Longoseius (Longoseiulus) disparisetus, Mašán, 2022

Masan, Peter, 2022, A new digamasellid mite of the subgenus Longoseiulus Lindquist (Acari, Mesostigmata) from Slovakia, ZooKeys 1131, pp. 59-70 : 59

Longoseius (Longoseiulus) disparisetus sp. nov.

Figs 1-2 , 3-7 , 8-10 , 11

Type material examined.

Holotype female: SW Slovakia, Podunajská Rovina Flatland, Bratislava Capital, Petržalka Settlement, Sad Janka Kráľa Park (48°08'N, 17°06'E), elev. 135 m, 25 October 2020, wood detritus from a cavity in the trunk of an old and freshly felled elm ( Fraxinus sp.), colonised by an unidentified ant species ( Hymenoptera : Formicidae ). Paratypes: five females, with the same data as the holotype. The type material is deposited in the Institute of Zoology of the Slovak Academy of Sciences, Bratislava, Slovakia.

Diagnosis

(female). The presence of three pairs of microsetae (J3, J4, and Z3) on the posterior dorsal shield of the new species is unique and distinctly different from all other known species of the subgenus Longoseius Longoseiulus . Some displacement of J3 toward the bases of J4, making the bases of J3 and Z3 almost transversely aligned, also makes the idiosomal chaetotaxy of Longoseius (Longoseiulus) disparisetus sp. nov. peculiar. Most of the dorsal setae are of approximately equal length in all other congeneric species, with the exception of Z5 and S5, which are conspicuously long in most representatives of the family and are located at the posterior margin of the opisthonotum.

There are other important diagnostic characters for this new species: (1) the absence of dorsal setae r5 (these setae are present on the soft cuticle in females of the related species whose setae Z3 are prominent and moderately elongate), (2) the absence of many leg setae that Lindquist (1975) indicated in his original definition as being present in Longoseiulus species, possibly based on the chaetotaxy of the type species Longoseius (Longoseiulus) longulus . There is one other species of Longoseiulus for which Hurlbutt (1967) originally reported the chaetotaxy of the legs, namely L. (L.) brachypoda . In comparison with the above species, the new species was found to have setal deficiencies in the following leg segments: genu II with eight instead of 11 setae, tibia II with seven instead of 10 setae, tibia III with six instead of seven setae, and telotarsi II and III with 11 instead of 12 setae. For a further comparison of the chaetotaxy of the legs of the new species with those of the subgenus Longoseius Longoseius , see Table 1 .

Description

(female). Dorsal idiosoma (Figs 1 , 8 ). Idiosoma 310-335 μm long and 140-155 μm wide (six measured specimens), narrowly oval, only moderately elongate, rounded anteriorly and posteriorly, suboval, widest in anterior part, at level of anterior ends of peritremes. Dorsal shield completely divided into podonotal and opisthonotal parts, not completely covering the dorsal surface, exposing narrow strips of lateral soft cuticle. Podonotal shield 153-167 μm long and 106-121 μm wide, anteriorly and posteriorly broadly rounded, with smooth and unornamented surface (not considering sigillae, sclerotic nodules, and some fine and very short lines on anterolateral areas), 18 pairs of setae (j1 - j6, z1 - z6, s1 - s6) and two pairs of usually crescent-shaped subsurface sclerotic nodules between setae z5 (the outer pair with larger and more conspicuous nodules than the inner pair of contiguous nodules arranged anteriorly). Two pairs of anterior marginal setae present, namely r3 on peritrematal shields and r4 on soft cuticle between podonotum and peritrematal shields. Opisthonotal shield 147-166 μm long and 76-93 μm wide (excluding lateral strips of scutal elements), anteriorly and posteriorly broadly rounded, laterally straight and nearly parallel, largely smooth except for a small foveolate area between setae Z4, with 15 pairs of setae (J1 - J5, Z1 - Z5, S1 - S5); anterior margin of well-sclerotized part of shield with two deep medial incisions, flanked by narrow band with nearly desclerotized margin. Four pairs of posterior marginal setae present: R1 on soft cuticle adjacent to anterolateral margins of opisthonotum; R3 and R4 on narrow longitudinal bands of scutal elements parallel to lateral margins of opisthonotal shield and narrowly fused to posterolateral margins of shield; R5 usually on soft integument on ventral side near setae JV5 or rarely on margin of opisthonotal shield. All dorsal setae smooth and needle-like, usually similar in length; three pairs of setae (J3, J4, and Z3) conspicuously reduced in length and each formed as a microseta (2-4 μm long); S5 longest (37-48 μm); lengths of other dorsal setae as follows: j1 - j6, z1 - z6, s1 - s6, r4, J1, J2, Z1, Z2, and S1 - S4 = 7-11 μm; J5, Z4, R1, R3, and R4 = 5-7 μm; Z5 = 22-30 μm; r3 and R5 = 10-14 μm.

Ventral idiosoma (Figs 2 , 3 , 9 , 10 ). Tritosternum with short columnar base and two laciniae; laciniae divided to base, each sparsely, finely and shortly pilose. Sternal shield weakly sclerotized and defined (compared to epigynal and ventrianal shields), longer than wide, with two lobe-shaped anterior extensions each bearing a seta (st1), four pairs of sternal setae (st1 - st4), and three pairs of poroidal structures; st3 more closely spaced than the other pairs of sternal setae; posterior margin moderately concave and shaped into posterolateral angles, each bearing a metasternal seta (st4); shield smooth over entire surface, except for small desclerotized areas lateral to st1, each with three to five short lines (Figs 3 , 9 ). Epigynal shield elongate, 81-93 μm long, widest at anterior hyaline part (48-55 μm), formed as convex and moderately trilobate marginal structure, narrowest at level of st5 (27-33 μm), slightly rounded posteriorly, with a pair of genital setae (st5) near posterolateral margins and a pair of genital poroids posterior to st5. Exopodal and endopodal plates or platelets not developed, absent. Peritremes usually with dorsolateral to lateral position on idiosoma (Fig. 1 ), shortened, 67-84 μm long, each with anterior end extending slightly beyond posterior margin of coxa II. Peritrematal shield developed only along anterior part of peritreme (r3 captured by shield), narrowly connected to podonotal shield at level of s3, completely reduced along posterior part of peritreme and weakly developed near stigma, with very short poststigmatic part. A pair of strongly elongated and longitudinally oriented metapodal platelets present; platelets narrow, 34-42 μm long and slightly curved. Ventrianal shield expanded posteriorly, vase-shaped, distinctly longer than wide (69-80 μm long and 49-58 μm wide), with nearly straight anterior margin, broadly rounded posterior margin, smooth surface, four pairs of preanal setae (JV1 - JV3, ZV2) in addition to three circum-anal setae and one pair of gland pores located near posterior margin at level of postanal seta (pa); adanal setae (ad) at least twice as long as postanal seta (ad 18-25 μm, pa 8-12 μm); anus and cribrum relatively small. Soft opisthogastric cuticle with three pairs of preanal setae (ZV1, ZV3, and JV5). Ventral setae similar in form to those on dorsal side of idiosoma, with the following lengths: st1 - st5, JV1 - JV3, ZV1 and ZV2 = 8-11 μm, ZV3 = 5-7 μm, JV5 = 12-16 μm.

Sperm induction system (Fig. 4 ). Sperm duct relatively well sclerotized, long and wide, located within the coxa, trochanter, and femur of legs III, apparently bifurcate near its terminal part, and opened at level of distal part of femur III.

Gnathosomal structures (Figs 5-7 ). Epistome triramous; median process short, thin, straight, usually with obtuse tip; lateral rami conspicuously longer and thicker than median process, each sharply pointed and usually with a small subapical denticle or tine (Fig. 5 ). Hypostomal furrow relatively narrow, with five transverse rows of denticles connected laterally by a line; all transverse rows of denticles uniformly narrow and fifth (most proximal) row not noticeably wider than preceding rows, each row with few (3-7) sparsely to regularly spaced denticles; corniculi horn-like and divergent; internal malae extending beyond corniculi and formed as pointed projections with serrated outer margins (Fig. 6 ). Subcapitular setae smooth and needle-like, h2 shortest and h3 longest. Palptrochanter with five setae, palptarsal apotele two-tined. Chelicerae relatively large (compared to size of gnathosoma or idiosoma), with middle article 68-78 μm long; cheliceral digits dentate, similar in size; movable digit quadridentate, with most proximal tooth largest; fixed digit with 5-8 teeth in addition to terminal hook bearing small subapical tooth, and with minute setiform pilus dentilis (Fig. 7 ); a coronet-like fringe, dorsal cheliceral seta, and antiaxial lyrifissure not discernible.

Legs (Fig. 11 ). All legs with well-developed pretarsus and ambulacral apparatus (including pulvillus and two claws), distinctly shorter than idiosoma: legs I 180-205 μm, legs II 135-155 μm, legs III 105-120 μm, and legs IV 135-160 μm long. Leg segments not spurred ventrally, with smooth and needle-like setae, except telotarsi II-IV with setae ad1, pd1, av1, pv1, and md (when present) shortened and thickened, spine-like, and pd2 thickened. Chaetotactic formulae for each leg segment as follows: leg I - coxa (2), trochanter (6), femur 2-3/1, 2/2-2 (12), genu 2-2/1, 2/2-2 (11), tibia 2-2/1, 3/2-2 (12); leg II - coxa (2), trochanter (5), femur 2-2/1, 1/2-2 (10), genu 1-2/1, 2/1-1 (8), tibia 1-1/1, 2/1-1 (7); leg III - coxa (2), trochanter (4), femur 1-2/1, 1/0-1 (6), genu 1-2/1, 2/0-1 (7), tibia 1-1/1, 2/1-0 (6); leg IV - coxa (1), trochanter (5), femur 1-2/0, 1/1-1 (6), genu 1-2/1, 2/0-1 (7), tibia 1-1/1, 2/1-1 (7). Tibia I without one anterodorsal seta (ad3), tibia III without both posterolateral setae (pl1, pl2), and genua III and IV each with only one ventral seta (pv absent). Basitarsi of legs II and III each with two dorsal setae (al3 and pl3 absent), basitarsus IV with only one dorsal seta (al3, pd3, and pl3 absent). Setation of telotarsi II-III-IV, respectively, 11-11-12 (excluding the pair of dorsodistal seta-like processes); telotarsi II and III each lacking a mediodorsal seta (md), but telotarsus IV with seta md present.

Taxonomic note.

Among the closest relatives with known chaetotaxy of the legs, the new species is easily recognised by the specific number of setae on several leg segments (see Table 1 and the above diagnosis). It lacks many leg setae that Lindquist (1975) indicated in his original definition as being present in Longoseiulus species, namely al, ad3, pl on the genu II; al, ad2, pl on the tibia II; pl on the tibia III; and md on the telotarsi II and III. This requires some amendments to the diagnosis introduced by Lindquist (1975) for Longoseiulus and partially for the genus Longoseius (a pl seta found on the tibia III in Longoseius cuniculus Chant, 1961 is absent in the new species).

Etymology.

The specific name is derived from the Latin words dispār (unequal or dissimilar) and sēta (bristle or hair) and refers to the striking differences in length between the setae on the opisthonotal shield of the female of this new mite (three pairs of setae are greatly reduced and formed as microsetae).

Key to the worldwide species of the subgenus Longoseius Longoseiulus (females)

Longoseiulus includes seven described species, all known from the Holarctic. Only Longoseius (Longoseiulus) aberrans Hirschmann, 1960 is not included in the following key because its description is based solely on the male stage (it is one of the species with 21 pairs of setae on the anterior dorsal surface, including r5). It is not possible to reliably subdivide the individual species of Longoseiulus known to date based on literature data alone, without examining the type specimens. They should be thoroughly revised, redescribed, and compared in future studies to obtain a more accurate and reliable identification key than the one presented in this study. The original descriptions of most Longoseiulus species were not elaborated with the necessary precision (for example, they lack information on the chaetotaxy of the legs or on the measurement of important setal or scutal structures). Therefore, it is not currently possible to define and delimit some species morphologically on the basis of reliable characters. It is likely that a future revision will reveal the conspecificity of some species now placed in this subgenus.

1	Anterior dorsum with 20 pairs of setae, including two pairs of marginal setae on peritrematal shields (r3) or soft cuticle (r4); setae Z3 short (Z3 ≤ Z2, Z3 ≤ j5), never reaching beyond posterolateral margins of opisthonotal shield; idiosoma relatively small, 290-335 µm long	2
-	Anterior dorsum with 21 pairs of setae, including three pairs of marginal setae on peritrematal shields (r3) or soft cuticle (r4, r5); setae Z3 long (Z3 ≥2 × Z2, Z3 ≥2 × j5), reaching beyond posterolateral margins of opisthonotal shield; idiosoma relatively large, 330-390 µm long	3
2.	Three pairs of opisthonotal setae (J3, J4, and Z3) conspicuously shortened, formed as microsetae (2-4 µm long), at least twice shorter than other dorsal setae; inner pair of sclerotic nodules on hexagonal dorsal area with anterior position as outer pair; tibia III with 6 setae (without posterolateral setae)	Longoseius (Longoseiulus) disparisetus sp. nov. [Slovakia]
-	Three pairs of opisthonotal setae (J3, J4, and Z3) never shortened and almost as long as other dorsal setae (except Z5 and S5); two pairs of sclerotic nodules on hexagonal dorsal area in a transverse row; tibia III with 7 setae (with one posterolateral seta)	L. (L.) longulus (Hirschmann, 1960) [Germany]. L. (L.) longuloides Hirschmann & Wiśniewski, 1982 [Ukraine]
3	Ventrianal shield with three pairs of preanal setae (JV1, JV2, and ZV2)	L. (L.) ornatus (Hirschmann, 1960) [Germany]
-	Ventrianal shield with four pairs of preanal setae (JV1 - JV3 and ZV2)	L. (L.) brachypoda (Hurlbutt, 1967) [U.S.A., Louisiana]. L. (L.) ornatosimilis (Shcherbak, 1980) [Russia, Buryat]. L. (L.) nobilis (Barilo, 1989) [Uzbekistan]

Figures

Figure 11. Longoseius (Longoseiulus) disparisetus sp. nov., dorso-ventral habitus of female (photomicrograph). Not to scale.

Figures 1, 2. Longoseius (Longoseiulus) disparisetus sp. nov., female, with symbols for chaetotactic notation of idiosomal setae 1 dorsal idiosoma 2 ventral idiosoma. Scale bar: 50 µm.

Figures 3 - 7. Longoseius (Longoseiulus) disparisetus sp. nov., female 3 sternal shield and adjacent coxa with trochanter of leg II 4 tubular part of sperm access system in proximal segments of leg III 5 epistome 6 gnathosoma, ventral view 7 chelicera, lateral view. Scale bar: 20 µm.

Figures 8 - 10. Longoseius (Longoseiulus) disparisetus sp. nov., photomicrographs of female 8 dorsal idiosoma 9 sternal region 10 ventral idiosoma. Not to scale.