Mycomelichares reductus Mašán & Joharchi, 2021

Mašán, Peter, Joharchi, Omid & Abramov, Vladimir V., 2021, A new genus and two new species of melicharid mites (Acari: Mesostigmata) associated with wood-decaying fungi and mycophagous erotylid beetles (Coleoptera: Erotylidae) in Europe, Zootaxa 4980 (1), pp. 157-173 : 167-172

Mycomelichares reductus Mašán & Joharchi sp. nov.

( Figs 18–32 )

Type material examined

Holotype female: W Russia, Tula Region, vicinity of Suvorov Town (54°07‘N, 36°30‘E), on Tritoma bipustulata Fabricius ( Coleoptera : Erotylidae ), August 14, 2019, lgt. V. V. Abramov. Paratypes: nine females, with the same data as for holotype. All specimens are deposited in the collection of the acarological collection of the Tyumen State University, Museum of Zoology, Tyumen, Russia (TUMZ).

Diagnosis (Female)

Idiosoma oval, oblong, with legs shorter than dorsal shield. Dorsal shield with 38 pairs of setae, 21 pairs on podonotal (j1–j6, z2, z4–z6, s1–s6, and r3–r6) and 17 pairs on opisthonotal portion (J1–J5, Z1–Z5, S2–S5, R2, and R4); setae z1, z3, R1, R3, and R5 not expressed, absent. Tritosternum robust, brush-shaped. Metasternal setae (st4) and associate lyrifissures (iv3) situated on soft integument. Peritremes long, with anterior ends reaching close to paravertical setae (z1). Anus small. Ventral surface of hypostome with seven transverse rows of denticles; anteriormost rostral setae h1 longest, thickened basally and slightly spatulate distally; other setae on hypostome needle-like. Cheliceral digits with robust and sharp denticles; fixed digit with usually 5–7 denticles in addition to bidentate terminal hook. Epistome with smooth anterior margin. Gnathosomal corniculi horn-like,with apparently adjacent and convergent apices. Palp apotele 2-tined. Most leg segments strongly hypotrichous.

Description (Female)

Dorsal idiosoma ( Figs 18 , 27 ). Idiosoma oval, up to 280 μm in width, not completely covered by dorsal shield; the shield narrowly oval, oblong, 440–460 μm long and 235–245 μm wide (n=10), completely and densely reticulate except small area behind setae J4, bearing 38 pairs of setae. Except longest setae Z5 (64–69 μm), longer posterior setae Z3 and S4 (both 35–40 μm), and shortest J5 (12–15 μm), all dorsal shield setae similar in size and form, simple, needle-like and short; lengths of some selected setae as follows: j1–j6, z5, s1 r2 21–25 μm; z2, s2–s5, r4, r5 24–27 μm; z4 30–33 μm; z6, s6, r6 18–21 μm; r3 28–30 μm; J1–J3, Z1, Z4, S1–S3, S5 16–22 μm; J4, R2, R4 14–18 μm; Z2 24–27 μm.

Ventral idiosoma ( Figs 19 , 28 ). Tritosternum robust, with columnar base and thickened laciniae, laciniae proximally fused, distally with dense pilosity, brush-shaped. Presternal region weakly transversely striate and sclerotised, with a pair of elongate, obliquely oriented and indistinct platelets. Sternal shield slightly wider than long, 87–91 μm long and 96–100 μm wide between coxae II, reticulate throughout; reticulate pattern predominated by transverse lines; anterior margin with slight medial concavity, posterior margin slightly concave; shield with two pairs of lyrifissures (iv1, iv2) and three pairs of similar setae (st1 24–26 μm, st2 21–23 μm, st3 27–29 μm). Metasternal setae (st4) and genital setae (st5) shorter than those on sternal shield, 16–19 μm long; st4 together with associated lyrifissures (iv3) situated on soft integument (metasternal platelets absent). Endopodal plates between coxae III–IV well developed, with narrow anterior ends reaching well beyond the level of st3. Epigynal shield oblong, wider in anterior portion, moderately constricted at level of genital setae (st5), tongue-shaped, 143–158 μm long, 73–85 μm wide in anterior and 58–65 μm in posterior portion (st5–st5 53–61 μm), hyaline and widely convex anteriorly (hyaline part not reaching posterior margin of sternal shield), slightly curved posteriorly, bearing one pair of setae and a pattern of reticulation; genital lyrifissures (iv5) situated on soft integument behind st5. Peritremes well developed, long and relatively wide (mainly in their posterior sections), with anterior ends reaching the level of setae j2; peritrematal shields reduced to short poststigmatic parts tapered terminally, and free or narrowly fused to exopodal plates. Soft integument behind coxae IV with a pair of small and elongate metapodal platelets, and one pair of small narrow sclerites. Anal shield ovoid, narrowly rounded anteriorly, almost straight posteriorly, 92–96 μm long and 70–76 μm wide, usually with transverse sculptural lines, three circum-anal setae, and a pair of marginal gland pores (gv3) at level of posterior margin of anal opening; postanal seta longer than adanals (pa 26–33 μm, ad 17–21 μm); anus small, 22–27 μm long and 13–16 μm wide, with almost central position on the shield. Soft lateral and opisthogastrict integument bearing normally eleven pairs of setae (JV1–JV5, ZV1–ZV5, UR), submarginal setae at level of coxae IV absent; opisthogastric setae simple and needle-like (JV1 and JV2 16–19 μm, JV5 36–40 μm, ZV1 11–13 μm).

Sperm induction system. Not discernible.

Gnathosomal structures ( Figs 20–22 , 29–32 ). Anterior margin of epistome convex, smooth ( Figs 21 , 31 ). Venter of hypostome with seven transverse rows of denticles: anterior four rows each with several denticles, fifth and sixth rows widened and each with at least 20 denticles, seventh row with about ten denticles; corniculi horn-like, with adjacent and convergent apices; internal malae with tips reaching slightly beyond corniculi ( Figs 20 , 29 ). Anterior rostral setae (h1) thickened, with distal spatulate portion, other rostral setae simple and needle-like (h1 31–35 μm, h2 14–18 μm, h3 23–26 μm, pc 22–25 μm). Median article of chelicera 75–79 μm long; cheliceral denticles well-developed, robust and sharp, directed forward; fixed digit normally with seven denticles in addition to terminal bidentate hook (seen in dorsal or ventral view), movable digit with three denticles and terminal hook ( Figs 22 , 32 ).

Legs ( Figs 23–26 ). All legs with well-developed pretarsus and ambulacral apparatus (including pulvillus and two claws), shorter than dorsal shield, legs I somewhat longer than legs IV: legs I 340–365 μm, legs II 265–290 μm, legs III 255–280 μm, legs IV 335–355 μm long. Leg chaetotaxy pattern with most segments strongly hypotrichous, as follows: leg I – coxa (2), trochanter (6), femur 2 3/1, 2/2 2 (12), genu 1 3/1, 2/1 2 (10), tibia 2 2/1, 2/1 2 (10); leg II – coxa (2), trochanter (5), femur 1 3/1, 2/1 1 (9), genu 1 2/1, 2/0 1 (7), tibia 1 1/1, 2/1 1 (7); leg III – coxa (2), trochanter (5), femur 1 2/1, 1/0 1 (6), genu 1 2/1, 2/0 1 (7), tibia 1 1/1, 2/1 1 (7); leg IV – coxa (1), trochanter (5), femur 1 2/1, 1/0 1 (6), genu 2 2/1, 3/0 1 (9), tibia 1 1/1, 2/1 1 (7). Leg setae smooth and mostly needle like, as in Figs 23–26 .

Etymology

The specific name is derived from the Latin word reductus (reduced) and expresses an important feature of the species—an unusual and strong reduction of leg setae in comparison with its congeners, and most other members of Melicharidae .

Taxonomic and ecological notes

Diagnostic character states for Mycomelichares reductus are the absence of dorsal shield setae z1, z3, R1, R3 and R5 and reduction of many of leg setae normally developed in most of Melicharidae (only a member of the monobasic genus Mycolaelaps Lindquist, 1995 from North America has similar strong reduction of leg setation). This species has the R- setae considerably reduced, with only two pairs expressed (R2, R4) and placed on the posterior lateral margins of the dorsal shield. Among the proposed species groups of the new genus (see a note above or the identification key below), M. reductus should be considered as a species with a separate position between the Proctolaelaps -like species of the cyllodi group having their R- setal rows completely expressed and with R1−R4 on the opisthonotal portion of the shield, and the Mycomelichares polypori , constituting the most specialised monobasic species group characterised by the R- setal rows completely situated on the soft integument, outside the shield.

Mycomelichares reductus has been found as a phoretic associate of the erotylid beetle Tritoma bipustulata . This host species was considered to be a specific phoront for its congeneric mite Mycomelichares slovacus , described on the base of specimens from the same host in Slovakia ( Mašán, 1998). Apparently, in different geographical areas of its distribution, T. bipustulata can serve for dispersal to various mites with similar ecological requirements.

Figures

FIGURES 18–22. Mycomelichares reductus sp. nov., female: 18. Dorsal idiosoma; 19. Ventral idiosoma; 20. Ventral gnathosoma; 21. Epistome; 22. Chelicera, female, lateral view of distal part.

FIGURES 23–26. Mycomelichares reductus sp. nov., female: 23. medial segments of leg I (trochanter, femur, genu, tibia); 24. leg II (except coxa); 25. leg III (except coxa); 26. leg IV (except coxa).

FIGURES 27–32. Mycomelichares reductus sp. nov., female: 27. Dorsal idiosoma; 28. Ventral idiosoma; 29. Ventral gnathosoma; 30. Palp; 31. Epistome; 32. Chelicera, lateral view.