Baikalozercon, Marchenko, 2022

Marchenko, Irina I., 2022, Description of new genus Baikalozercon (Acari: Mesostigmata: Zerconidae) with two new species from South Siberia Mountains (Russia), Zootaxa 5120 (3), pp. 301-333 : 302-304

Genus Baikalozercon gen. nov.

Type species: Baikalozercon dracunculus sp. nov.

Other included species: Baikalozercon irbis sp. nov.

Diagnosis. The new genus is based on adult female and male material representing two newly described species. Adults of Baikalozercon are distinguished from those of other genera of the family Zerconidae in a combination of morphological attributes: very large size of idiosoma 900–1000 long; neotrichous dorsal shields; multiple gland pores gv2, dispersed over surface of opisthogastric region including ventri-anal shield; very long peritremes, extending from mid coxa IV to mid coxa I in adults as in deutonymphs; sternal region with some paired or entire fragments of sternal shields; chelicera with suboval area (“window”) with thin cuticle on paraxial side of fixed chela. Female genital shield extends under the lower edge of the posterior sternal shield, which has very specific convoluted structure of cuticle. Male with sexual dimorphism of chelicera and II legs. Male fixed digit of chelicera with extended apical edge and large apical outgrowth; male legs II with some modified enlarged setae on femur, genu, tibia or only on femur.

Etymology. The name of the genus Baikalozercon reflects the name of Baikal Lake in Eastern Siberia ( Russia), because two described species co-occur in mountains of Baikal Region.

Description. Large-sized, bulky body, brownish mites, with pear-shaped idiosoma, divided into two strongly sclerotised shields.

Idiosomal dorsum. Dorsal shields neotrichous, with festoon or tuberculate ornamentation. Anterior margin of podonotal shield curved ventrally to form a vertex. Setae j1 is the longest on podonotal shield, strong, pilose, and inserted on anterior margin of idiosoma; setae z1 inserted on vertex and rx setae on peritrematal shield. Podonotal and opisthonotal shields with four pairs of pore-like structures in each. Median and lateral setae of opisthonotal shield located on elevated areas; areas without setae located in shield depressions with smooth radiate reticulation. Marginal r-R setae slightly curved and feathered, inserted on rounded tubercles. Posterodorsal 5–7 sigillae presented. Posterior part of opisthonotal shield curved on ventral side and fused with ventri-anal shield.

Idiosomal venter. Tritosternum with pair of pilose laciniae free from each other along their entire length. Female sternal region with three separate sternal platelets: first with irregular ragged edges along inner contour, second platelet divided into two small oval fragments. Third platelet large, single, with specific convoluted structure of cuticle, with medial incision in posterior part; surrounded by a hyaline membrane. Female genital shield large, with a pair of internal sclerites, surrounded by a trapeziform hyaline membrane, with mid-anterior incision opposite the same on the third sternal platelet; anterior part of genital shield extends under third sternal platelet. Female with a pair of post-genital sclerites and pair of large metapodal platelets, elongated in horizontal direction. Male sternal region with three or four sternal platelets: some divided into fragments and some entire. Male genital opening located at level between coxae II–III, covered by two sclerites, with a pair of eugenital setae on the anterior sclerite; and a pair of inner sclerites. In both sexes endopodal sclerites present around coxae III–IV; exopodal sclerites fused with peritrematal shields in region of coxae III–IV; peritrematal shields strongly sclerotised, ornamented with festoon reticulation along entire length, fused anteriorly forming a vertex, with six pairs of poroids gp1–gp3, ip1–ip3 and two pairs of short barbed setae: z1 and rx. Peritremes slightly undulating, very long, extending from mid coxa IV to mid coxa I. Gland pores gv2 multiple, dispersed over surface of opisthogastric region including ventrianal shield. Ventri-anal shield broad, fused to opisthonotal shield posteriorly, with festoon reticulation, with 9–15 smooth opisthogastric setae, and marginal rows of opisthonotal pilose setae on rounded tubercles. Anal area with para-anal and post-anal setae; with pair of glands gv3 located antero-laterally of para-anal setae; cribrum extends from ventral to dorsal sides of idiosoma between the posteriormost marginal setae. Anal opening with two pairs of lyrifissures on each valve.

Gnathosoma . Epistome with irregularly serrated lateral edges and smooth, long, bifurcated median projection. Corniculi of moderate size. Internal malae protrude distinctly beyond corniculi; with smooth elongated branches, barbed at base. Setae h1–h3 smooth, attenuate, pc serrated. Deutosternum with seven denticulate rows. Chelicerae large, with long dorsal seta, lateral (antiaxial) and dorsal lyrifissures, serrated arthrodial corona and paraxial suboval area (“window”) of thinner and lighter cuticle layer on fixed digit, pilus dentilis tubular with rounded or bifurcate top. Female fixed digit with seven medium-sized teeth, movable digit with three or four medium-sized teeth in addition to distal hook. Male fixed digit with six or seven teeth and large apical outgrowth, movable digit as in female. Palpal chaetotaxy 2–5–6–13–15, palp with five free segments; palp trochanter with seta al1 long and pilose in distal third, seta al2 short and smooth; palp genu with seta al1 smooth and al2 pilose in distal third; palp tarsal claw two-tined.

Legs. Legs of moderate length. Setae of legs heterogeneous. All legs with sclerotised claws and pulvillus with apically rounded lobes. Pretarsus of legs II–IV with ambulacral stalk, tarsi I with sessile claws. Coxae I with split on dorsal side, coxae IV with recesses on anterolateral side; coxae II–III with antero-dorsal spines: II with large sharp spine, III with small one; coxae IV with alveolar vestige of second av seta. In male legs II with sexual dimorphism in form of enlarged spine-like setae that can be located on femur— al1, al2, av1, on genu al1 and on tibia al1; or only enlarged setae on femur al1, al2. Chaetotaxy of legs I–IV: coxae 2, 2, 2, 1; trochanters 6 (1 1/3 1), 5 (1 1/3 0), 5 (1 1/3 0), 5 (1 1/3 0); femora 13 (2 5/4 2), 11 (2 5/3 1), 6 (1 4/1 0), 6 (1 4/1 0); genua 13 (2 6/3 2), 11 (2 5/2 2), 10 (2 4/2 2), 10 (2 5/2 1); tibiae 14 (2 6/4 2), 10 (2 4/2 2), 9 (2 3/2 2), 10 (2 4/2 2); tarsi I—49 (6 29/9 5), II–IV 18 (3 7/5 3). Chaetotaxy of I–IV legs in general typical for Zerconidae , except for IV tibia wich is given by Halašková (1969) and Sikora (2014) as 9 (2 3/2 2).

Differential diagnosis. Comparisons with related taxa (adults). Based on collections in ISEA there are three early derivate genera of Zerconidae in the mountains of South Siberia: Syskenozercon , Halozercon and Baikalozercon . Syskenozercon is found throughout the Palaearctic, and Halozercon and Baikalozercon inhabit the midlands and highlands of South Siberia. They are probably closely related, sharing relative a number of characters to those genera.

Shared characters of Baikalozercon with related genera Syskenozercon and Halozercon . Dorsal idiosoma: neotrichy of podonotal and opisthonotal shields; there are 4–7 posterodorsal sigillae instead of four sclerotised fossae; marginal r–R setae inserted on tubercles; podonotal shields with four pairs of pores po1–po4 and opisthonotal also with four pairs of pores Po1–Po4; anterior margin of podonotal shield curved ventrally to form a vertex with j1, z1 setae; caudal fusion of opisthonotal and ventri-anal shields.

Ventral idiosoma: sternal region of female and male (male of Syskenozercon unknown) with fragmentary sternal platelets; sternogenital region with normal five pairs of setae; genital shield of female surrounded by hyaline cuticle; tocospermous mating system; genital opening of male (for Halozercon and Baikalozercon ) located at level between coxae II–III, covered by two sclerites, with a pair of eugenital setae on anterior one; expansive peritrematal shields with reticulation along entire length, fused anteriorly with podonotal shield forming vertex; with multiple gland pores gv2 dispersed over opisthogastric surface including ventri-anal shield; gland pores gv3 inserted antero-laterad anal opening; anal opening with two pairs of lyrifissures on each valve, euanal setae absent.

Gnathosoma sharing number characters of the family Zerconidae given by Halašková (1969), Moraza & Lindquist (1998) and Ujvári (2011b): hypostome with four pairs of setae (h1 —the longest, h2 shortest, h3 —middle length, pc —serrated); well-developed internal malae; palps with five free segments; chaetotaxy 2–5–6–13–15, palp trochanter with seta al1 long and pilose in distal third, seta al2 short and smooth; palp tarsal claw twotined; deutosternal groove with 6–7 denticles rows with “phylliform structures” (Ujvári, 2011); chelicerae three segmented, with well-developed teeth on both digits; fixed digit with dorsal seta, dorsal and lateral lyrifissures and pilus dentilis. Internal malae in genera Baikalozercon , Halozercon and Syskenozercon similar in form—smooth and pointed anterior branches versus bifurcate in other Zerconidae .

Legs: chaetotaxy in general typical for Zerconidae , except for tibia IV in Baikalozercon , Halozercon and Syskenozercon with 10 setae (2 4/2 2) compared with 9 (2 3/2 2) in other Zerconidae ( Halašková, 1969; Sikora, 2014). Other characters for these three genera are common: coxae I with split on dorsal side, coxae II with large sharp antero-dorsal spine, coxae IV with alveolar vestige of second seta av (visible in large species of Halozercon and Baikalozercon ); pretarsi of legs I–IV with curved claws, pulvillus and paradactyles.

Differences between Baikalozercon and related genera. Characters based on collections of ISEA as well as by Athias-Henriot (1976), Halašková (1969), Moraza & Lindquist (1998) and Cǎlugǎr (2004 /2006) are presented in Table 1 .