Description

Description based on Japanese specimens. Body length 923 μm in extended condition. Head length 103 – 109 μm; width 70 – 76 μm; labrum short, 5 – 6 μm, LR = 17 – 20. Cephalic setae l 3, l 5, sd 4 short setiform, 6 – 7 μm; sd 5 and d 6 absent; d 7 and sd 7 subequal length, 15 – 17 μm (Fig. 11 A). Maxillary palpus with two sensilla on penultimate seg- ment, dorsal sensillum, 9 μm, slightly longer than ventral one, 7 μm (Fig. 11 B). Labial palpus with three setae and one sensillum (Fig. 11 C). Canal of maxillary gland simple (Fig. 11 D), CF = 9 – 11. Pseudoculus circular or slightly broader than long (Fig. 11 E), 7 – 9 μm x 9 μm, PR = 13 – 14. Pore fp present (Fig. 11 A). Foretarsus (Figs. 11 F, G) 72 – 77 μm; claw 24 – 26 μm, TR = 2.9 – 3.1; empodium 3 – 4 μm, EU = 0.1 – 0.2. Dorsal sensillum t 1 claviform, almost same level with α 3, BS = 0.4 – 0.5; t 2 thin, situated at same level with d; t 3 small knob-like. Exterior sensillum a situated between γ 1 and α 3, its apex reaching base of f; b almost same length as c; c almost same level with α 3; d situated at same level with t 2; apices of a, b, c and d each reaching base of f; e situated posterior to α 5; f at about halfway between e and g; g slightly distal to t 3; apices of e, f and g surpassing tarsus. Interior sensillum a' broad, slightly posterior to t 1, its apex surpassing base of b'; b' slightly distal to t 2, its apex not reaching base of c'; c' at same level with α 6, its apex surpassing tarsus. Single pore present near bases of c and t 3, respectively. Setae β 2 sensillum-like; δ 1 – 5 short. Middle tarsus 33 – 35 μm, its claw 14 – 17 μm; hind tarsus 39 – 41 μm, its claw 17 – 18 μm. Body chaetotaxy as in Table 3 and Figs. 12 A – G. On thoracic tergites II – III (Fig. 12 A), P 1 a and P 2 a short setiform; P 1 a halfway between P 1 and P 2; P 2 a slightly nearer to P 3 than to P 2; P 5 a rudimentary. 1 and 2 on thoracic tergite I 27 – 30 and 11 – 13 μm; P 1, P 1 a and P 2 on thoracic tergite II 20 – 25, 5 – 7 and 32 – 33 μm. Abdominal tergites II – VII with four pairs of anterior setae (A 1, A 2, A 4, A 5); but A 1 on VII often asymmetrical absent (Fig. 11 B); P 3 on II – VI situated anterior to other posterior setae (Fig. 11 B); P 1 a on I – VI absent; P 2 a and P 4 a on I – VII and P 1 a on VII short setae, about 1 / 4 of P 1 in length; P 2 a on II – VI nearer to P 2 than to P 3; on VII P 1 a nearer to P 1 than to P 2, P 2 a at middle between P 2 and P 3. Sternite VIII with a single row of four setae; P 1 a on sternites II – VI similar to dorsal ones; P 1 a on VII slightly longer than those on sternites II – VI. P 1, P 2 and accessory setae (P 2 a, P 4 a) on abdominal tergite VI 25 – 26, 30 and 6 – 7 μm; P 1, P 1 a and P 2 on VII 26 – 28, 6 – 7 and 28 μm; P 1 a on sternite VI 6 – 7 μm; one on VII 7 – 8 μm. Thoracic tergite II – III with pore sl (Fig. 11 A). Pore psm present on abdominal tergites I – VIII, those on VIII with accompanying teeth (Fig. 11 C); al on V-VII (Fig. 11 B); lt on VII (Fig. 11 G). Sternite V with spsm; VI with two pairs of spsm; VII with spsm and spm (Fig. 11 G). Abdominal appendage II – III with two setae (Fig. 11 H), apical seta, 5 μm, about 1 / 3 length of subapical one, 14 – 16 μm. On abdomen VIII, striate band developed, striae distinct (Fig. 12 C); comb with about 9 teeth; scattered teeth present on anterior part (Fig. 12 C). Anterior line on abdominal sternites II – III continuous (Fig. 12 D). Female squama genitalis with stout pointed acrostylus (Fig. 11 I). Maturus junior: Body length 656 μm in extended condition. Head length 87 – 92 μm, width 61 – 65 μm, LR = 19 – 28; pseudoculus slightly longer than width or circular, 7 μm x 7 – 8 μm, PR = 12 – 14; CF = 10 – 11; pore fp often invisible. Foretarsus 62 – 65 μm; claw 21 – 23 μm, TR = 2.9 – 3.0; empodium 3 – 4 μm, EU = 0.1 – 0.2. Shape and posi- tion of foretarsal sensilla, and pores same as those of imago, BS = 0.4. Middle tarsus 25 – 28 μm, its claw 15 – 16 μm; hind tarsus 28 – 31 μm, its claw 15 – 18 μm. Body porotaxy almost same as those of imago, but sl on thoracic tergites II – III often invisible; lt on abdomen VII missing. Scattered small teeth present on anterior part on abdomen VIII. Larva II: Body length 611 μm in extended condition. Head length 77 – 86 μm, width 58 – 61 μm, LR = 26 – 32; pseudoculus slightly longer than width or circular, 6 – 7 μm x 7 – 8 μm, PR = 12 – 14; CF = 10 – 12; pore fp missing. Foretarsus 51 – 56 μm; claw 18 – 20 μm, TR = 2.7 – 3.0; empodium 3 – 4 μm, EU = 0.1 – 0.2. Foretarsal sensilla b’ missing, BS = 0.4 – 0.5; pores same as those of preceding stages. Middle tarsus 24 – 28 μm, its claw 13 – 15 μm; hind tarsus 26 – 30 μm, its claw 14 – 15 μm. Pore al present on abdominal tergites I – VII; psm on V – VIII, those on V asymmetric or invisible, those on VIII with accompanying teeth; spsm present on abdominal sternites V – VII, those on V often missing, those on VII often asymmetric. Larva I: Body length 299 μm in compact condition. Head length 76 μm, width 49 μm; rostrum indistinct; pseudoculus slightly longer than width, 7 μm x 5 μm, PR = 12; CF = 12; pore fp absent. Foretarsus 42 μm; claw 18 μm, TR = 2.2; empodium 3 μm, EU = 0.2; BS = 0.4; sensilla b’ and c’ missing; pores absent. Pore psm present on abdominal tergites VII – VIII, those on VIII without accompanying teeth, a pair of ventral pore present at side on telson. Chaetotaxic variation. The chaetotaxy is quite variable and more than one irregularity exists in many specimens. The following anomalies were recorded. Imagines (176 specimens): thoracic tergite I — asymmetric presence of additional P 1 (2 examples), asymmetric absence of P 2 a (1 ex.); thoracic sternite I, presence of additional Ac (2 exs.); thoracic sternite II — presence of additional ventral A 2 (1 ex.); abdominal tergite I — symmetric presence of additional A 2 (1 ex.); abdominal tergite II — absence of A 1 (1 ex.), asymmetric absence of A 2 (1 ex.), asymmetric presence of A 3 (2 ex.), asymmetric absence of A 4 (1 ex.), asymmetric presence of additional A 5 (1 ex.), absence of P 1 (1 ex.), absence of P 2 (1 ex.), asymmetric absence of P 2 a (1 ex.); abdominal tergite III — asymmetric absence of A 4 (5 exs.); abdominal tergite IV — asymmetric absence of A 1 (1 ex.); abdominal tergite V — asymmetric presence of additional A 1 (1 ex.), asymmetric presence of A 3 (1 ex.), asymmetric absence of A 4 (5 exs.), asymmetric absence of P 2 (1 ex.); abdominal tergite VI — asymmetric absence of A 2 (1 ex.), asymmetric presence of A 3 (1 ex.), asymmetric absence of A 4 (4 exs.), asymmetric absence of P 1 and P 2 (1 ex.); abdominal tergite VII — asymmetric absence of A 1 (158 exs.), asymmetric absence of A 2 (2 exs.), asymmetric presence of A 3 (5 exs.); abdominal tergite VIII — absence of M 1 (1 ex.), presence of Mc instead of M 1 (4 exs.), presence of Mc (1 ex.), asymmetric absence of M 2 (1 ex.); abdominal tergite IX — asymmetric absence of 1 (1 ex.), asymmetric presence of additional 1 (1 ex.); abdominal segment X — asymmetric presence of additional 1 (1 ex.); abdominal sternite III — presence of one seta lateroposterior to Ac (2 exs.); abdominal sternite IV — asymmetric presence of A 1 (6 exs.), presence of one seta lateroposterior to Ac (1 ex.), asymmetric presence of P 1 (1 ex.); abdominal sternite V — asymmetric presence of A 1 (3 exs.), presence of A 1 instead of Ac (1 ex.); abdominal sternite VI — asymmetric absence of P 3 (1 ex.); abdominal sternite VII — presence of one seta between A 2 and P 2 (1 ex.), asymmetric absence of P 1 a (1 ex.); abdominal sternite VIII — presence of 5 setae (30 exs.) and 6 setae (1 ex.); abdominal sternite X — asymmetric absence of seta 1 (1 ex.). Maturi juniores (39 specimens): abdominal tergite II — asymmetric presence of A 4 (1 ex.); abdominal tergite III — asymmetric absence of A 1 (2 exs.), asymmetric absence of A 2 (1 ex.): abdominal tergite V — asymmetric absence of A 1 (1 ex.), asymmetric presence of A 4 (1 ex.); abdominal tergite VII — asymmetric (37 exs.) and symmetric (2 exs.) absence of A 1, asymmetric (18 exs.) and symmetric (2 exs.) presence of A 2, asymmetric absence of A 4 (1 ex.); abdominal tergite VII — absence of Mc (1 ex.); abdominal sternite IV — asymmetric absence of P 1 (1 ex.). Larvae II (39 specimens): abdominal sternite II — absence of Pc (1 ex.); abdominal sternite III — absence of Pc (1 ex.); abdominal sternite VIII — asymmetric absence of seta 1 (1 ex.). Notes. Although the Japanese specimens differ slightly from the original description in the length of foretarsal sensilla b and d (neither apex reaching the base of f in the original description) along with b’ (its apex reaching the base of α 6 in the original description), and in the chaetotaxy of abdominal sternite I in larva II (A 2 absent in the original description). However, these differences represent intraspecific variation. Indeed, there are no substantial differences in the important specific features from the original description. This Gracilentulus species belongs to the “ gracilis ” group, which is recorded from Japan for the first time here. Szeptycki (1993) described the anterior setae on abdominal tergite VII as seven setae (Ac, A 2, A 4, and A 5). Since A 1 setae emerge in the maturus junior, their occurrence was confirmed in 176 females and 39 maturi juniores obtained in the current study. In further analysis, a pair of A 1 setae appeared in 18 females while one A 1 had disappeared with high frequency (Table 4). When one A 1 disappeared, the remaining A 1 was found to move slightly toward the center. Hence, seta Ac in Szeptycki (1993) should be A 1; thus, the anterior setae on abdominal tergite VII should be assigned as eight setae in pairs of A 1, A 2, A 4, and A 5, although A 1 disappears asymmetrically with high frequency. Szeptycki (1993) suggested the possibility of facultative parthenogenesis in G. europaeus. In the present study, 176 adults from two sites were all females. Additionally, at Rishiri Island, all larval stages except for prelarva were obtained, indicating that an alternation of generations is taking place here. This result supports the hypothesis of Szeptycki (1993). Both localities from which the species was obtained in Hokkaido were artificial botanical gardens. In Rishiri Island, surveys were conducted at several sites, including natural forests, but the species was only collected in a botanical garden (Maehara et al. 2003; Nakamura et al. 2011). Although proturans have been collected from more than 560 localities in the main island of Hokkaido (Imadaté & Ohnishi 1993), Gracilentulus species had previously not been obtained. Indeed, the current record from the botanical garden in Sapporo is the only locality at which collection has been successful on the main island of Hokkaido. These results suggest that this species was probably introduced into Hokkaido. Similar examples of out-of-country introduction were reported for Proturentomon minimum (Berlese) and Gracilentulus gracilis (Berlese) in New Zealand by Tuxen (1985). In addition, as stated by Minor (2008), the fact that only females were found is also indicative of out-of-country introduction.

Common Names

No common names available.

Taxonomic Hierarchy

Kingdom: Animalia

Phylum: Arthropoda

Class: Protura

Order: Protura

Family: Acerentomidae

Genus: Gracilentulus

Species: Gracilentulus europaeus Szeptycki, 1993