We herein recognize 26 valid species names in the genus Ololaelaps, and at least four synonyms (Table 1). The majority of species need redescription, including four species that are nearly entirely unknown morphologically (O. hemisphaera, holaspis, platensis, sinensis). While some species are relatively well understood (e.g., O. formidabilis, placentula, sellnicki, ussuriensis, wangi), they nevertheless require additional study to elucidate intraspecific variability, in turn to better distinguish them from close relatives (Table 2). Table 2 presents some of the available diagnostic features of species, which are few. Indeed, identification of most species is problematic; our attempt to prepare a useful key to species was unsuccessful, due to the limited set of reliable diagnostic characters for most species. Other characters not presented in Table 2 may become useful (see Discussion), but intraspecific variability and their diagnostic potential remain to be determined. The case of O. mooiensis, a senior synonym of O. gamagarensis as established by Nemati et al. (2018), is a good example of intraspecific variation of characters, including the degree of fusion of the metapodal platelet – free to completely fused – with the hologastric shield, and the length of sternal setae. These two characters were apparent differences between O. mooiensis and O. gamararensis (Jordaan and Loots 1987) but now appear as mere variation along a range within a single species (A Nemati pers. comm.). Other names in Table 2 may represent synonyms.

The identity of Iphis haemisphaericus (Koch 1839b) is complicated. The species is placed by some authors in Ololaelaps (Laelapidae) and in Stylochirus (Ologamasidae) by others (Table 3). Berlese (1914) redescribed the species as Gamasiphis (Periphis) haemisphaericus (Koch) based on non-type specimens that he collected from Italy. Following Berlese’s concept, Sellnick (1958) and Vitzthum (1943) mention Periphis haemisphaericus (Koch), and Lee (1970) redescribed the species as Stylochirus (= Periphis) haemisphaericus using female specimens from Italy that Berlese (1914) himself had studied for his description. Stylochirus haemisphaericus (Koch) is listed in the catalogue of Ologamasidae by Castilho et al. (2016).

Meanwhile, Sellnick (1940) redescribed the species as Ololaelaps haemisphaericus (Koch). His interpretation of haemisphaericus as an Ololaelaps species has been followed by some authors (Haarlov 1943, Franz and Beir 1948, Willmann 1949, 1950, 1952, Piryanik 1962, Reitblat 1963) until Bregetova and Koroleva (1964) proposed O. sellnicki as a nom. nov. for O. haemisphaericus (Koch 1839b). Bregetova and Koroleva (1964) argued that using a new name was better than using the confusing name haemisphaericus, which was also applied to other species in at least one other family. Before Sellnick (1940), Oudemans (1906, 1929, 1936) mentioned Iphis haemisphaericus as conspecific either with O. placentula or with O. venetus. Oudemans (1936: 217) stated that Berlese erroneously identified a different species as “Periphis haemisphaericus” (certainly referring to Berlese 1914).

There is no indication that anyone examined Koch’s types of haemisphaericus, and the types of most species described by Koch are presumably lost. Therefore, it may be impossible to confirm with certainty whether Koch’s species is Stylochirus or Ololaelaps. Resolving this dual identity of Iphis haemisphaericus (Koch 1839b) will require submitting a case to the International Commission of Zoological Nomenclature. Because the name Ololaelaps sellnicki Bregetova and Koroleva is frequently used, and the name haemisphaericus Koch has been more recently applied in the sense of an ologamasid and not as an Ololaelaps species, the best approach may be to designate (1) a neotype for Stylochirus haemisphaericus (Koch 1839b) and (2) a lectotype for Ololaelaps sellnicki Bregetova and Koroleva (1964) in order to maintain the prevailing concepts of these names. Note that Bregetova and Koroleva (1964) had not designated a type for O. sellnicki since they treated sellnicki as a replacement name for haemisphaericus, but the specimens they studied can be considered as syntypes.

Hennessey and Farrier (1988) synonymized O. venetus (Berlese 1903), a Palearctic species (and the type species of the genus), with O. placidus (Banks 1895), a species otherwise previously restricted to the Nearctic region. However, despite Hennessey and Farrier’s (1988) analysis, we refrain from accepting this synonymy because we consider that these two species (or populations) from North America and Eurasia are not known in sufficient details yet (see further explanations in the Discussion). Nonetheless, we accept for now the synonymy of O. venetus and O. halaskovae (the latter is also Palearctic), which was originally proposed by Evans and Till (1966) and also accepted by Bregetova (1977a). However, Evans and Till (1966) did not specify what specimens they used for their redescriptions of O. venetus and O. placentula and whether they examined Berlese’s types.

Some species names once considered as Ololaelaps are herein excluded from the genus, based on the interpretation of the original description or more recent publications (Table 3): the two ologamasids Hydrogamasus coleoptratus and Sessiluncus holostaspoides, the laelapid Pseudoparasitus germanicus, and the nomen dubium Ololaelaps (Cypholaelaps) haemisphaericus Berlese (not Koch). The type of the latter should be re-examined. From our current understanding, other species with doubtful identity cannot be excluded from Ololaelaps with certainty: Zercon festivus, Iphis globulus and Eumaeus inornatus (Table 3). Unfortunately, the types of those species may be lost. Note that Ololaelaps is distinct from ‘Oolaelaps’ which usually refers to species now placed in Holostaspis (Laelapidae) (Keum et al. 2017).

Although Evans and Till (1966) treated the genus Ololaelaps as feminine (indicated by O. venetus), Berlese (1904) originally treated it as masculine, indicated by two species that he originally included in the genus which had names in adjectival forms with clear masculine ending: O. venetus and O. coleoptratus. We herein follow Berlese and treat Ololaelaps as masculine for the following reason. As per Article 30.1.1 of the ICZN, “a genus-group name that is or ends in a Latin word takes the gender given for that word in standard Latin dictionaries”. The name Ololaelaps, as created by Berlese, probably stands for ‘holo’, ancient Greek for ‘complete’, putatively referring to the nearly completely sclerotized idiosoma, or opisthogaster, of the mites he included in the genus at the time; and ‘laelaps’, borrowed from the generic name Laelaps, first used by Koch (1836). Like Berlese (e.g., Laelaps spiniferus Berl., L. myrmecophilus Berl.), Koch appears to have treated Laelaps as masculine (as in L. festinus Koch 1839a). In Latin dictionaries (e.g., Lewis and Short 1879), Laelaps is masculine and refers to the Greek mythological dog of that name. Koch’s choice itself was almost certainly for that mythological hound which was known to never fail to catch its prey. ‘Laelaps’ was originally borrowed from Greek and means ‘hurricane’. Treating Ololaelaps as masculine results in the change of a single species name from its original ending: O. obovata to O. obovatus. Note that some species names are feminine, such as placentula (= little cake) and hemisphaera (= hemisphere), but these are nouns in apposition and have therefore invariable spellings, irrespective of the gender of the genus.

At present, Ololaelaps appears as a relatively well-defined genus, characterized by a unique combination of characters, many of which, individually, are shared with other genera of Laelapidae, especially hypoaspidines. The most unique feature of Ololaelaps is the female genital shield hyperdeveloped posteriorly and fused with the anal shield to occupy most of the opisthogaster and capture 3–5 pairs of setae in addition to st5 and circumanals. The genital shield is also expanded in several other genera (e.g., Laelaspis, Laelaspisella, Pseudoparasitus, Pogonolaelaps; Evans and Till 1966, Hunter 1966, Joharchi et al. 2016, Nemati and Gwiazdowicz 2016) but it is never fused to the anal shield like in Ololaelaps, except in Oloopticus (Karg 1978). Oloopticus is distinguished from Ololaelaps at least by the sternal shield coalesced anteriorly with presternal platelets and posteriorly with endopodal plates, and by the modification of setae st4 into sensory ‘pits’. Karg and Schorlemmer (2013) suggested that Ololaelaps and Oloopticus are closely related genera, based on the hypothesis that they apomorphically share a hologastric (genitiventrianal) shield (Karg 2000). However, this character state could have evolved independently in these two genera, which otherwise appear phylogenetically distant. The fusion of epigynal + ventral + anal shields also occurs in members of Eviphidoidea, such as Holaspulus, some Holaspina (Parholaspididae; Halliday 1995, Nawar and El-Sherif 1995) and Indutolaelaps (a genus similar to Holaspina; Leptolaelapidae; Karg 1997).

The hemispherical nature of the idiosoma of several species of Ololaelaps is also distinctive. However, this attribute may have led to misidentifications or misclassifications in the past, as some species in other families, especially Ologamasidae, have a similarly glossy, dome-shaped dorsal shield (see Table 3). That would explain in part the apparent dual identity of Iphis haemisphaericus, associated with two phylogenetically distinct genera, Stylochirus (Ologamasidae) and Ololaelaps (see Remarks for the genus above). Unfortunately, Koch (1839b) illustrated only the dorsal aspect of that mite. Another similarity is that ologamasids also tend to be strongly sclerotized ventrally, and that may have added to the confusion. Old species names of uncertain identity (Table 3: Zercon festivus, Iphis globulus, Eumaeus inornatus) may have been historically associated with (valid) Ololaelaps species for similar reasons. Some Eviphididae also have subglobular, domed idiosomas (Mašán and Halliday 2010).

As explained in Kazemi and Beaulieu (2016), the recently described monotypic genus Persicolaelaps shares many features with Ololaelaps, notably the dome-like dorsal shield bearing attenuate setae, and well-developed exopodal strips that are fused anteriorly with the sternal shield’s anterolateral arms (via endopodal elements). Note that such (anterior) fusion of exopodal-sternal shields occurs in other laelapids (e.g., Alloparasitus oblongus (Halbert); Evans and Till 1966). A pair of sclerotized presternal platelets, a three-tined palp-apotele, and well-developed parapodal plates characterize Ololaelaps as well as species of other hypoaspidine genera, especially of Pseudoparasitus and Gymnolaelaps (Hunter 1966, Joharchi et al. 2011, Nemati and Gwiazdowicz 2016). In addition to both having a reduced third (proximal) tine in their palp apotele (in contrast to a well-developed proximal tine in at least some Gymnolaelaps), Pseudoparasitus and Ololaelaps are also similar in having setae JV1 and JV2 inserted on the genital shield, but remotely from the lateral margins (vs on or near the shield margins in Gymnolaelaps or Laelaspis) (Joharchi et al. 2011). A three-tined palp-apotele was used as one of the main characters defining previous concepts of the family Neoparasitidae (Vitzthum 1943, Evans 1957, Mašán and Halliday 2014: 51) which was composed of various genera now scattered in at least four relatively distant families of Gamasina.

An additional set of features that further distinguish some Ololaelaps species from other laelapid genera is the various fusions of the peritrematal, parapodal, metapodal and hologastric shields. Even for groups with opisthogastric (i.e., genitiventral) shields such as Laelaspis and Pseudoparasitus, we are not aware of such fusion among shields. The peritrematal and parapodal shields, however, are coalesced in a few other laelapids, such as Nidilaelaps annectans (Womersley) (Shaw 2012).

The female of some Ololaelaps species have seta st4 and poroid iv3 on the sternal shield. This is rare in laelapids, although common within other groups, especially Rhodacaroidea. Seta st4 is also born on the sternal shield (complex) in groups where the shield is fused posteriorly with endopodals (e.g., many ologamasids and pachylaelapids). However, in Ololaelaps, this feature seems associated with the anterolateral expansion of the genital shield, which leaves little soft cuticle available for the insertion of st4 and iv3. In other genera where the genital shield is more pronounced anteriorly, st4 has even disappeared (Kazemi and Beaulieu 2016). This ‘weaker’ seta, formed only during the deutonymphal stage, is also repressed in the adults or even the deutonymphs of other gamasines (Evans and Till 1965, Karg 2000, Lindquist 2003, Kazemi and Beaulieu 2016).

The males of Ololaelaps are not as distinctive as females, although they can be distinguished from those of most other laelapid genera by the degree of development of the holoventral shield posterolaterally and its fusion to parapodal-exopodal shields, and sometimes to the peritrematal shields. However, a similar ventral shield arrangement occurs in the males of other laelapids, for instance N. annectans (Shaw 2012) and Pseudoparasitus missouriensis (Ewing) (as P. austriacus (Sellnick), Hunter 1966). The ventrolateral extensions of the dorsal shield is an additional feature facilitating genus diagnosis (occurring in both sexes of Ololaelaps), which is uncommon in Laelapidae, and perhaps otherwise limited to species of Gymnolaelaps (Evans and Till 1966, Joharchi and Halliday 2013). Also, the peritrematal shield is fused to the dorsal shield along most of its length in the male of some species (e.g., O. ussuriensis).

While it may be easy to identify a given Ololaelaps mite to genus, it is more difficult to identify it to species. Examination of types, as well as a critical assessment of intraspecific variation based on additional specimens will be necessary to clarify species boundaries and uncover synonymies. In particular, the following characters should be scrutinized during species (re)descriptions.

The type of fusion between metapodal, peritrematal, parapodal, and hologastric plates appears as a useful starting point to initiate species identification, because it sorts species into broad groups, which are phylogenetically meaningful in some cases (Table 2). Bregetova and Koroleva (1964) implied, in their key, the existence of two species groups, which have been further defined by Evans and Till (1966) based on a limited number of species: the venetus and placentula groups. The venetus group represents a small cluster of similar species (O. venetus, placidus, sellnicki) that nonetheless need further study. It is herein defined by five characters, some of which are likely derived (apomorphic), relative to the ancestor of the genus (Table 2):

(1) Fused peritrematal-hologastric-parapodal shields by way of the metapodal platelet. Note that the parapodal plate ranges from clearly to ambiguously fused to, or merely tightly contiguous with, the metapodal ‘bridge’ (e.g., compare figs 74–76 in Hennessey and Farrier (1988), figs 17, 21 in Bregetova and Koroleva (1964), and figs 49–50 in Evans and Till (1966)). Regarding this character, O. hemisphaera (Berlese 1916b) appears similar to species of the venetus group because its parapodal plate, albeit free, is (nearly) contiguous with the peritrematal shield (or metapodal bridge) (based on Ryke 1962). The peritrematal shield is also fused to the hologastric shield in O. interruptus and O. leptochelae, but the parapodal plate is clearly free of the fusion. Note that the original illustration of O. venetus by Berlese (1889; as misidentified “Laelaps tumidulus (Koch)”) shows both the peritrematal and parapodal plates free from the hologastric shield, which is discordant with all other descriptions of O. venetus (or syn. O. halaskovae; Table 2). However, the illustration of the male spermatodactyl (Berlese 1889) shows a sinuous groove, like that of O. venetus and related species.

(2) Spermathecal ducts (= tubuli annulati, Evans 1992) well sclerotized, conspicuous, and similarly shaped in O. venetus, O. placidus and O. sellnicki. The spermathecae were also illustrated for O. translineatus (Barilo 1991) and O. mooiensis (including the sacculus foemineus; Marais and Loots 1972, Jordaan and Loots 1987), but they seem distinct from those of the venetus group of species. Hennessey and Farrier (1988) synonymized O. venetus with O. placidus certainly in part based on their similarity in the shape of the spermathecal ducts. They have indeed similar ducts, but the variation that we have observed between females of O. placidus, and between O. placidus and one or more undescribed, closely related species suggests that the shapes of the spermathecal ducts may overlap between species. The distinction between the spermatheca of O. sellnicki vs O. venetus or O. placidus may also not be so straightforward, given that the short subapical appendage characteristic of the ducts of O. venetus and O. placidus is not always discernible, and also that the ducts of all three species can be seen as apically ‘closed’ and rounded, or open-ended (Bregetova and Koroleva 1964; Hennessey and Farrier 1988; FB, pers. obs.).

(3) Spermatodactyl with a sinuous duct, and a subapical hump or bend (Bregetova and Koroleva 1964; Evans and Till 1966; F.B. pers. obs. for O. placidus). In contrast, the males of O. formidabilis, O. placentula, O. translineatus and O. ussuriensis have spermatodactyls of various lengths with a straight duct and no hump subapically; the spermatodactyl of O. rectagoni also has a straight duct and is swollen subapically (Karg 1994).

(4) Dorsal shield with narrow, smooth epipleura (i.e., ventrolateral extensions of the dorsal shield) vs broad, lineate-reticulate epipleura of the placentula group. Other species may have narrow epipleura, smooth or reticulate but descriptions are often lacking in such details, in part because determining the extent of the epipleura is most readily done before slide-mounting of the specimen (Barilo 1991) or on slide-mounted specimens with unbroken dorsal shield.

(5) A fifth character associated with the venetus group is the insertion of setae JV3 and ZV2 off the hologastric shield in O. sellnicki and in some individuals of O. venetus and O. placidus (Table 2; Ryke (1962), Bregetova and Koroleva (1964); FB, pers. obs. for O. placidus). This contrasts with all other known species, described with JV3 and ZV2 on the hologastric shield. Two other deviations from normal are seen in the illustrations of O. obovatus (Womersley 1960) and O. platensis (in Ryke 1962), both lacking ZV1, and of O. rectagoni (Karg 1993b) having ZV3 inserted on the shield.

The placentula group was defined by four characters (three mentioned by Evans and Till (1966), a fourth one only by Bregetova and Koroleva (1964)), none of which are clearly apomorphic, considering their (albeit poorly known) distribution across species in the genus (Table 2):

(1) six other species have the metapodal platelet fused to the hologastric shield (and free from parapodal/peritrematal plates), making this type of fusion relatively common in the genus (Table 2);

(2) a poorly sclerotized (i.e., inconspicuous) spermatheca may characterize other species, given that it has been described in five species only (see above);

(3) at least two other species have the spermatodactyl with a non-sinuous duct (see above); and

(4) several other species have reticulate or lineate-reticulate epipleura that at least superficially resemble those of the placentula group of species. The ventral extent of the epipleura and its exact type of ornamentation should be scrutinized for each species. Members of the placentula group, O. placentula, O. ussuriensis and presumably O. caucasicus (note that O. ussuriensis and O. caucasicus were not illustrated dorsally) have a dorsal shield smooth or faintly reticulate, in contrast to conspicuously lineate-reticulate epipleura, which are relatively well extended ventrally (Table 2); this lineation-reticulation of the epipleura extends also anterodorsally to the region of setae j1–j2 and z1–z2. Ololaelaps dililoensis appears to have all diagnostic characters of the placentula group, but also has a clearly reticulate dorsal shield, at least in its posterior half. In O. formidabilis, the dorsal shield is only narrowly extending ventrally, but that region is conspicuously reticulated, in contrast (similarly to the placentula group) to the light, inconspicuous reticulation of the dorsal region of the shield.

Ololaelaps burdwanensis, O. translineatus, and O. wangi represent a cluster of very similar species. Finally, the last grouping in Table 2 (O. bregetovae and following species) may also represent a natural group, but given the intraspecific variation observed elsewhere (in O. mooiensis, see below; Table 2), it seems yet inappropriate to define a group based on the absence of fusion of shields (metapodal etc.) alone, especially given that all of these species need redescription.

The degree of fusion of the metapodal platelet with the various surrounding shields may vary significantly intraspecifically, as seen in O. mooiensis (incl. syn. O. gamagarensis; Nemati et al. 2018) where the metapodal platelet is exceptionally free from the hologastric shield in some individuals (Table 2). Some variation in the degree of fusion of the metapodal platelet with the hologastric shield also occurs in other species, such as O. placentula (Ryke 1962, Bregetova and Koroleva 1964, Evans and Till 1966); we have also observed, exceptionally, a specimen of that species with a metapodal platelet narrowly fused to the parapodal plate! Other examples are (1) O. formidabilis, having its metapodal platelet contiguous with, to indistinctly fused to, the hologastric shield (Fig. 3A, C–E), and (2) species in the venetus group, where the parapodal plate is clearly to ambiguously fused with the bridge (= metapodal) between the peritrematal and hologastric shields. Barilo (1991) also mentions that the ‘exopodal shields’ (= exopodal-parapodal) could be free or partly connected with the genitiventrianal shield in O. translineatus. Such intraspecific variation in shield fusion calls for caution when identifying species or sorting species into groups (as those presented in Table 2).

Intraspecific variation in shield fusions may occur in males too. For instance, some males that we identified as O. placidus have the peritrematal shield fused to the hologastric shield, just like the male of O. venetus, and others have the peritrematal shield free posteriorly, like that of the male of O. sellnicki (Bregetova 1977a).

At present, the chaetotaxy and the ornamentation of the dorsal shield are not clearly described for most Ololaelaps species (Table 2). At least some species (O. formidabilis; O. placentula, Evans and Till (1966); O. mooiensis, Marais and Loots (1972)) have a complete (or normal) dorsal chaetotaxy for a Laelapidae (sensu Evans and Till 1965). The illustrations of several other species indicate a slightly reduced dorsal chaetome. However, this should be verified, especially for setae apparently missing from marginal areas, in the r and S series, because these setae are difficult to discern in Ololaelaps species, which typically have slender setae and dark, heavily sclerotized dorsal shields. The presence of a single unpaired seta Jx is common in the genus; at least ten described species have it, four of which (O. formidabilis, caucasicus, mooiensis, placidus) have Jx present in some individuals, but absent in others. We suspect that this pliable character also varies in other species and that a Jx seta is expressed in some individuals only. The ornamentation of the dorsal shield is difficult to discern for species with light reticulation (e.g., O. formidabilis). Clearing the specimens thoroughly or slide-mounting some specimens dorsal side up should help; crushing selected specimens on the slide or dissecting their dorsal shield from the ventral idiosoma are other options.

Presently, differences in dimensions of the dorsal, sternal, and hologastric shields are only useful to separate species with marked differences, i.e., with elongate (e.g., O. tasmanicus) vs broad shields (e.g., O. placentula), because intraspecific variation is not sufficiently known. Ratios of length/width could be particularly useful, but they also vary intraspecifically, e.g., the sternal shield of O. venetus appears to have a length/width ratio of 0.8–1.0 (Bregetova and Koroleva 1964, Evans and Till 1966).

The position of seta st4 and poroid iv3 is difficult to use as a diagnostic character because it is not easy to determine whether they are on the shield margin, on the adjacent soft cuticle, or on the endopodal plate. This body region being the point of meeting of three shields (sternal, endopodal, hologastric) renders its study more difficult, obscuring the position of st4 and iv3, especially if they are inserted on soft cuticle, which can be folded above or underneath shields’ margins. Examining several specimens for each species can help, as well as making observations at different focal depths. We suspect that in most cases where st4 (and iv3) appears on the endopodal plate (e.g., O. burdwanensis, O. sitalaensis, O. translineatus), it is actually inserted on soft cuticle that overlaps the plate. Note that the position of st4 and iv3 are relatively stable within genera or even families of Gamasina, whether on soft cuticle, on metasternal platelets or (more rarely) on the sternal shield (e.g., Kazemi et al. 2008, Lindquist et al. 2009, Moraza and Linquist 2011).

The ornamentation of the hologastric shield shows species-specific patterns, such as inverted V or U-shaped ridges in O. formidabilis and undescribed species, as well as the shape of cells in the reticulation pattern (e.g., Barilo 1991). However, inter- and intraspecific variability needs to be ascertained, including for O. placidus, O. venetus and O. sellnicki. Bregetova and Koroleva (1964) and Bregetova (1977a) distinguished O. sellnicki from its close relative O. venetus, as well as O. caucasicus from O. ussuriensis, based on the hologastric shield having cells elongate transversally (O. sellnicki, O. caucasicus) vs regular cells or scales (O. venetus, O. ussuriensis). However, Evans and Till (1966) did not mention such distinction between O. sellnicki and O. venetus, perhaps because the distinction is not so straightforward. The cells of the reticulation also vary in shape, size, and conspicuousness (i.e., in the strength of the ridges) across the longitudinal (anterior to posterior) axis, and this ‘gradient’ may differ between species (Bregetova and Koroleva 1964). There is also interspecific differences in patterns of ridges on the sternal shields (Barilo 1991, Table 2; unpubl. data on undescribed species).

Our knowledge of the gnathosoma of Ololaelaps indicates limited variation between species. For instance, the internal malae have two pairs of projections in the females of all species where the hypostome has been described (O. caucasicus, dililoensis, formidabilis, mooiensis, placentula, placidus, sellnicki, ussuriensis, venetus, wangi) except for O. sitalaensis which lacks the lateral pair, based on the illustration in Bhattacharyya (1978). In contrast, the lateral pair of projections is missing in the males of all species where the hypostome have been described and the median projections are more fimbriate than those of females (O. formidabilis, Fig. 7; O. sellnicki, Bregetova and Koroleva 1964, Evans and Till 1966; O. placidus, unpubl. data). The number of rows of deutosternal denticles apparently varies at least intraspecifically (5–6 in O. formidabilis; 6–7 in O. placidus). On the other hand, there seems to be some interspecific variation in the number of denticles per rows, although often overlapping, with some species having six or fewer denticles per row (e.g., O. formidabilis, ussuriensis, wangi) and others having 5–10 denticles per row (O. caucasicus, placentula) (Bregetova and Koroleva 1964, Evans and Till 1966, Barilo 1991, Keum et al. 2017). Variation in cheliceral dentition is most notable for O. interruptus and O. leptochelae (see Table 2).

Idiosomal adenotaxy differs between laelapid species (Kazemi et al. 2014). Although the adenotaxy of only a few species of Ololaelaps has been studied, we have noticed variation in the position and shape of gland openings gd4 and gd9. This may prove to be useful in distinguishing species, especially as they often are easy to locate, being usually on or near the shield margin (on the ventrolateral extension) (e.g., figs 5, 13 in Bregetova and Koroleva (1964); Hassan 1989). Interestingly, the putatively related genus Pseudoparasitus has at least some members (Pseudoparasitus sp. near centralis Berl.; unpubl. data) with gd4 and gd9 in similar positions, on the shield margin.

While the legs of Ololaelaps species mostly bear simple and slender setae, there is interspecific variation in the shape of setae. This should be investigated and exploited for species diagnostics (see examples in the genus description above).