Litocampa Silvestri, 1933

Sánchez-García, Alba, Sendra, Alberto, Davis, Steven R. & Grimaldi, David A., 2024, ‘ Dawn’ hexapods in Cenozoic ambers (Diplura: Campodeoidea), Zoological Journal of the Linnean Society 201 (1), pp. 136-158 : 144-149

Genus Litocampa Silvestri, 1933

Type species: Litocampa neotropica Silvestri, 1933 .

Litocampa eobaltica Sánchez-García, Sendra and Grimaldi sp. nov.

( Figs 7–10 )

LSID: urn:lsid:zoobank.org:act:687BF785-5BE6-488A-B531-147DF9F51906

Etymology: The specific epithet is in reference to the geological epoch (Eocene) and amber of origin (Baltic amber).

Material: Holotype AMNH Ba-JVe66 ( Figs 7–9 ), sex unknown, adult; held in the AMNH; specimen virtually complete, with the left antenna broken; a reddish halo is around most of the specimen; observable ventrally (with high distortion) and dorsally; the piece is very transparent, orange in colour, embedded in a block of EpoTek resin trimmed to 1.9 cm × 1.4 cm × 0.7 cm; syninclusions include an ant and plant trichomes.

Paratype AMNH Ba-JVe277 ( Fig. 10 ), sex unknown, adult; held in the AMNH; specimen virtually complete, with the left cercus broken; observable ventrally (with high distortion) and dorsally; the fossilized position of the specimen precludes several measurements and hinders examination of legs and ventral structures; the piece is very transparent, orange in colour, embedded in a block of EpoTek resin trimmed to 2.7 cm × 1.6 cm × 1 cm; in spider webbing, syninclusions include one acari.

Occurrence: Eocene, Baltic amber.

Diagnosis: Cuticle with microdenticles. Frontal process not protruding. Antenna three-fifths length of body, with 25 antennomeres, moniliform. Distribution of thoracic macrosetae: 1 + 1 ma, 1 + 1 la, 1 + 1 lp on pronotum and mesonotum, and 1 + 1 ma, 1 + 1 lp on metanotum; lp and marginal setae robust. Metathoracic leg reaching abdominal segment VI; femur without dorsal macrosetae and with one ventral macroseta; tibia with one ventral macroseta; claws subequal, elbowed, with small and smooth lateral crests; pretarsal lateral processes setiform and smooth. Distribution of abdominal macrosetae: 1 + 1 la, 1 + 1 lp on VI–VII, and 3 + 3 lp on VIII. Cerci slightly longer than body, with five primary articles, with whorls of setae and macrosetae smooth.

Description (based on holotype): Sex unknown, adult.

Body: Length 2.35 mm. Cuticle with microdenticles perceptible under compound microscope ( Fig. 10C ); body highly setose, with long, thin, smooth clothing setae.

Head: Length 0.39mm,0.16 × length of body.Frontal process not protruding. Labial palp not visible. Antenna (non-regenerated) length 1.42 mm, 0.6 × length of body, with 25 antennomeres; antennomeres I and II subrectangular; antennomere III onwards moniliform, as long as wide (length and width 0.07 mm); apical antennomere length 0.09 mm, width 0.07 mm, with a cupuliform organ occupying 1/17th of its length, with sensilla not visible; trichobotria visible in antennomeres III–V ( Fig. 8B ); medial and distal antennomeres with whorls of short, thin and smooth setae.

Thorax: Length 0.66 mm, 0.28 × length of body. Distribution of macrosetae: pronotum with 1 + 1 ma, 1 + 1 la, 1 + 1 lp; mesonotum with 1 + 1 ma, 1 + 1 la, 1 + 1 lp; and metanotum with 1 + 1 ma, 1 + 1 lp ( Figs 8A , 9E, F , 10B ); ma and la macrosetae short and thin; lp macrosetae longer and robust; all macrosetae with very short barbs on one side, giving a serrate appearance; marginal setae longer than clothing setae and robust, with barbs as for macrosetae. Legs slightly elongated, with metathoracic leg reaching abdominal segment VI; length of metathoracic leg segments: femur 0.17 mm, tibia 0.16 mm, tarsus including pretarsus 0.15 mm; femur with one long, thin, smooth ventral macroseta; tibia with one long, thin, smooth ventral macroseta and two regular calcars distally ( Figs 8E, F , 9A–D ); femur and tibia without dorsal macrosetae; tarsus with typical setae along ventral side; pretarsus with subequal elbowlike claws with small and smooth lateral crests; pretarsal lateral processes setiform and smooth.

Abdomen: Length 1.30 mm, 0.55 × length of body. Distribution of macrosetae on tergites: VI–VII with 1 + 1 la, 1 + 1 lp; VIII with 3 + 3 lp; IX at least with 3 + 3 lp; macrosetae long and thick, with very short barbs on one side along distal half or third, giving a serrate appearance. Urosternite details mostly obscured (stylus II and eversible vesicles not visible). Pairs of styli visible from sternites III to VII; stylus ( Fig. 8D ) with smooth apical, subapical and ventromedial setae; subapical and ventromedial setae apparently longer than apical setae. Both cerci complete (non-regenerated), length 2.54 mm, 1.08 × length of body; divided into a basal article plus five primary articles; basal article length 0.41 mm, subdivided into five secondary articles; primary articles increasing in length towards the apex, with four to five constrictions (first primary article 0.27 mm; second 0.32 mm; third 0.45 mm; fourth 0.52 mm; fifth 0.57 mm); cercal articles with four to six whorls of smooth macrosetae accompanied by whorls of long, thin, smooth setae; the number of whorls increasing from first to fifth primary articles; each constriction between articles preceded by a whorl of short, thin, smooth setae.

Descriptive notes on paratype AMNH Ba-JVe277: Sex unknown, adult. General description is as for the holotype, with the following measurements: body length 1.91 mm; head length 0.29 mm, 0.15 × length of body, showing the occipital Y-suture; antenna length 1.09 mm, 0.57 × length of body, with the distal-most antennomere more robust than in the holotype ( Fig. 10D ); thorax length 0.7 mm, 0.37 × length of body; abdomen length 0.92 mm, 0.48 × length of body; and cerci length 3.91 mm, 2.05 × length of body.

Remarks: The new Litocampa species fits within the subfamily Campodeinae owing to the presence of a maximum of 3 + 3 macrosetae on the pronotum ( Condé 1956, Paclt 1957). The presence of claws with lateral crests, in combination with the presence of lp macrosetae on the pro-, meso- and metanotum is characteristic of the genus Litocampa ( Sendra et al. 2016) . The genus Litocampa comprises ~30 species, mostly distributed in the Holartic region in soil and cave habitats. The absence of dorsal macrosetae on femora III and the macrosetae formula 1 + 1 la, 1 + 1 lp, without ma, on abdominal tergites VI–VII excludes most of the Litocampa species. In this sense, Li. eobaltica resembles a few species, such as the extant species Litocampa enriqueriojai Sendra and García, 2016 , but differs in the microdenticles of the cuticle, the number of antennomeres, the robust lp compared with ma and la macrosetae, and the robust marginal setae. The abundance of clothing setae indicates that both specimens are adults.

Figures

Figure 7. Dorsal photomicrograph of holotype of Litocampa eobaltica, AMNH Ba-JVe66, in Eocene Baltic amber.

Figure 8. Camera lucida drawings of holotype of Litocampa eobaltica, AMNH Ba-JVe66, in Eocene Baltic amber. A, detail of thorax, showing the distribution of macrosetae.B, detail of basal antennomeres.C, dorsal habitus.D, detail of stylus.E, detail of pretarsus and tibia of leg II; asterisk indicates the ventral macroseta on the tibia. F, detail of pretarsus and tibia of leg III; asterisk indicates the ventral macroseta on the tibia. Abbreviation:c, calcar.

Figure 9. Photomicrographs of holotype of Litocampa eobaltica, AMNH Ba-JVe66, in Eocene Baltic amber. A, detail of left leg II; asterisk indicates the ventral macroseta on the tibia. B, detail of pretarsus in A. C, detail of left leg III; asterisk indicates the ventral macroseta on the tibia. D, detail of pretarsus in C. E, distribution of macrosetae on pronotum and mesonotum. F, distribution of macrosetae on metanotum. Abbreviation: c, calcar.

Figure 10. Photomicrograph of paratype of Litocampa eobaltica, AMNH Ba-JVe277, in Eocene Baltic amber. A, dorsal habitus; arrows point to the spider web.B, thorax in dorsal view, showing the distribution of macrosetae; the box labelled C corresponds to panel C. C, detail of microdenticles of the cuticle.D, head and thorax in ventral view.