Opilioseius, Lindquist, Evert E. & Moraza, Maria L., 2010

Lindquist, Evert E. & Moraza, Maria L., 2010, Revised diagnosis of the family Blattisociidae (Acari: Mesostigmata: Phytoseioidea), with a key to its genera and description of a new fungus- inhabiting genus from Costa Rica, Zootaxa 2479, pp. 1-21 : 4-14

Opilioseius , new genus

( Figs 1–29 , 32–35 , 39, 40 )

Type species: Opilioseius grallator new species. Monotypic.

Diagnosis. Among the genera of Blattisociinae, adults of Opilioseius are most similar to those of Aceodromus in sharing the following apomorphic attributes: dorsal shield hypotrichous, lacking podonotal setae z1, z3, z6, r2 and opisthonotal setae J1-J3, S1; genua of legs II and III with 10 and 8 setae, respectively, lacking pv -1; female ventrianal shield weakly sclerotized, with 2, 3, or 4 pairs of opisthogastric setae plus the circumanal setae; female spermatheca with weakly sclerotized calyx. They are distinguished apomorphically from those of Aceodromus and other blattisociine genera by the following attributes: idiosomatic dorsum lacking paravertical lyrifissures idj1, lacking opisthonotal setae Z2, S1, S2, and having the r -R marginal series reduced to just four pairs in females, three of which on soft cuticle, and to two pairs in males, none of which on soft cuticle; peritremes shortened, not reaching to the vertex area; legs I to IV greatly elongated, with I and IV two to three times as long as dorsal shield, and with tarsi II to IV over three times as long as the respective tibial segments; movable cheliceral digit with five teeth and, more basally, with a series of indentations to accommodate the basal teeth of the fixed digit; movable digit with two groove-like structures on its ventroparaxial surface. In contrast, adults of Aceodromus are apomorphic in lacking podonotal setae j1, s1, s2, s5; plesiomorphic differences include females retaining eight pairs of r -R marginals, including seven pairs on soft cuticle (undescribed males have two pairs, of which one pair on soft cuticle, EEL, personal observation); peritremes fully developed, their apices nearly contiguous in vertex area, legs I to IV are subequal to at most 1.5 as long as dorsal shield, and with tarsi II-IV 1.5 to 2.8 times as long as respective tibial segments; movable cheliceral digit quadridentate, lacking basal indentations and lateral groove-like structures.

Description. Idiosomal dorsum. Adult female ( Fig. 12 ). Dorsal shield entire, without lateral incisions, lightly sclerotized, surrounding soft integument smoothly striate. Dorsal shield with complement of 23 pairs of setae, including 15 podonotal pairs (j1-j6, z2, z4, z5, s1, s2, s4-s6, r3) and eight opisthonotal pairs (J5, Z1, Z3-Z5, S3-S5); setae attenuate, of widely disparate lengths, J5 shortest, j6, z2, z5 short, s5 longest, Z3-Z5 nearly as long; most setae smooth, but J5 minutely barbed. Dorsal shield with complement of 18 pairs of discernible pore-like structures (eight podonotal, ten opisthonotal), of which seven pairs (four podonotal, three opisthonotal) superficially appear secretory (gland pores) and 11 pairs (four podonotal, seven opisthonotal) non-secretory (poroids). Soft surrounding cuticle with only three pairs of r-R marginal setae and pair of marginal poroids idRp. Peritrematal plates narrowly uniting with dorsal shield anteriorly to level of setae s1; peritremes shortened, not reaching to vertex area.

Adult male ( Fig. 32 ). Dorsal shield setation, ornamentation, and form as in female except more expanded anterolaterally so as to bear setae r5 and be more broadly united to peritrematal shields at level between setae r3 and z4. Form and proportionate size of dorsal shield setae as in female. Lateral soft cuticle without any R - marginal setae. Peritremes as in female.

Idiosomal venter. Adult female ( Fig. 16 ). Tritosternum with laciniae free for most of length, their fused bases with an obliquely lined series of denticles ( Fig. 5 ). Ventral shields unornamented, weakly sclerotized. Presternal region with weakly developed platelets confluent with sternal shield. Sternal shield entire, with weakly developed endopodal extensions between coxae I-II and II-III, and with three pairs of setae and two pairs of lyrifissures; setae st4 on metasternal plates; sternal lyrifissures iv3 absent ( Fig. 16 ). Endopodal strips between coxae III and IV free, weakly defined. Epigynal shield with its rounded, hyaline anterior margin between legs III–IV not overlapping posterior edge of sternal shield, its posterior margin truncate; setae st5 on shield’s posterolateral margins, paragenital poroids iv5 on soft cuticle. Opisthosomatic venter without discernible metapodal and postgenital platelets; soft integument with seven pairs of setae and three pairs of poroids. Ventrianal shield small, with two pairs of opisthogastric setae and the three circumanal setae; paranals inserted at level slightly anterior to posterior edge of anus, and similar in size to postanal seta; ventrianal shield with a pair of gland pores on posterolateral margins, and a well-developed cribrum behind level of postanal seta. Peritrematal shield with two poroids and one gland pore in area behind stigma where connecting with exopodal strip curving behind coxa IV ( Figs 15, 16 ); peritrematal shield continuous alongside coxae II-IV but without exopodal extensions between bases of coxae II-III and III-IV; shield with weakly developed gland pore anterior to apex of peritreme ( Fig. 12 ). Spermathecal apparatus of phytoseiid-type, with a minor duct emanating from embolus near base of calyx ( Fig. 14 ).

Adult male ( Fig. 33 ). Tritosternum and presternal area as in female. Ventral shields unornamented, weakly sclerotized. Sternitigenital shield with five pairs of setae and two pairs of poroids (iv3 absent), deeply incised between sternal and genital sections, and lacking endopodal extensions between coxae I and II. Endopodal strips between coxae II and III, III and IV free, weakly defined. Opisthosomatic venter without discernible metapodal platelets; soft integument lacking setae and discernible poroids. Ventrianal shield small, with four pairs of opisthogastric setae and the three circumanal setae; attributes of circumanal setae, gland pores, and cribrum as in female. Posteriorly, peritrematal shield and peritreme as in female.

Gnathosoma. Female & male. Gnathotectum with convex, denticulate anterior margin ( Figs 11 , 28 ). Chelicerae of moderate length, without any conspicuous process along antiaxial or paraxial lateral surfaces basal to the digits; fixed digit with tiny, setiform pilus dentilis and row of coarse teeth along entire length of masticatory surface and an offset tooth (gabelzahn) subapically ( Figs 8, 10 , 25 ); movable cheliceral digit of female with a row of several coarse teeth, and with two fine paraxial grooves running proximally and ventrally from the bases of subapical teeth; arthrodial envelope fringed ( Figs 8-10 ); movable digit of male with teeth restricted to basal half of masticatory surface, and with short, bilobate spermatodactyl ( Figs 25–27 ). Paralabral processes simple, acute ( Fig. 4 ). Corniculi normal in form, well separated, more splayed in male ( Fig. 29 ) than in female ( Fig. 1 ), with salivary styli appressed to dorsal cornicular faces and difficult to discern ( Figs 2, 3 ); internal malae fimbriated laterally. Deutosternum with seven transverse rows of denticles, anterior five rows similarly moderately wide and multidenticulate, sixth and seventh rows more widened and denticulate, all rows connected except the seventh ( Figs 1 , 29 ). Subcapitular setae similarly smooth, attenuate, capitular pair pc longer than hypostomatic pairs hp1-hp3. Palpi with normal setation as described for Gamasina by Evans (1964); palpfemoral seta al spatulate, palpgenual setae al -1 and al -2 more or less spatulate; palptarsal apotele two-tined ( Figs 6–7 ).

Legs. Female & male. Legs I to IV with elongated pretarsi bearing paired small claws, paradactyli, and rounded pulvillae ( Fig. 22 b). Legs elongate, especially I and IV, which two to three times as long as dorsal shield ( Fig. 39 ); legs II to IV with tarsus three to four times as long as tibia ( Figs 21 , 39 ). Distal margins of coxae I-IV lacking prominent serrations or spur-like processes. Tarsus I with sensilla S slightly lanceolate apically ( Fig. 24 ), and without markedly elongated setae apically. Tarsi II–IV with apical setal processes ad -1, pd -1 short, about 1/10th as long as pretarsi, and with slender, acute apical process ventrally ( Figs 21, 22 a). Complement of setae on segments of legs I-II-III-IV normal for Blattisociinae as presented by Lindquist & Evans (1965): coxae, 2-2-2-1; trochanters, 6-5-5-5; femora, (2 3/1 2/2 2) - (1 3/1 2/2 1) - (1 2/1 1/0 1) - (1 2/0 1/1 1); genua, (2 3/1 3/1 2) - (2 3/1 2/0 2) - (2 2/1 2/0 1) - (2 2/1 3/0 1); tibiae, (2 3/1 3/1 2) - (2 2/1 2/1 2) - (2 1/1 2/1 1) - (2 1/1 3/1 2); femur II lacking al -2; genu I and tibia I each lacking av -2; genua II and III each lacking pv -1 ( Figs 17-21 ). Leg setae collectively smooth, attenuated, some elongated on tibia III, femur IV, and especially on genu, tibia and tarsus of leg IV. Legs of male without dimorphically modified setae.

Etymology. The name of the genus is a Latinized combination of the term opilio, meaning “shepherd” and applied to the arachnid order Opiliones whose members are typically long-legged, and seius or sejus, a Roman surname (also meaning “divine” or “a wanderer”, according to Chant & McMurtry 1994) used by many authors to form names for genera of mesostigmatic mites. The name is masculine in gender, and is intended to refer to the remarkably long-legged form of these mites.

Distribution and habitats. This monobasic genus is based on material associated with perennial fungal growths on decaying logs from just one locality in coastal lowland rainforest of Costa Rica.

Remarks. The genus Opilioseius is based on several apomorphies, four of which appear to be unique among the known taxa of Blattisociidae : (1) absence of paravertical lyrifissures idj1 on the idiosomatic dorsum; (2) great elongation of legs I to IV, and especially of the tarsal segments of legs II to IV; (3) reduction in size of the male ventrianal shield; and (4) groove-like structures on the paraxial surface of the movable digit of the chelicera. However, the uniqueness of the cheliceral structures at the genus level is problematic, as we have observed bizarrely modified cheliceral digits among various undescribed species of Lasioseius found on bracket fungi, including some that coexist with Opilioseius .

The apomorphic similarities shared between Opilioseius and Aceodromus , as given in the diagnosis and key, are all subject to homoplasy and may be convergences, as members of these two genera are adapted to very different habitats and substrates. While those of Opilioseius are restricted to perennial fungi on decaying logs, members of the four species of Aceodromus known to us (two of them undescribed) occupy herbaceous and grassy habitats, where they may be associated with copiphorine tettigoniids, on which they are phoretic as adult females ( Lindquist & Chant 1964, Lindquist & Evans 1965). Opilioseius grallator is not known to be phoretic, and it is difficult to envisage phoretic behavior among mites with such ungainly long legs and relatively slow movement (see below).

Adults of the phytoseioides species group sensu Lindquist (1964) in the genus Lasioseius are similar to those of Aceodromus and Opilioseius in the hypotrichous condition of the dorsal shield, which lacks podonotal setae z1, z3, z6, s3, r2, r4 and opisthonotal setae J1, J3, S1. They are especially similar to Aceodromus in lacking the true vertical setae, j1, and also s1, s2. However, these similarities are thought to be convergences, with the phytoseioides group being derived from a lineage in Lasioseius which is characterised in part by having heavily sclerotized dorsal and ventral shields, the female ventrianal shield expansive and bearing six pairs of opisthogastric setae, and the female movable chela tridentate.

Adults of the family Podocinidae resemble those of Opilioseius in having long legs, and especially legs II to IV having elongated tarsi that may be three to five times as long as each of the respective tibiae and genua. Legs I of podocinids, however, are disproportionately long relative to legs II to IV, lack claws, and have one or two greatly elongated tactile setae apically, such that their function appears to be strictly tactile, antenna-like, rather than optionally ambulatory. And, while elongation of tarsus I in Opilioseius occurs along its entire length ( Fig. 23 ), that in podocinids differs by the elongation being restricted primarily to the region proximal to the sensory receptor complex, i.e., the region that bears only attenuated solid-core setae (delimited by the angled line in Fig. 30 ). Also, in contrast to tarsus I of Opilioseius having a complete complement of setae typical of the Dermanyssina (6-28/9-6), that of podocinids is setal-deficient in both regions, having a larval complement of setae (along with one protonymphal seta added) in the proximal region and a few less ventral setae in the sensory receptor complex region. Legs II to IV of podocinids have short pretarsi relative to those of Opilioseius . Also, unlike Opilioseius and other blattisociids, podocinids have a three-tined palptarsal apotele, a serrated transverse ridge across the dorsal face of the gnathotectum, a more reduced dorsal body setation that lacks clunal setae J5 and all R - marginal setae, and their males have a holoventral shield. In contrast, legs I of Opilioseius are similar in elongated length to legs IV, lack greatly elongated setae apically, are equipped with small paired claws on long pretarsi like legs II to IV, and are thought to be ambulatory as well as tactile.

Figures

FIGURES 1 – 11. Opilioseius grallator n. sp., adult female: 1, subcapitulum; 2 a – 2 b, corniculi; 3, two views of corniculus and salivary stylet, dorsal view; 4, paralabral processes; 5, tritosternum, showing denticulate chevron at base of laciniae; 6, palpus, dorsolateral view; 7, detail of seta al of palpfemur; 8, chelicera, lateral antiaxial view; 9 a, separate ventrolateral view of movable digit; 9 b, separate paraxial lateral view of movable digit; 10, separate paraxial view of fixed digit; 11, gnathotectum.

FIGURES 12 – 13. Opilioseius grallator n. sp., adult female: 12, idiosoma, dorsal aspect with detail of peritrematal shield; 13, enlarged separate views of dorsal setae denoted.

FIGURES 14 – 16. Opilioseius grallator n. sp., adult female: 14 a – b, detail of spermatheca showing minor duct arising from embolus at base of calyx; 15, detail of peritrematal shield, free from exopodal strip alongside legs II – IV except where they join at mid-level of leg IV; 16, idiosoma, ventral aspect with detail of glandular pores on coxa I.

FIGURES 17 – 22. Opilioseius grallator n. sp., adult female: 17 – 20, legs I-IV, excluding tarsi: 17, leg I, dorsal view; 18, leg II, posterolateral view; 19, leg III, posterolateral view; 20, leg IV, posterolateral view with detail of elongate setae on genu and tibia; 21, tarsus IV, dorsal view; 22 a – b, details of distal structures of tarsus IV: 22 a, ventroapical tarsal process below base of pretarsus, and distal minute tarsal setae ad - 1, pd - 1; 22 b, pretarsal claws, paradactyli and pulvillus.

FIGURES 23 – 31. 23 – 29, Opilioseius grallator n. sp., adult: 23, tarsus I, right leg, dorsal view; 24, tarsus I, detail of tarsal seta “ S ” and associated setae; 25 – 29, male: 25, chelicera, paraxial view; 26 a separate, lateroventral view of movable digit; 26 b, separate, lateroventral view of movable digit with scale over dentate region; 27 a spermatodactyl with ventral scale; 27 b, ventral cheliceral scale; 28, gnathotectum; 29, subcapitulum. 30 – 31, Podocinum sp., adult: 30, tarsus I, right leg, dorsal view; 31, tarsus I, detail of tarsal seta “ S ” and associated setae.

FIGURES 32 – 33. Opilioseius grallator n. sp., adult male: 32, idiosoma, dorsal aspect, with laterally expanded detail of peritrematal shield fused to podonotal dorsal region; 33, idiosoma, ventral view.

FIGURES 34 – 38. 34 – 35, Opilioseius grallator n. sp., deutonymph: 34, idiosoma, dorsal aspect; 35, idiosoma, ventral aspect. 36 – 38, leg III, tarsal apex and pretarsus, showing different forms of ventroapical tarsal processes and conjectured acrotarsal demarcation: 36, Adenoseius sp. (Sejidae), anterolateral view; 37, Euzercon sp. (Euzerconidae), ventral view; 38, Arctacarus rostratus Evans (Arctacaridae), ventral view. Abbreviation: acr mar, acrotarsal margin.

FIGURES 39 – 40. Opilioseius grallator n. sp.: 39, photomicrograph of adult female, dorsoventral habitus view; 40, photomicrograph of gravid adult female, showing relative size of fully developed egg and maternal idiosoma, dorsoventral habitus view.