Acerentulus apuliacus Rusek & Stumpp 1988

Acerentulus apuliacus Rusek & Stumpp, 1988

Figs. 1‒22, Tables 1, 2

Acerentulus apuliacus Rusek & Stumpp, 1988:153

Material examined. Type specimens not available. Examined material: 4 males, 19 females, 4 pre-imagos, 13 maturus juniors and 2 larvae II from litter (feuilles mortes) collected west of Rionero in Vulture (Potenza Province, Basilicata, Southern Italy), 600 m elev., 25 August 1983, coll. S. Vit; 1 male and 1 female collected from litter at the base of a maple (Litiére /pied pourri d’Acer) in Vieste (Foggia province, Apulia, Southern Italy). These specimens deposited in the collection of Geneva Natural History Museum.

Redescription. Body length 1149 ± 125 µm (range: 904–1366; n = 23). Head 135 ± 13 µm long (range 119–182; n = 24); setae sd4 and sd5 present, seta d6 (Rusek et al. 2012) absent (Fig. 1). Rostral setae r1 and r2 nearly 10 µm long, labral seta lb 1.5 times longer than rostral setae (Fig. 2). Single frontal pore anterior to level of pseudoculi (Fig. 3). Rostrum very short. Pseudoculus slightly elliptic, 9 µm long (range: 8‒11; n = 24), longitudinally divided (Fig. 4); PR = 14.6 (range 12.2–18.2, n = 23). Proximal part of maxillary gland long and terminally dilated (Fig. 5), length 26 µm (range: 22–32; n = 23), CF = 5.2 (range: 4.3–6.3; n = 22). Maxillary palpus with slender setaceous sensilla (Fig. 6). Labial palpus with distinctly thickened sensillum (Fig. 7).

Foretarsus length 88 ± 3 µm (range: 78–92; n = 22), claw 24 µm (range: 22–26; n = 18), without inner tooth, TR = 3.6 (range 3.4–4.0; n = 18); empodium length 5 µm (range: 4–6, n = 10), EU = 0.19 (range 0.16–0.24, n = 10); S-shaped seta longer than claw, 28 µm (range: 25–32; n = 10). Sensillum t1 claviform, BS = 0.35 (range 0.27–0.42, n = 22); t2 thin, t3 proximally dilated. Sensillum a long, distinctly broadened basally, passing base of seta γ3; sensilla b‒g slender, long; b, c and d of equal length; sensilla b and c reaching the base of e, sensillum d reaching the base of f, sensilla e and f almost of equal length, not reaching the empodium, sensillum g passing the base of claw, f nearer to e than to g (Fig. 8). Sensillum a’ broad, barely reaching the base of b’, b’ and c’ almost of equal length and thin, the apex of c’ reaching the empodium (Fig. 9). Ventral seta β1 very short, barely reaching the base of δ2; δ4 situated more proximally than sensillum c’. Foretarsal pores present near the bases of sensilla c and g (Fig. 8). Middle tarsus length 37 µm (range: 34–39; n = 20); claw length 17 µm (range: 14–19; n = 20). Hind tarsus length 41 µm (range: 39–44; n = 20); claw length 17 µm (range: 14–20; n = 18).

Thoracic tergite I (Fig. 10) with two pairs of setae (ratio of setae 1: 2 = 2.77:1; range 2.18‒4.00; n = 16) (Table 1). Thoracic tergites II and III (Fig. 10) each with two pairs of anterior setae (A2, A4); setae P1a and P2a very short; seta P2a nearer to P3 than to P2. Seta P5 very short. Length ratio of setae P1: P2 on mesonotum as 1:1.31 (range 1.15–1.43, n = 18). Tergites I–V each with three pairs of anterior setae (A1, A2, A5); tergites II‒V lacking setae P1a and P3a. Seta A4 present on tergites VI‒VII. Seta P3 on urotergites II‒VI anterior to line P2‒P4 (Fig. 11). Tergite VIII (Fig. 12) with 3 pairs of anterior setae (A2, A4, A5); P1a absent. Tergites IX and X with 12 setae; tergites XI and XII with 6 and 9 setae, respectively (Fig. 10, Table 1). Prosternum (Fig. 14) formula 4 + 4 / 6, mesosternum and metasternum (Fig. 15) formulae typically 5 + 2 / 4 and 7 + 2 /4, respectively. Sternites I–VII with 3 anterior setae (Figs. 16‒17); sternites VIII‒X with 4 setae; sternites XI and XII with 6 setae (Fig. 18).

Thoracic tergites II and III (Table 2) with sl pores; al pores on mesonotum. Tergites I‒VIII with psm pores, on tergite VIII opening between two small pointed teeth; al pores on tergites II‒VII; psl pores on tergites VI‒VII (Fig. 11). Tergite XII with ac pore (see Galli & Capurro, 2013, Fig. 12). Thoracic sternites and abdominal sternites I‒II without pores. Sternite III with an asymmetrical spsm pore near the base of a seta P1a (10 adults); in four adults such pore is nearly medial, in three adults two symmetrical spsm pores present. Sternites IV‒VI with symmetrical spsm pore near the base of seta P1 (Fig. 16); spm pore far from posterior margin on sternite VII (Fig. 17); sternite XII with sal pores (see Shrubovych, 2014— Fig. 18).

Imago and Pre-imago Maturus Junior Larva II

Formula Complementary Setae Formula Complementary Setae

Dorsal

Connecting lines on anterolateral corners of sternites IV–VI absent. Pleural pectines weakly developed (Fig. 19). Abdominal appendages II and III with long subapical seta and two setae, one lateral-apical and the other median-apical; comb VIII with 8–9 long teeth (Fig. 13). Penis with 6 + 6 setae (Fig. 20). Female squama genitalis with three spines on each acrostylus (Figs. 21‒22).

Chaetotaxic variation infrequent; asymmetrical shift of seta P1 towards P2 on abdominal tergite I (one adult); symmetrical absence of seta A4 on tergite VI (one maturus junior); symmetrical absence of seta A1 on tergite VII (one maturus junior); presence of seta Ac rather than setae A1 (formula 7/16) on tergite VII (one adult); symmetrical absence of seta A4 on tergite VI (one maturus junior); absence of seta Pc (formula 3/4) on sternite III (two adults – this arrangement may be the chaetotaxy of the holotype – see Rusek & Stumpp 1988); presence of seta Ac rather than setae A1 (formula 3/2) on sternite VIII (one adult); sternite XI with only two setae (one maturus junior).

Pre-imago. Length of body 967 µm (range 797‒1130; n = 4), head 113 µm (range 105‒121; n = 4), foretarsus length 75 µm (range 70‒79; n = 4), TR = 3.0–4.1, BS = 0.34–0.43. Chaetotaxy (Table III) identical to that of adults.

Maturus junior. Length of body 973 ± 123 µm (range: 787–1121; n = 12), head 114 ± 11 µm (range: 98–138; n = 11), foretarsus length 73 ± 6 µm (range: 63–88; n = 12), TR = 3.5‒4.2, BS = 0.23‒0.55. Chaetotaxy (Table III) differing from that of adults in presence of seta Pc instead of setae P1 on tergite VIII.

Larva II. Two specimens: length of body 800 µm, head 91 and 98 µm, foretarsus length 58 µm, TR = 3.4. Chaetotaxy is shown in Table III.

Distribution. Southern Italy: previously known only from the type locality in Apulia (a beech forest on N slope in Bosco Sfilzi, 10 km south of Vico del Gargano, Foggia province). The new material (see above) was collected in another locality of Foggia province (Apulia) and in Basilicata.

Diagnosis and discussion. Due to the long foretarsal sensillum a and to sensilla b and c having the same length, A. apuliacus belongs to the confinis group of Acerentulus. A key to the species of this group can be found in Shrubovych et al. (2012). Rusek & Stumpp (1988) considered A. apuliacus to be related to A. exiguus Condé, 1944, differing from it in the presence of seta A1 on tergite VII, thickened foretarsal sensillum a (slender in A. exiguus), equal lengths of sensilla b and c (the former being shorter in A. exiguus) and the number of spines on the acrostyli (three in A. apuliacus and two in A. exiguus).

A more recently described species from France, Acerentulus charrieri Shrubovych, Schneider & D’Haese, 2012, is close to A. apuliacus. Both species have 8 anterior and 16 posterior setae on Tergite VIII (including seta P1a and lacking P3a) and they share a similar general morphology of foretarsus (position and relative sizes of sensilla). Acerentulus charrieri differs from A. apuliacus in having a significantly longer foretarsus (125‒130 µm), slender foretarsal sensilla a and a’, sensillum b longer than c and distal position of seta δ4.