Dendroseius reductus, Mašán, 2020

Masan, Peter, 2020, A new wood-inhabiting mite species of the genus Dendroseius Karg, 1965 (Acari, Mesostigmata, Rhodacaridae) from Central Europe (Slovakia), ZooKeys 984, pp. 49-57 : 49

Dendroseius reductus sp. nov. Figs 1-2 , 3-6 , 7-10

Type material examined.

Holotype female: SW Slovakia, Podunajská Rovina Flatland, Bratislava Capital, Rusovce Settlement, hard-wood flood-plain forest ( Fraxino-Ulmetum carpinetosum ) with poplar ( Populus sp.), 135 m a.s.l., March 7, 2020, detritus from a hollow of old and dying poplar tree. Paratype females: one specimen, with the same data as for holotype; three specimens, the same locality as in holotype, May 19, 2004, under bark of dead poplar tree. The type material is deposited at the Institute of Zoology, Slovak Academy of Sciences, Bratislava, Slovakia.

Description

(Female). Dorsal idiosoma (Figs 1 , 7 ). Idiosoma oblong, regularly oval, widest at medial portion, 315-345 μm long and 195-220 μm wide (N = 5). Dorsal shield completely divided to podonotal and opisthonotal parts, not completely covering dorsal surface, exposing narrow strips of lateral soft integument. Podonotal shield 157-170 μm long and 170-175 μm wide, with smooth medial surface, delicate lateral reticulation, 17-18 pairs of setae (j1-j6, z1-z6, s2-s6, s1 symmetrically or asymmetrically situated on the shield and soft integument, respectively), and two pairs of scleronoduli between setae j5 and j6; outer scleronoduli larger and more conspicuous. Marginal setae r2, r4, r5 and R1 inserted in lateral soft integument, apparently outside the dorsal shields, and humeral setae r3 placed on peritrematal shields. Opisthonotal shield 165-180 μm long and 175-190 μm wide, finely reticulate on whole surface, and bearing 19 pairs of setae (J1-J5, Z1-Z5, S1-S5, R2-R5). All dorsal setae smooth and needle-shaped, mostly similar in their lengths; setae z1 shortest (10-11 μm) and Z5 longest (35-40 μm); the lengths of some selected dorsal setae as follows: j1 16-19 μm, j3 21-23 μm, j5 17-21 μm, r5 24-28 μm, J1-J4 and Z1-Z3 18-23 μm, J5 17-19 μm, Z4 25-29 μm, S1-S4 21-25 μm, S5 27-30 μm, R2-R4 18-20 μm.

Ventral idiosoma (Figs 2 , 9 ). Tritosternum with long columnar base and two long and distinctly pilose laciniae. Presternal area lacking separate scutal elements. Sternal shield oblong, 90-100 μm long, 66-73 μm wide at level of constriction between coxae II, with smooth and weakly sclerotized but well-defined anteriormost portion possessing first pair of sternal setae and reaching level of first pair of lyrifissures (iv1); posterior margin regularly convex and produced to relatively acute angles each bearing a metasternal seta (st4); the shield with fine reticulate pattern on lateral parts, four pairs of sternal setae (st1-st4) and three pairs of lyrifissures, iv1-iv3 (opening of iv1 and iv2 slit-like while iv3 suboval, iv1 with transverse position to the body axis while iv2 oriented longitudinally). Epigynal shield oblong, 50-60 μm wide, hyaline anteriorly (anterior margin obscure and not distinguishable), almost straight or widely rounded posteriorly, bearing one pair of setae (st5) and a pattern of longitudinal lines; genital lyrifissures (iv5) situated on soft integument behind st5, outside the shield. Four slit-like postgenital sclerites close to posterior margin of epigynal shield present. Peritremes shortened, 66-80 μm long, with anterior end reaching slightly beyond posterior margin of coxa II; peritrematal shields well-developed, free from podonotal shield, markedly narrowed behind coxae IV, bearing humeral setae (r3), and adjacent to anterior margin of podonotal shield close to paravertical setae z1 (Fig. 3 ). Three subtriangular exopodal platelets between peritrematal shields and coxae present. Metapodal soft integument with a pair of small irregular platelets having longitudinal position. Ventrianal shield subquadrate, only slightly wider than long (105-115 μm long and 112-130 μm wide), delicately reticulate on whole surface, bearing five pairs of pre-anal setae (JV1-JV3, ZV2, ZV3) in addition to three circum-anal setae, and a pair of marginal gland pores (gv3) more or less aligned with posterior margin of anal opening; adanal setae (ad) apparently longer than postanal seta (ad 27-30 μm, pa 15-17 μm). Soft opisthogastrict integument bearing two pairs of setae (ZV1, JV5). Ventrally situated setae similarly formed as those on dorsal side of idiosoma. The lengths of some selected setae on ventrum as follows: st1 25-28 μm, st2 24-27 μm, st3 22-26 μm, st4 21-24 μm, st5 21-23 μm, JV1 and JV2 18-23 μm, JV5 22-27 μm.

Sperm induction system (Fig. 10 ). Each gonoporus associated with inner posterior margin of coxa IV, together with relatively short and broad duct formed as a club-shaped structure; the duct opening into small hyaline sacculus. Sperm system of both coxae mutually connected with membranous structure (Fig. 10 ).

Gnathosomal structures (Figs 4-6 , 8 ). Deutosternal groove with seven transverse sculptural furrows, six posterior ones with tiny denticles; corniculi horn-like, divergent; internal malae with median projections contiguous and with serrate margins (Fig. 4 ). The lengths of hypostomal setae as follows: h1 17-22 μm, h2 11-14 μm, h3 19-22 μm, pc 21-25 μm; the setae smooth and needle-like. Palp apotele 2-tined. Epistome triramous, with short central and longer lateral branches, each terminally with one to three points; one specimen abnormally with two central branches (Figs 5 , 8 ). Cheliceral digits of similar size, dentate; movable digit with three closely set teeth in addition to distal hook; fixed digit with about seven teeth in addition to apical hook and minute setiform pilus dentilis (Fig. 6 ); a coronet-like fringe, dorsal cheliceral seta and antiaxial lyrifissure not discerned.

Legs. All legs with well-developed pretarsus and ambulacral apparatus (including pulvillus and two claws), shorter than idiosoma: legs I 290-310 μm, legs II 210-230 μm, legs III 180-200 μm, and legs IV 260-285 μm long. Leg segments not spurred ventrally, with normal chaetotactic pattern for the genus: leg I - coxa 0-0/1, 0/1-0 (2), trochanter 1-1/1, 0/2-1 (6), femur 2-3/2, 2/2-2 (13), genu 2-3/2, 2/1-2 (12), tibia 2-3/2, 2/1-2 (12); leg II - coxa 0-0/1, 0/1-0 (2), trochanter 1-0/1, 0/2-1 (5), femur 2-3/1, 2/2-1 (11), genu 2-3/1, 2/1-2 (11), tibia 2-2/1, 2/1-2 (10); leg III - coxa 0-0/1, 0/1-0 (2), trochanter 1-1/1, 0/2-0 (5), femur 1-2/1, 1/0-1 (6), genu 2-2/1, 2/1-1 (9), tibia 2-1/1, 2/1-1 (8); leg IV - coxa 0-0/1, 0/0-0 (1), trochanter 1-1/1, 0/2-0 (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); tarsi II-IV - 18 setae each. Leg setae uniform and similar in length, smooth and needle-like.

Etymology.

The specific name is derived from the Latin word reductus (reduced) and expresses an important feature of the species - an unusual shape of epistome, a fine flat structure situated on upper surface of gnathosoma, with partly reduced central projection on its anterior margin.

Taxonomic notes.

The triramous epistome of the new species, with remarkably shortened central projection, is unique and quite unlike any other known species in the genus Dendroseius . In other congeners, this central projection is much longer and more acuminate in the terminal part, reaching to (in D. amoliensis ) or slightly beyond the level of the adjacent lateral apices (in all other congeners, including two species exclusively based on deutonymphs and not included in the key below). Nevertheless, the new species is most similar to D. vulgaris distributed in China ( Ma, Ho and Wang 2014), and it can be distinguished from D. vulgaris and other species by the character states presented in the identification key below. Some metric data for D. reticulatus provided in the key are derived from specimens in author’s personal collection from Wales, UK (Anglesey, Newborough Beach, found in decomposing plant substrate in a sandy coastal area). The morphological data used for other Dendroseius species were based only on the original descriptions.

Figures

Figures 1, 2. Dendroseius reductus sp. nov., female, with setal notation of idiosomal setae 1 dorsal idiosoma 2 ventral idiosoma. Scale bar: 50 µm.

Figures 3 - 6. Dendroseius reductus sp. nov., female 3 peritrematal shield and adjacent exopodal platelets 4 ventral gnathosoma 5 epistomes, normal form and an aberration having two central prongs 6 chelicera, lateral view. Scale bars: 50 µm (3), 25 µm (4), 20 µm (5, 6).

Figures 7 - 10. Dendroseius reductus sp. nov., photographs of female 7 dorsal idiosoma 8 epistome 9 ventral idiosoma 10 sperm induction system. Not to scale.