Machilinus obscurus Kaplin, 2020

Kaplin, Vladimir & Martynov, Vladimir, 2020, Three new species of bristletails of the families Meinertellidae and Machilidae (Archaeognatha) from Ukraine and Southern Russia, Acta Entomologica Musei Nationalis Pragae 60 (2), pp. 463-474 : 467-469

Machilinus obscurus Kaplin , sp. nov.

( Figs 4 , 5 )

Type material. HƟΓƟΤΥΡΕ: 3 (slide-mounted, ZIN), UKRAINE: Donetsk region, near Starobeshevo, 47°45′01″N, 38°01′45″E, 140 m a.s.l., rock outcrops, stony steppe, under stones, July 22, 2019, V. Martynov leg. PΑ*©ΑΤΥΡΕඌ: 5 ♀♀ (one on slides), 2 33, the same locality, V. Martynov leg. ( ZIN).

Description. Body length: male 6.8–6.9 mm, female 7.2–7.8 mm. Body width: male 2.0– 2.2 mm, female 2.2–2.3 mm. Antennal length: 4.5 mm in male, 3.7–4.3 mm in female (broken); cercal length 2.2–2.3 mm in male, 2.7–3.0 mm in female; total eyes width: 0.76–0.84 mm in male, 0.81–0.87 mm in female; eye length: 0.48–0.53 mm in male, 0.50–0.53 mm in female; paired ocelli width: 0.17–0.21 mm in both sexes; paired ocelli length: 0.11–0.13 mm in both sexes. Ovipositor length 3.0– 3.3 mm. Thoracic coxal styli absent. Head including antennae, maxillary and labial palpi, clypeus, labrum, labium, and legs without scales.

General body color light yellow or whitish, with purple -brown hypodermal pigment of medium intensity. Color of body scales mostly brown and dark brown. Antennae in both sexes shorter than body. Ratio of length to width of scapus about 2.0 in male and 2.2 in female ( Fig. 4A ). Dorsal surface of scapus and pedicellus with slightly pigmented simple chaetae. Several of these chaetae on basal part of scapus smaller and colorless. Distal chains of flagellum divided into eight annuli in both sexes. Two or three distal chains of antennal flagellum broken. Frons and clypeus of male with relatively numerous short simple chaetae ( Fig. 4B ). Cercus approximately 0.32–0.33 times as long as body length in male and 0.35–0.40 times in female. Cerci with 18–20 articles in male and 22–24 in female. Articles of cerci, except for apical one or two, with 1–3 supporting spines on inner side. Cerci and caudal filament also with long chaetae.

Compound eyes unicolorous, dark or almost black (in ethanol). Ratio of length to width of compound eye about 1.2–1.3 in both sexes; ratio of contact line length to eye length 0.66–0.70 in both sexes. Paired ocelli oval, sublateral, white; 1.7 times as wide as long in male and 1.5–1.6 times in female ( Fig. 4B ). Distance between inner margins of ocelli 0.56–0.58 and between their outer margins 0.96– 0.98 times total width of compound eye, in both sexes.

Apical article of maxillary palpus of male 0.54–0.56 and female 0.58–0.60 times as long as preceding one. Dorsal surface of 7 th, 6 th and 5 th articles of maxillary palpus with 8 or 9, 10 or 11, and 3 hyaline spines in male, and 9, 11 and 2 spines in female, respectively. 5 th article of maxillary palpus 1.48–1.50 times as long as 4 th article in male and 1.43–1.47 times in female ( Figs 4C, D ). Second article of male maxillary palpus noticeably curved with external lateral apical apophysis, which is absent in female maxillary palpus. Apophysis surpassing distal end of 2 nd article. Outer side of apophysis with about 15 dark lateral chaetae and several longer simple chaetae in upper part of apophysis, without ventral spiniform chaetae. 3 rd article of male maxillary palpus with numerous dark brown relatively long thick chaetae, without ventral spines.Apical article of labial palpus triangularly oval, 2.9 times as long as wide in male and 3.7 times in female ( Figs 4E, F ). Mandibles in both sexes with two teeth ( Fig. 4G ).

Fore femur and tibia widened in both sexes. Ratios of lengths to widths of coxa, femur, tibia, and tarsus as shown in Table 5. Ratio of length of 3 rd tarsomere to total length of tarsus 0.40–0.41 in male and 0.37–0.38 in female ( Fig. 4H ). Legs of male without long thin chaetae. Ventral surface of femora, tibiae and tarsi with spine-like chaetae as shown in Table 6. Pretarsi with well-developed conical strongly pigmented support protrusion as in M. petrophilus sp. nov. ( Fig. 1K ).

In both sexes, abdominal segments II–VII with 1 + 1 eversible vesicles. Posterior angle of urosternites more than 130° ( Table 7). Ratio of lengths of urosternite and urocoxite I in male about 0.29. Ratios of lengths of urosternite, urocoxite and stylus (without apical spine) on urites II–IX as shown in Table 7. Inner posterior lobes of urocoxites VII of female protruding; ratio of length to their total width about 0.45.

Inner margins of its lateral expansions with about 20–22 + 20–22 macrochaetae in both sexes. Lateral margins of mesonotum with 60–65 + 60–65, metanotum with 20–22 + 20–22 macrochaetae in both sexes. Lateral parts of pronotum with 20–22 thin chaetae in male and 15–18 in female, those of mesonotum with 95–105 in both sexes, those of metanotum with 55–60 + 55–60 in male and 4–5 + 4–5 in female. Anterior part of urotergite I with 10–12 + 10–12 sublateral chaetae as in M. petrophilus ( Fig. 2E ), urotergites II–VIII and X without chaetae, urotergite IX with 1 + 1 mesochaetae in both sexes. Anterior part of urocoxites I with about 18 + 18 chaetae in both sexes. Distribution of sublateral chaetae on urocoxites II–IX as shown in Table 8.

Ovipositor slender, elongate, extending much further than apex of styli IX ( Fig. 5A ). Anterior and posterior gonapophyses with 77 and 79 articles, respectively. One basal division of anterior gonapophyses and about 52 proximal divisions of posterior gonapophyses glabrous.

Distal divisions of anterior and posterior gonapophyses with 5, and 9 or 10 chaetae, respectively (not counting sensory setae and apical spines) ( Figs 5B, C ). About 37 distal divisions of anterior gonapophyses and 28 distal divisions of posterior gonapophyses with long setae.

Apical spines of gonapophyses as long as about 3.3 distal divisions combined.

Male genitalia without parameres. Penis does not significantly attain the apex of urocoxites IX, ratio of distance between apexes of penis and urocoxites IX to width of apical article of penis about 2.4 ( Fig. 5D ). Ratio of lengths of apical and basal articles of penis about 1.0.

Differential diagnosis. Machilinus obscurus sp. nov. belongs to the group “ rupestris ” with 10 described species that do not possess spines on the 3 rd and 2 nd articles of the maxillary palpus in the male (MΕΝĐΕඌ 1977, NƟΤΑ*©ΙƟ-MUΝƟƶ et al 2000). Among them, M. rupestris Silvestri, 1904 has 3 subspecies. The main morphological differences between M. obscurus sp. nov. and its closest congeners are shown in Table 9. Only the compound eyes of M. obscurus sp. nov. are uniformly dark and almost black. Forehead and clypeus of Machilinus obscurus sp. nov. and M. spinosus bear numerous short chaetae but these species are easily distinguished by the color of the compound eyes, the ratio of length to width of the eye, eye contact line length and other features. 5 th article of the male maxillary palpus of M. botellai and M. casasecai bears numerous long thin chaetae which are absent in the new species and other species of this group (BΑർ*ü 1974, GΑ*°U et al. 1992). M. obscurus sp. nov. is similar to M. rosaliae in number of spines on legs, ratio of length of apical article of labial palpus to its width in the male compared to the female, numerous small chaetae on clypeus, ratio of lengths of apical and preapical articles of maxillary palpus and ratio of length to width of compound eye. Machilinus rosaliae differs from the new species in the color of compound eyes, ratio of lengths of contact line and eyes, in the absence of numerous small chaetae on frons ( Table 9). The apical article of the male labial palpus of M. rosaliae displays sexual dimorphism. The apophysis does not surpass the distal end of the 2 nd article (MΕΝĐΕඌ 1977).

Etymology. The species name obscurus is a Latin adjective meaning dark, referring to the predominant color of the body scales.

Habitats. Outputs of Upper Carboniferous limestones in the Kalmius River valley. Petrophytic steppe communities with dominance of Stipa lessingiana Trin. & Rupr. , S. grafiana Steven , Thymus dimorphus Klokov & Des. -Shost., T. calcareus Klokov & Des. -Shost., Ephedra distachya L., Koeleria bre vis Steven., Ulmus glabra Huds. , Prunua stepposa Kotov. , Spiraea hypericifolia L., Caragana scythica (Kom.) Pojark. , Convolvulus lineatus L., and Rosa subpygmaea Chrshan. ( Fig. 9 ).

Figures

Fig. 4. Machilinus obscurus sp. nov. (A–C, F, G, H – male, holotype; D, E – female, paratype):A – scapus, pedicellus and two basal annuli of flagellum; B – head, front view; C, D – maxillary palpus; E, F – labial palpus and labium (part); G – distal part of mandible; H – hind leg. Scale bar: 0.1 mm.

Fig. 5. Machilinus obscurus sp. nov. (D – male, holotype; A–C – female, paratype): A – urocoxite IX, with anterior gonapophysis; B – distal part of anterior gonapophyses; C – distal part of posterior gonapophysis; D – urocoxite IX, with penis. Scale bar: 0.1 mm.

Fig. 1. Machilinus petrophilus sp. nov. (B, D, E, G–K – male, holotype; A, C, F – female, paratype): A – scapus and pedicellus of antenna; B – head, frontal view; C – distal part of cercus; D – maxillary palpus; E – 1st–3rd articles of maxillary palpus; F, G – labial palpus and labium (part); H – apical article of labial palpus; I – distal part of mandible; J – part of hind leg; K – pretarsus of hind leg. Scale bar: 0.1 mm.

Fig. 2. Machilinus petrophilus sp. nov. (A, D – male, holotype; B, C, E – female, paratype): A, B – urosternite and urocoxites V (part); C – urosternite and urocoxites VII (part); D – pronotum (part); E – urotergite I (part). Scale bar: 0.1 mm.

Figs 8–9. Habitats of the new species. 8 – habitat of Machilinus petrophilus sp. nov., Amvrosiivka, July 22, 2019. 9 – habitat of Machilinus obscurus sp. nov., Starobeshevo, right bank of the Kalmius river, September 24, 2019. (Photos by V. Martynov).