Pseudachorutes longisetis Yosii, 1961

Babenko, Anatoly, Kuznetsova, Natalia, Nakamori, Taizo & Shveenkova, Yulia, 2021, A review of Pseudachorutes Tullberg, 1871 (Collembola, Neanuridae) from the East Asia, with description of six new species, Zootaxa 4938 (4), pp. 351-391 : 381-383

Pseudachorutes longisetis Yosii, 1961

Figs. 84–89 , 94 , Table 1

P. conicus Lee & Kim, 1984 , syn. nov.

Examined material. Russia: 1 female, Far East, Southern Primor’e, Ussuri State Nature Reserve , Anikin River valley , broadleaf forest (walnut, ash, poplar, etc.) with Pinus sibiricus , 43°40.1’N 132°29.92’E, ~ 150 m alt., 13 August 2017 ; 1 female, same region, but Sikhote-Alin State Nature Reserve , oak forest on gentle slope, 44°58.9’N, 136°32.05’E, ~ 200 m alt., 6 August 2017 ; 2 females (preadult) and 1 juvenile, same Nature Reserve, but Brusnichnaya River , mixed (cedar, poplar, spruce, elm, white fir, birch, etc.) forest in valley, 45°38.9’N 137°0.58’E, ~ 200 m alt., 6 August 2017 ; 2 juveniles, Khabarovsk Territory, Komsomolsk State Nature Reserve, Gorin River , mixed coniferous-broadleaf forest, rotting wood, 50°44.25’N 137°25.43’E, ~ 250 m alt., 10 August 2018 ; 2 juveniles, same region, Anyuinski National Park, Tormasu River , mixed coniferous-broadleaf forest, rotting wood, 49°18.2’N 137°34.2’E, ~ 200 m alt., 07 August 2018. All N. Kuznetsova, A. Kuprin & A. Geraskina leg.

Japan: 1 female, Honshu Island, Nagano Prefecture, E Chino city, Kitayama, surroundings of Mugikusa Hutte, 36°4.13’N 138°20.3’E, 2280 m alt., mixed forest with old trees ( Betula , Abies ) on steep slope, decaying wood, 11 August 2016. M. Potapov & N. Kuznetsova leg.; 1 female, Kyushu Island, Miyazaki Prefecture, Ohkawauchi, Shiiba Village, «Maruju», 32°23.92’N, 131°10.5’E, ~ 1100 m alt., pine litter, 04.08.2016. Nakamori T., Saitoh S., Potapov M., Kuznetsova N. leg.; 1 male, same area, but « Kashiba National Forest», Kashiba, Misato-cho, foot of Mt. Sanpo-dake, 32°21.25’N, 131°12.6’E, ~ 800 m alt., evergreen oak forest, litter, 06.08.2016. Nakamori T., Saitoh S., Potapov M., Kuznetsova N. leg.

South Korea: 1 female, Gangwon-do , upper part of Palsan Mt., oak forest, litter, 09 September 2017 ; 2 juveniles, same region, upper part of Pongnaesan Mt. , oak forest, litter, 06 September 2017. A. Kuprin leg.

Main diagnostic characters: Large to medium sized species with long differentiated setae. Labrum with 0/234 setae, labium with 3 proximal setae and seta L, basomedial part of labium with 4 setae, its basolateral part with only 3 setae, perilabial area with 4 setae. Head with both a0 and d0, Th. I with 4+4 setae, all terga with some additional setae, mucro with basal «swelling». Each anal valve with three hr-setae.

Description based on the examined material. Body length (without antennae) usually about 1.0– 1.3 mm, sometimes up to 2.5 mm. Colour dark, uniform. Tegument granulation not especially coarse and uniform.

Antennae slightly shorter than head, Ant. III–IV fused dorsally, ventral separation well marked. Ant. IV with trilobed apical vesicle, external ms, subapical or and seta i present; dorsal side of Ant. IV with six clearly differentiated, curved sensilla (S1–S4 and S7–S8), ventral file poorly developed consisting of few short setae of various shape. Antennal organ of Ant. III typical, inner sensilla located in cuticular fold ( Fig. 86, 86a ), sgv about as long as sgd, ventral ms present. Ant. I–II with 7 and 12 setae, respectively.

Head with 8+8 ocelli. PAO elliptic, consisting of 8–14 vesicles, its long axis slightly longer than nearest ocellus B, ratio 1.2–1.4: 1. Buccal cone not especially long. Maxilla styliform with small apical tooth, lamellae not clearly seen. Mandible with three almost subequal teeth. Distal edge of labrum rounded, number of labral setae as follows: 0/234 (the number of labral setae can also be interpreted as 2/234. In this case only two setae will remain on the mentum). Main part of labium with three proximal ordinary setae and distal seta L on tiny papilla, labial organites invisible; basomedian part of labium (submentum) with all usual setae, but lateral part (mentum) with only three setae ( Fig. 94 ). Perilabial area with 4+4 setae. Head with 2+2 setae along ventral line as usual for genus.

Dorsal setae long, thin and strongly differentiated in length, sensilla short ( Fig. 84–85 ). Chaetotaxy more or less symmetrical, but abnormalities rather frequent, number of sensilla as usual: 22/11111. Main peculiarities: head with unpaired a0 (often absent in juveniles) and d0, seta Oc2 longer than Oc1 and Oc3, Th. I with 4+4 setae, Th. II–III usually with 1–2 extra setae located further laterally to lateral sensillum, Th. II with lateral ms present. Abd. IV–V with 3+3 axial setae, on Abd. IV setae a1 and p1 shorter than m1, on Abd. V setae a1 and p1 clearly longer than m1. Abd. V with p2 present.

Thoracic sterna without setae. Ventral tube with 4+4 setae, no seta on sternum of Abd. I, Abd. II with 4–6 ventral setae on each side, Abd. III with 8–10 setae. Tenaculum with 3+3 teeth as usual. Furca not especially long. Manubrium with 9–10+9–10 setae on main part, 5 setae on each basolateral lobe and 3–5 basal setae in line. Dorsal side of dens with six setae and uniform granulation, hyaline field on its ventral side about as large as mucro. Mucro long and curved, lateral lamella high and short forming characteristic basal swelling ( Fig. 88 ). Each anal valve with three tiny hr-setae.

Legs I–III with 1, 2–3, 2–3 setae on upper subcoxae, 0, 3, 3 setae on lower subcoxae, 3, 5–7, 7 setae on coxae, 6, 6, 6 on trochanters, 12–13, 12, 10–11 setae on femora and 19, 19, 18 setae on tibiotarsi. Unguis usually long and thin ( Fig. 87 ), with inner tooth in lower half of inner edge and pair of small basal teeth laterally.

Remarks. Pseudachorutes longisetis is an easily recognizable species that appears to be widespread in the region. Unfortunately, our interpretation of this species given above is based on several assumptions and can only be considered as the most probable. Our description of this species does not contradict the original, but, unfortunately, the latter does not meet modern standards. In fact, it postulated that P. longisetis is characterized by long setae, which are clearly differentiated in length, trilobed papilla on antennae, Ant. IV with several dorsal sensilla (up to 8, according to Yosii) and undeveloped ventral file, mandibles with 3 teeth, narrow and long unguis with inner tooth, 6 setae on dens and mucro with a basal lobe. The figure of chaetotaxy given in the original description is rather sketchy. In principle, it is similar to that of our individuals, although Abd. V has only 2+2, and not 3+3 axial setae. Small juveniles studied by us also usually have only 2+2 axial setae on both Abd. IV–V and a1 longer than p1 ( Fig. 89 ). Based on this fact, it can be assumed that setae m1 on Abd. IV are not homologous to those on Abd. V. On Abd. IV, they are likely to be a part of the basic set while shorter setae of a-row are optional. Conversely, short m1-setae on Abd. V most likely appear during ontogenesis. The only real differences between Yosii’s description and our specimens is VT with 3+3 setae, whereas adult specimens in our material always have 4 distal setae on each lobe of VT (3+3 setae can be seen only in juveniles).

Practically the same set of morphological characters listed above is characteristic of two other species, described from the region, namely P. conicus Lee & Kim, 1984 ( South Korea) and P. lishanensis Gao, Yin & Palacios-Vargas, 2008 ( China). Of these, the former is almost impossible to distinguish from P. longisetis based on existing descriptions. The differences between them: about 7 blunt, curved sensory setae on Ant. IV in P. conicus (but only 5 sensilla are shown on fig.2E in Lee & Kim (1984). Most probably that they counted Ant.IV sensilla together with sgd and sgv, as they later wrote that IIIAO consist of two club shaped lobes in a groove and not mentioned guards) vs einigen (bis 8)… Sinnesborsten in P. longisetis, PAO with 13–15 vesicles in conicus vs 10 in P. longisetis , number of maxillary lamellae, 3 in P. conicus vs 1 in P. longisetis , can hardly be considered sufficiently reliable. There is also one difference in chaetotaxy:Abd. V with 3+3 axial setae in P. conicus vs 2+ 2 in P. longisetis . Unfortunately, in both case this is clear only from figures, and therefore needs confirmation. Among three Korean specimens we have seen only one full-size adult female. Its chaetotaxy is identical to those of Japanese and Far Eastern materials and is characterized by the presence of 3+3 axial setae on both Abd. IV–V, whereas juveniles have 3+3 such setae only on Abd. IV. Unfortunately, we have seen no types of both species, but believe that until proven otherwise, it would be wise to treat these species as synonyms.

The specific status of P. lishanensis is also likely to require additional confirmation. Main diagnostic characters of these species are very similar whereas chaetotaxy of P. lishanensis resembles that of juveniles of P. longisetis with two row of setae on all terga from Th. II to Abd. V. Apart from this, unguis in P. lishanensis appears to be not so thin and long.

In addition, at least three more similar species are known in the genus, i.e. P. chazeaui Najt & Weiner 1991 , P. yoshii Najt & Weiner 1991 and P. polychaetosus Gao & Palacios, 2008 . The first two were described from New Caledonia, the latter one—from China (a closely related form was recently found in Japan, see below). All of them clearly form an isolated species group, which differs sharply from other species of the genus. Apart from long differentiated dorsal setae, they are characterized by a similar structure of labium and a distinct tendency toward a polychaetosis, including the presence of additional setae on the thoracic paraterga located laterally to m6 (= S) sensilla and setae p2 on Abd. V which is unusual for the genus. This group also seems to have a fairly well-defined distributional range that encompasses the Russian Far East, China, Korea, Japan, and the South Pacific.

Distribution. The species appears to be widespread in the region being known from Japan to Khabarovsk Territory.

Figures

FIGURES 84–89. Pseudachorutes longisetis Yosii: 84, chaetotaxy of head and Th. I–II; 85, chaetotaxy of Abd. III–VI; 86, inner sensilla of AOIII; 87, tibiotarsus and unguis, leg III; 88, dens and mucro; 89, chaetotaxy of Abd. IV–VI (juvenile specimen). Scales: Figs 84–85 = 0.1 mm, 86–89 = 0.01 mm.

FIGURES 90–94. Pseudachorutes polychaetosus Gao & Palacios-Vargas (90–93) and P. longisetis Yosii (94): 90, chaetotaxy of head and Th. I–III; 91, chaetotaxy of Abd. III–VI; 92, labium; 93, tip of macroseta; 94, labium. Scales: Figs 90–91 = 0.1 mm, 92–94 = 0.01 mm.