habitat and climatic characteristics, the species can be considered xerophilic. Notably, we also detected some of the co-existent species Ferenc Pillich collected together with E. nigriventris and sent to Jan Stach for determination. These include species Stach described together with E. nigriventris in the same paper ( Stach 1929): Orchesella hungarica Stach, 1929 and Pseudosira pillichi Stach, 1929, recently synonymised with Seira pallidipes Reuter, 1895 ( Winkler and Dányi 2017), as well as other Entomobrya species such as E. handschini Stach, 1922 and E. quinquelineata Börner, 1901.

Until now, E. nigriventris has been known only from its type locality in Hungary (Simontornya). Although the species has been frequently reported from open sand steppes in Central Hungary ( Hornung 1986; Loksa 1987; Traser 2002; Traser and Horváth-Szováti 2006; Flórián et al. 2019), these observations covered another species described in this article as E. arenaria sp. nov.. Traser et al. (2006) reported the species from West Hungary in a moss habitat, but re-examining their collected material proved this observation erroneous. In Spain, Arbea and Jordana (1985) detected a species ( E. cf. nigriventris ) that shows similarities based on the colour pattern. On the other hand, considering its habitat (beech forest, with moss cover in the more open parts), it is likely to represent another species.

Remarks.

Entomobrya nigriventris was described based on a single specimen ( Stach 1929), which entails the problem that the natural variability of the diagnostic characters cannot be determined. In addition to the new and essential information on the chaetotaxy and its variations, the examination of the newly collected specimens also allowed us to describe the size range and the colour pattern from the juvenile to the adult stage. Some of the already known characters (colour pattern, morphology of labral papillae, lateral process) are in accordance with the original description ( Stach 1929) and later redescriptions ( Stach 1963; Jordana 2012) based on the holotype. Morphology of Ant IV apical bulb can be bi- or trilobed (we found both variations in the newly collected specimens); in the holotype, it is trilobed ( Stach 1963). This moderate intraspecific variation has already been reported in other Entomobrya species ( Katz et al. 2015). However, there is a difference regarding the morphology of the claw III that must be mentioned. In the case of the holotype, the number of inner teeth on the claw is three, with only one (medial) unpaired tooth, while the apical unpaired tooth is reported to be absent ( Stach 1963; Jordana 2012). In the freshly collected specimens from the type locality, an additional minute apical tooth was always present. This variability, although not common, may occur in Entomobrya ( Jordana and Baquero 2006) and other derived genera of Entomobryomorpha , such as Lepidocyrtus (e.g., Mateos 2008; Winkler 2017), Pseudosinella ( Winkler and Mateos 2018), and Heteromurus ( Yoosefi Lafooraki and Shayanmehr 2014). It is also worth noting that Stach (1963) reported E. quinquelineata as a species with three inner teeth, while the original description ( Börner 1901) and its redescriptions ( Baquero and Jordana 2008; Jordana 2012) do not mention the absence of the apical unpaired tooth.

Apart from the dark ventral side and the presence of the longitudinal thin stripe running along the dorsal centreline, the colour pattern of E. nigriventris is very close to E. strigata Stach, 1963, originally described from Poland ( Stach 1963). It can be, however, distinguished by the morphology of labral papillae (with spine-like projection in E. nigriventris and with plain surface in E. strigata sensu Stach (1963)). The holotype of E. strigata is reported to be lost; therefore, to describe the dorsal macrochaetotaxy and additional characters missing from the original description, specimens collected in Armenia were used by Jordana (2012). This allowed us to observe further differences between the two species in the chaetotaxy. The head Mac formula differs slightly in E. strigata , with more Mac in the H2 and H5 areas. In contrast, there are fewer Mac in the area T1 of Th II and in the area A8 of Abd IV, and there are fewer chaetae also in the manubrial plate (Table 1 ).

Figures

Figure 7. Entomobrya nigriventris. Habitus A adult specimen, dorsal view B same adult specimen, ventral view C adult specimen, dorsolateral view D juvenile specimen, dorsal view. Scale bars: 0.5 mm.

Figure 8. Entomobrya nigriventris A head chaetotaxy B labral papillae C trochanteral organ D unguis and unguiculus of leg III E Ventral tube anterior view (left side) and posterior view (right side), circles-ciliated chaetae F Manubrial plate G Th II dorsal macrochaetotaxy H Abd II dorsal macrochaetotaxy I Abd III dorsal macrochaetotaxy J Abd IV dorsal macrochaetotaxy. Abbreviations: Abd = abdominal tergite; Th = thoracic tergite. Scale bars: 0.03 mm (A, D-F); 0.02 mm (B); 0.05 mm (C, G-J).

Figure 9. Entomobrya nigriventris. Type locality (Simontornya, Hungary).