Lasioseius minor Kalúz, 2009

Mašán, Peter, 2023, On some blattisociid mites (Acari: Mesostigmata: Lasioseius, Cheiroseius) from Slovakia, with notes on the genus Hyattella sensu Krantz, 1962, Zootaxa 5361 (2), pp. 159-180 : 173-176

Notes on Lasioseius minor Kalúz, 2009

Lasioseius minor was described as one of the smallest species native to Europe ( Fig. 29 ), based on females from a soil sample from a thermophilic oak forest in southwestern Slovakia ( Kalúz 2009: 1157). The dorsal shield of this species ( Fig. 34 ) was originally described and illustrated with the correct number of 36 pairs of setae, but as a revision of the type specimens and my own material showed, the idiosomal setation was misinterpreted in some details: (1) the paravertical setae (z1) are shown in the original illustration of the dorsal shield, although they were absent from all four type specimens available for my study; (2) setae s2 (labeled r2) are considered to be located outside the shield, but are clearly part of the number of 36 pairs of dorsal shield setae, as in other species of the genus; (3) setae ZV5 are omitted and absent from the original illustrations of the idiosoma, although they are normally located behind R6. In addition, Kalúz (2009) misinterpreted the chaetotaxy of several leg segments (trochanter II, femur II, and tarsi II‒IV), which are in fact characterised by the standard number of setae, as is the case in most species of the genus.

Christian (1990: 31) described an equally small and similar Lasioseius species, namely L. kargi , from the leaf litter of a deciduous forest in Germany [the holotype was examined via ʻThe Virtual Microslide Collectionʼ of the ʻSenckenberg Museum für Naturkunde Görlitzʼ; see Christian et al. (2018)]. Like L. minor , the species is also characterised by the absence of paravertical setae [this feature is found exclusively in morphologically distinct members of the L. phytoseioides species group, as defined by Moraes et al. (2015b)], the placement of marginal setae r5 on the dorsal shield, the presence of six pairs of pre-anal setae on the ventrianal shield, the relatively large outer pair of metapodal platelets, and the unusual four teeth on the movable digit of the chelicerae.

Just as Kalúz (2009) overlooked the existence of L. kargi Christian, 1990 , Christian (1990) also overlooked the existence of L. kargi Kandil, 1980 . Only later Christian & Karg (2006: 125) assigned a new replacement name for the homonymous species established by Christian (1990), namely L. diffindatus Christian & Karg, 2006 . Based on my comparisons of the type specimens of L. minor and L. diffindatus as well as an examination of my own numerous specimens from Slovakia, I consider both species to be identical. Therefore, I relegate L. minor into synonymy with L. diffindatus .

There is only one minor inconsistency in the morphological concepts of L. minor and L. diffindatus that could be commented on. In contrast to the illustration of the metapodal areas in Kalúz (2009), Christian‘s illustration of these areas lacks the anteromedial pair of platelets, which are indeed very small and suboval and resemble sclerites rather than platelets. According to Christian and his photographs (personal communication), these structures are abnormally and asymmetrically developed in the holotype (the only type specimen available). On the right side, this platelet is divided into two smaller ones, and on the left side, it is not free and well separated, as it usually is, but lies close to the edge of the adjacent larger platelet. In this context, Lindquist (1964) and Moraza & Lindquist (2011) pointed out the variability of metapodal scutal elements in some species of Lasioseius . They gave the following two examples: in L. confusus Evans, 1958 , the metapodals vary from entire to partly subdivided, to entirely subdivided but contiguous, while in L. allii Chant, 1958 they are consistently subdivided, although the smaller platelet may be very small in some specimens.

It is interesting to note that these two identical species proposed here for synonymisation were placed in two different subgenera by their original describers, namely L. minor in Crinidens Karg, 1980 [synonymised by Moraza & Lindquist (2011) under the nominate subgenus] and L. diffindatus in Lasioseius s. str. This difference in placement was mainly a consequence of Christian (1990) describing and illustrating the metapodal areas of this species with only one pair of metapodal platelets instead of two.

The undescribed male stage is unusual by almost complete reduction of R and UR rows of setae (only R3 present and placed on soft cuticle; compared to female, five pairs of R setae and two pairs of UR setae are absent); setae r6 on dorsal shield, not on soft cuticle as in female; ventrianal region with only JV1‒JV3, JV5, ZV1 and ZV2 on ventrianal shield, and ZV5 on soft integument (compared to female, JV4, ZV3, and ZV4 are absent).

This thermophilic and saproxylic species is not rare in Slovakia, and I collected it on the vast territory of southern Slovakia in the following habitats: on wood-destroying fungi on deciduous trees (eight finds), under the bark of deciduous trees (seven finds), in decomposing wood of old oaks inhabited by a colony of ants (five finds), in leaf litter of oak forests (two finds), in nests of Micromammalia and in decaying plant remains (one find each). In Slovakia I have not yet found this species in higher and colder areas in the central and northern regions or in association with conifers.

Figures

FIGURE 34. Lasioseius diffindatus, dorsal idiosoma of female. Scale bar: 50 µm.

FIGURES 27–31. Lasioseius spp., dorsoventral habitus. 27. L. cheiroseioides sp. nov. (female); 28. L. epicrioides (female); 29. L. diffindatus (female); 30. L. lacunosus (male); 31. L. lacunosus (female). Scale bar: 300 µm.