Geophilus tenuis Popovici, Popa & Iorgu sp. nov.

Material examined.

Holotype. Romania • ♀ (MNINGA CHI 108), Ilfov County, Voluntari (44.5244°N, 26.1141°E), ca. 100 m asl., oak and hornbeam forest, upper soil layers, 16 April 2021, leg. G. Popovici.

Paratypes. Romania • 1 ♂ (MNINGA CHI 110), same as holotype, 23. 05. 2021; • 1 ♀ (MNINGA CHI 111), Ilfov County, Voluntari (44.5191°N, 26.1332°E), ca. 90 m asl., 28 March 2021, leg. G. Popovici; • 1 ♀ (MNINGA CHI 112), same as preceding, 04. 03. 2022; • 1 juvenile (MNINGA CHI 109), Ilfov County, Voluntari (44.5221°N, 26.0914°E), ca. 100 m asl., 30 May 2021, leg. G. Popovici.

Other materials.

Romania • 17 ♂♂ ♀♀, (GP), same as holotype.

Diagnosis.

Characterized by the following unique combination of characters: Small-sized Geophilus species (adult body length ≤ 13 mm); 43–47 leg-bearing segments; antennae 3.5–3.8 times longer than cephalic plate, articles II – VII elongate, 1.6–1.74 times longer than wide; cephalic plate 1.18 times longer than broad; clypeus with two evident clypeal areas; forcipular coxosternite approximately as long as wide, with incomplete chitin lines; inner margin of forcipular tarsungulum without crenulation; metasternites 2–12 with unconsolidated (sensu Crabill 1954), faint carpophagus structures and spindle-shaped pore fields; posterior metasternites including the penultimate with two posterior clusters of pores; coxopleuron of last leg-bearing segment with coxal pores opening individually, near the edge of the metasternite, partially covered by it; one isolated coxal pore opening laterally to the others; telopodite of ultimate leg pair with claw-shaped pretarsus.

Description of examined material.

Habitus. 43–47 leg-bearing segments in examined specimens. Body length 10–13 mm. Color of preserved specimens pale yellow with darker cephalic plate and forcipular segment.

Head and antennae (Fig. 5): Cephalic plate approximately 1.18 times longer than broad (0.58 mm long, 0.5 mm wide) with distinct dorsal reticulation, straight posterior margin and absent basal plate. No paramedian or other sulci. Chaetotaxy illustrated in Fig. 5 B. Antennae 3.5–3.8 times longer than head (1.8–2.2 mm long) and distinctly elongate with basal antennal articles 1.6–1.74 times longer than wide. Dorsal chaetotaxy as in Fig. 5 C. Articles I – IX with 2– 3 type a sensilla basally, articles X – XIII with 1 type a sensillum basally (Fig. 5 C). Article XIV with lateral groups of sensilla basiconica occupying approximately 30 % of its length and with a small cluster of type b sensilla at its distal apex (Fig. 5 D).

Clypeus (Fig. 6 A, B): Clypeus uniformly reticulated, with two evident clypeal areas. With three pairs of setae, the postantennal and posterior being smaller than the intermediate pair. (Fig. 6 A). Clypeal areas lighter than surrounding cuticle, with indistinct but visible reticulation.

Labrum (Fig. 6 A, B): Labrum with distinct lateral parts. Intermediate part with 5–6 tubercles, but only 2–3 visibly well-sclerotized in the center. Lateral parts with 5–7 hyaline filaments.

Mandible (Fig. 6 E): One single pectinate lamella present on distal edge. Of a typical aspect for the genus.

First maxillae (Fig. 6 C, D). Coxosternite entire. Distinct, sub-triangular coxal projections with 3–4 sensilla trichodea and 1–3 sensilla microtrichodea on their ventral side. Coxosternal and telopodal lappets present, weakly developed (Fig. 6 D). Articulation of telopodite indistinct.

Second maxillae (Fig. 6 C, D). Coxosternite undivided, distinctly reticulated and with broadly concave anterior margin. Row of sensilla trichodea present medio-ventrally. Telopodite articles elongate (article I ca. 1.2, article II ca. 1.0, and article III ca. 1.7 times longer than wide) with distinct condyles and articulations. All articles with 1–3 sensilla coeloconica laterally. Pretarsus simple, claw-shaped with small pore opening distally (Fig. 6 D).

Forcipular segment (Fig. 7): Forcipular tergite anteriorly narrowing, trapeziform. Forcipular coxosternite approximately as wide as long. Chitin lines vanishing before reaching the condyles, pointing laterally to them. Anterior margin with a shallow but evident notch and without denticles. Isolated reticulation pattern and chaetotaxy as in Fig. 7 D. Forcipules extending slightly past the anterior margin of the cephalic plate when closed. Forcipular trochanteroprefemur ca. 1.3 times longer than wide. Denticle at the base of tarsungulum conspicuous, straight, with rounded apex. Tarsungulum with smooth inner margin. All forcipular articles present a prominent sensillum coeloconicum on the internal side but no denticles (Fig. 7 A, B). Calyx of venom gland oval, opening in femoroid (Fig. 7 C).

Trunk (Fig. 8). Tergites wider than long, without grooves or sulci, indistinctly reticulated and moderately setose. Walking legs largely homonomous along the entire trunk (Fig. 8 B). Pretarus claw-shaped, basally armed with a small accessory spine. Presternites well-developed, divided along the entire trunk. Metasternites sub-trapezoidal. First metasternite with central cluster of pores (Fig. 8 A). Pore fields present on all sternites excepting that of the ultimate leg-bearing segment. Anterior segments (2–15) with spindle-shaped, undivided pore fields. Carpophagus structures faint, present on sternites 2–12. Posterior metasternites elongate, 1.4–1.5 times longer than broad, and with two small, approximately circular pore fields located in the posterior third. All sternites with two converging rows of sensilla trichodea anteriorly and two pairs of large sensilla trichodea laterally.

Last leg-bearing segment (Figs 9 A, 9 B, 10): Ultimate pleuropretergite complete. Ultimate metatergite 1.2 times wider than long. Ultimate metasternite trapezoidal, ca. 1.5 times wider than long, with straight posterior margin. Coxopleurae moderately enlarged, with 2–3 coxal organs opening close to the edge of the metasternite, partly covered by it, and one isolated posterior pore, reduced in size. Telopodite elongate in female holotype (4.1 times longer than metasternite), more densely setose on the ventral side and ending in a strong, curved pretarsus provided with a small accessory spine. Telopodite moderately swollen in male paratype (4.2 times longer than metasternite), more densely setose on ventral side.

Postpedal segments (Figs 9 B, 10): Female with weakly bilobed gonopodal lamina (Fig. 9 B). Male with penis flanked by two biarticulate, densely setose gonopods (Fig. 10). Anal pores distinct, opening near the margin of the anal valves (covered by gonopods in male).

Juvenile. Clypeus with conspicuous, uniform reticulation (cells less numerous and larger relative to size of clypeus than in adults), resolving to smaller cells near the medial pair of setae (Fig. 6 B). Forcipular trochanteroprefemur approximately as long as wide (Fig. 7 E). Anterior metasternites with band of pores posteriorly. Posterior metasternites with pore fields indistinct (Fig. 8 C). Last leg-bearing segment coxopleuron with only the one isolated coxal pore present (Fig. 9 C). Gonopodal lamina indistinct.

Etymology.

Derived from the Latin term for “ meager ” or “ feeble ” (“ tenuis ”), in recognition of its morphological similarity to the initially recognized G. captiosus sp. nov. as well as its smaller body size and gracile habitus.

Remarks.

G. tenuis sp. nov. greatly resembles G. captiosus sp. nov. in overall morphology, with many differences between the two species known to be characters that vary with respect to body size in Geophilidae (Horneland and Meidell 2009; Gregory and Barber 2010; Peretti and Bonato 2016; Stojanović et al. 2020). A consistent morphological difference between the two not subject to allometric scaling is the arrangement of coxal pores, which open at the edges of the ultimate leg-bearing segment metasternite in G. tenuis sp. nov. and are scattered over the entire ventrolateral surface of the coxopleuron in G. captiosus sp. nov. (Figs 4, 9, 10, Table 1). G. pusillifrater overlaps in many morphological characters with G. tenuis sp. nov., both being small, oligopodous species (Stojanović et al. 2019). G. pusillifrater can be distinguished from G. tenuis sp. nov. by the absence of clypeal areas, first maxillary lappets, and carpophagus structures; the earlier mid-body transition in metasternal pore-field shape; the absence of pore fields on the posterior sternites; the lower number of coxal organs; and the sexually dimorphic condition of the male ultimate leg-pair pretarsus, which is reduced to a small tubercle (Lewis 1961; Eason 1964). G. pygmaeus similarly resembles G. tenuis sp. nov. in size, number of leg-bearing segments, and most other morphological characters (Peretti and Bonato 2016) but clearly differs from it in the elongation of the proximal antennal articles (not elongate), the absence of clypeal areas, the lower number of tubercles on the mid-piece of the labrum (two), and the arrangement of the coxal organs (one opening at the anterior tip of the coxopleuron, covered by presternites; an isolated coxal organ opening centrally on the coxopleuron, parallel with the posterior end of the line of coxal organs opening near the edge of the metasternite) (Table 1). Small specimens or juveniles of G. flavus may superficially overlap with G. tenuis sp. nov. in meristic or continuous characters that scale allometrically with body size but can be readily distinguished from the new species by the serrate inner edge of the tarsungulum (lacking serrations in G. tenuis sp. nov.), the lack of a conspicuous isolated coxal pore (present in G. tenuis sp. nov.), and the reduction of the last leg pretarsus (not reduced in size in G. tenuis sp. nov.). The species G. osquidatum, G. seurati, and G. zagreus are not known to overlap in adult body length or number of leg-bearing segments with G. tenuis sp. nov., but they are additionally distinguished from the new species in having serrations on the inner edge of the tarsungulum (G. osquidatum, G. seurati), coxal pores that open across the entire ventral surface of the coxopleuron (G. zagreus), no isolated coxal pore (G. osquidatum, G. seurati), and a reduced last leg pretarsus (G. osquidatum, G. seurati). G. tenuis sp. nov. can be distinguished from G. proximus by the morphology of the carpophagus structures (strongly sclerotized and consolidated sensu Crabill (1954) in G. proximus; unconsolidated sensu Crabill 1954 in G. tenuis sp. nov.), the elongation of its forcipules (tarsungula not protruding beyond the anterior margin of the head in G. proximus; protruding in G. tenuis sp. nov.), the absence of pore fields on the posterior trunk metasternites (present in G. tenuis sp. nov.), and the arrangement of the coxal organs.