Collohmannia, Sellnick, 1922

Norton, R. A. & Sidorchuk, E. A., 2014, Collohmannia Johnstoni N. Sp. (Acari, Oribatida) From West Virginia (U. S. A.), Including Description Of Ontogeny, Setal Variation, Notes On Biology And Systematics Of Collohmanniidae, Acarologia 54 (3), pp. 271-334 : 315-317

Redescription of Collohmannia and Family Diagnosis

Several diagnoses in the literature relate specifically to Collohmannia ( Sellnick 1922, 1960; Bulanova- Zachvatkina 1975) or to its inclusive familygroup taxa Collohmanniidae ( Weigmann 2006) or Collohmannioidea ( Bulanova-Zachvatkina 1975; Balogh and Mahunka 1983; Sergienko 1994; Norton and Behan-Pelletier 2009). When first proposing the family, Grandjean (1958a) gave no diagnosis. Later ( Grandjean 1969) he proposed Collohmannioidea as new, again without a diagnosis, but by international rule both family-group names were made available in 1958. The fossil genus Embolacarus was proposed as a member of Collohmanniidae ( Norton 2006) , but the described structure of its coxisternum and adanal plate of its type species, E. pergratus Sellnick, 1918 are unlike those of Collohmannia , which indicates the mites may not be congeneric. Until E. pergratus is recollected and carefully examined, the reality of these differences will remain in doubt, so Embolacarus is not considered further here. Therefore, Collohmanniidae and Collohmannioidea are functionally monobasic and their diagnoses can be considered equivalent.

The redescription of Collohmannia and new diagnosis of Collohmanniidae presented below are an extension of that by Norton and Behan-Pelletier (2009) for the superfamily, complemented by our study of C. johnstoni and new observations on C. gigantea . They are consistent with what is known about the fossil C. schusteri and with new, preliminary examinations of four other species that will be treated in a subsequent study, viz. C. asiatica and three new species (one in amber) from Eurasia. Juvenile traits are known only from C. gigantea and C. johnstoni .

Collohmannia Sellnick, 1922 (type species C. gigantea Sellnick, 1922 = C. nova Sellnick, 1932 ). Adult. Dichoid Mixonomata (see Grandjean 1969) with sejugal furrow wide dorsally, narrow ventrally. Large (∼ 1200-2000 µm total length), medium to dark brown, overall shape ovate; convex dorsally, flatter ventrally. Sclerotized cuticle porose throughout, with superimposed imbricate pattern on notogaster and plates of anogenital region.

Prodorsum — Stegasime, with independent aspis, isolated from coxisternum by soft cuticle; in dorsal aspect broadly rounded anteriorly, gradually broadening posteriorly to equal anterior breadth of notogaster; aspis with large, semicircular exobothridial lobe extending ventrally from bothridial region, and internal supporting rib (’nervure’) starting near bothridium and extending obliquely anteroventrad to end as articulating condyle for subcapitulum; entire sejugal border projecting internally to form transverse occipital phragma, connecting exobothridial lobes; with short sagittal apodeme projecting in front of phragma. Bothridial seta tapered or slightly broadened distally, with tight sigmoid bend inside bothridium; bothridium with multiple chambers, including one with several dozen contiguous, sausage-shaped outpockets but without extended brachytracheae or tracheae. Setation normal, with long interlamellar and lamellar seta; two pairs of exobothridial setae on exobothridial lobe. With small porose area posterior to each lamellar seta, appearing as macula in transmitted light.

Notogaster — Convex, elliptical in dorsal aspect, extending well onto somewhat flattened venter; without lateral carinae or suprapleural scissure. With 15 pairs of setae, simple but heterogeneous in size, plus alveolar vestiges of pair f 1; three to five pairs long, flagellate. Opisthonotal gland and normal five pairs of lyrifissures present; gla, ip and seta f 2 clustered laterally; ips located in plicature region. With multiple round or oval porose areas, distinct from general porosity and representing dermal glands; most porose areas at or near base of setae, with size somewhat inversely related to setal size (largest around vestige of f 1, flagellate setae with at most narrow ring of pores around insertion).

Coxisternum — Separated from notogaster and anogenital sclerites by soft cuticle. Divided into four parts by ventrosejugal furrow and nearly complete sagittal furrow; tapering posteriad, with epimere IV only about half as wide as I, such that legs IV unusually close together. Supracoxal region of epimere I with spinose seta eI; that of III with large, triangular dorsal extension.

Anogenital region — Genital plates elongate, appearing subrectangular or tapered at ends, according to view; with 7-9 setae longitudinally aligned on medial margin. Anal plates longer than genital plates; narrow, elongated, lens-shaped as pair; with small lyrifissure ian near anterior margin followed posteriorly by three pairs of aligned anal setae. Blade-like preanal apodeme present, appearing in ventral aspect as subsurface, dark medial line running anteriorly from anal valves. Respective aggenital and adanal plate fused in lateral half, separated medially by oblique incision; aggenital portion broadly rhomboid, similar in length to genital plate and bearing two longitudinally aligned aggenital setae in posterior half; adanal portion tapering posteriorly, bearing three pairs of longitudinally aligned setae. Infolded plicature region between anal and adanal plates with narrow intercalary sclerite and lyrifissure iad. With separate, small porose areas on anal and adanal plates, without separate porose areas on genital or aggenital plates. Ovipositor of female normal, with three pairs of coronal setae; three distal lobes short, each with normal four setae. Spermatopositor of male atypical, similar to ovipositor in length but directed slightly posteriorly when fully extended; with two pairs of coronal setae, both on anterior face; anterior distal lobes partly fused to form U-shaped receptacle for movable, scale-like posterior lobe when retracted; anterior lobes with four pairs of setae, posterior lobe with two pairs.

Gnathosoma — Subcapitulum stenarthric, mentum triangular; pharynx with conspicuous, pigmented ventral sclerite, narrow at attachment to mid-ventral commissure, then broadening posteriorly. Capitular apodeme large, with inverted Vshape in cross-section and scissure along sagittal line. Supracoxal seta of palp spiniform. Lateral lips with three pairs of setae, or 1 distally bifurcated. Rutellum atelobasic, distally broad, with five strong teeth; dorsal face without ciliary brush but with two (usually) hyaline, isotropic spines. Palp five-segmented; setation (trochanter-tarsus) 0-2-1- 3-9(+ ω). Chelicera strong, chelate-dentate; attachment of cheliceral sheath well onto principal segment, basal fifth of which thereby inserted into body; cuticle porose, including inserted portion. Adaxial face with small spicules, well-developed Trägårdh’s organ and lamellated organ; abaxial face with two setae.

Legs — Tubular in general structure; sclerotized cuticle with fine porosity, but setae v’ of femora, genua and tibiae insert eccentrically in small, rounded, luminous porose area similar to those of notogaster. Pretarsal ambulacrum tridactylous, claws similar. Genual pore present on I-III, absent from IV. Tibiae I and II with seta c” present; all tibiae and genua with minute seta d closely coupled to solenidion; tarsus I with 4-6 solenidia. All tarsi with proximal accessory setae in ventral, and usually lateral rows; tarsus I with setae in row c; tarsus I with numerous eupathidia, including s and pairs (p), (pv), (it) and distal members of rows v and c; famulus spiniform with rugose surface. Male tarsus I with or without adaxial hypertrichy of ribbon-like setae. Male leg IV with modified genu, seta v” hypertrophied; cuticle of tibia (also sometimes genu) with or without dense small tubercles (pustules).

Immatures — All juvenile instars with colorless, unsclerotized gastronotic and anogenital regions, contrasting with sclerotized prodorsum, epimeral plates and legs; brownish color of sclerotized cuticle increases with successive instars. Prodorsum truncate anteriorly, with very narrow rostral tectum having convex naso remnant on ventral wall, below rostral setae; lateral rib conspicuous; seta xp inserted posterior to border of exobothridial lobe. Gastronotic region with weakly defined transverse grooves anterior and posterior to setal row e; seta f 1 represented only by vestige, nymphs with enlarged setae distributed as in adult; no porose areas evident, but at least some homologous clusters of glandular cells present. Coxisternum structured as in adult; ClaparŁde’s organ without secondary annulation, protective seta 1c with usual scale-like form. Anogenital region without defined sclerites. Genital papillae large, similar in size; setation of genital valves (proto- to tritonymph) commonly 1-4-7, but latter two numbers variable; two aggenital setae form in deuto- and tritonymph respectively (see Remark 8). No inguinal (transcupular) setae in larva; seta p 1 first forms in protonymph; paraprocts without setae (vestiges may be present) or cupules in proto- and deutonymph (see Remark 9).

Collohmanniidae Grandjean, 1958 . Adult. Large (∼ 1200-2000 µm), dichoid Mixonomata of overall ovate form; sclerotized cuticle porose throughout, with superimposed imbricate pattern on notogaster and in anogenital region. Prodorsum: with isolated aspis; rostrum strongly stegasime; laterally with large exobothridial lobes and posteriorly with internalized occipital phragma; sagittal apodeme and lateral supporting rib present; bothridium with chamber having dense, contiguous outpockets; with pair of porose areas posterior to lamellar setae. Notogaster: with vestigial seta f 1 and 15 pairs of setae, of which 3-5 pairs enlarged, flagellate or nearly so; with many small dermal glands associated with small porose areas, most at or near setal insertions. Coxisternum: epimeres successively more narrow posteriorly; plates divided into four units by sejugal furrow and narrow sagittal furrow; independent from prodorsum, notogaster and plates of genital region. Anogenital region: genital and elongated anal plates almost contiguous; with blade-like preanal apodeme extending anteriorly from anal vestibule; aggenital and adanal plates fused laterally, separated by oblique, narrowly V-shaped incision medially; spermatopositor directed posteroventrally when extended, longer than ovipositor. Gnathosoma: subcapitulum stegasime; rutellum broad, atelobasic, with strong terminal teeth; chelicera robust, chelate-dentate, with Trägårdh’s organ and lamellated organ; palp fivesegmented, with forked distal eupathidium, seta acm independent of solenidion. Legs: ambulacrum homotridactylous; tarsi with numerous accessory setae, including row c on tarsus I; latter with numerous eupathidia; leg IV dimorphic, male with hypertrophied genual seta v”. Juveniles: prodorsum with very weak rostral tectum; gastronotic region unsclerotized; coxisternum structured as in adult; anogenital region without sclerites, proto- and deutonymph with glabrous paraprocts, sometimes bearing vestiges of setae.