Neoafrotydeus, André K, 2025

Number of genera in Tydeidae View in CoL View at ENA

The practical agreement which exists between specialists as to the delimitation of genera varies from one zoological group to another. In many groups, this agreement between specialists is poor, and this results in a great instability of the generic classification ( Dubois, 1988: 16).

Figure 2 View Figure 2 gives a histogram based on the monographs, books and catalog listed previously and two cumulative genus description curves since 1831. The first curve provides the number of all new genera and subgenera erected during each decade while the second takes into account synonymies and restoration. The maximum number of genera and subgenera described in Tydeidae is 43 (a total of 45 names – 2 replacement names). After synonymization and restoration, the current number of genera and subgenera in Tydeidae is 30 ( Fig. 2 View Figure 2 ). The instability evoked by Dubois (1988) is discernable through the gap between the two curves.

Depending on the curve selected, the number of genera at the beginning of the 2011-2021 decade amounts to 29-43 and is close to the estimation by Zhang et al. (2011: 130), 30 genera. Both curves apparently begin to flatten during the last 40 years.

Number of species in Tydeidae

A common approach to estimating the total number of extant species in a taxonomic group is to extrapolate from the temporal pattern of known species descriptions ( Bebber et al. 2007). This perspective is not new in mites and was used by Wharton (1964) for mites and Trombiculidae and by André and N’Dri (2013) for mites and Tydeoidea . Yet, such an approach is not recommended due to the data weakness: only 433 tydeid species have been described, figure 3

shows the beginning of a logistic curve and there is no long-term trend sensu Edie et al. (2017).

Nevertheless, a turning point is apparent from figure 3 and is indicated by a double arrow.

Both cumulative curves suggest a change in the description rate manifest trough the slopes estimated before and after the 1951-1960 decade. This is confirmed by the decade trend in species description with a maximum number of 83 species described in a single decade. The turning point coincides with the description of Lorryia formosa by Cooreman (1958) and seems to reflect the influence of agronomic practices.

However, another approach with a new “Pie of Life” was proposed by Larsen et al. (2017) and was based, concerning mites, on Walter and Proctor (2013). The number of described Acari species (including Acariformes and Parasitiformes) is approximately 55,000 (Krantz,

2009: 1). In such a context, 433 described tydeid morphospecies represent less than 1 percent of described Acari (0.79%). If assumptions of Larsen et al. (2017: 248 ; appendix 2 on animal richness, 10.2 million mite species including morpho- and cryptic species) are accepted, this yields 80,301 tydeid species. In the end, if a ratio of 5.9 cryptic species per morphologically based arthropod species is recognized ( Larsen et al. 2017 ; appendix 1), this yields 11,638 tydeid morphospecies. 433 described tydeid morphospecies would then represent only 3.72%

of estimated tydeid morphospecies in the world, less than the 10% recalled by Lindquist (2001: 55) for the eriophyoid fauna.

Obviously, there is no problem of species inflation as in mammals ( Zachos et al., 2013). Only 414 tydeid species had been described for the 2001-2010 decade vs 340 estimated by

Zhang et al. (2011). Τhe temporal pattern of known species descriptions was not modified by synonymies (4 cases) and restoration (2 cases).

Number of names in Tydeidae

Many binomina were given to a specific mite: 2.05 ± 0.76 for all tydeid species. A record is detained by the genus Brachytydeus . For instance, zaheri has five objective synonyms plus a replacement name (not counted): Paralorryia (original combination), Brachytydeus , Kuznetsovia , Lorryia , Tydeus and Venilia .

The number of binomina assigned to early described species is close to one ( Figure 4 View Figure 4 ). For instance, only a single combination has been used for velox Koch described in 1836: Tydeus velox . The same applies for recently described species, i.e. for Brachytydeus altaicus described by Khaustov and Khaustov in 2023, although there hasn’t been enough time to propose objective synonyms to B. altaicus . There are large variations in between. A maximum value (3.5) is reached for species described in the 1881-1890 decade. For instance, there are 5 combinations for granulosus described by Canestrini (1886b): successively Tydeus , Tydulosus , Venilia , Lorryia and Brachytydeus . The trends observed in recent decades seems to indicate a decrease of subsequent combinations. The 17 species directly assigned to Brachytydeus were all described after 2008.

Toward a new concept of Tydeidae

In the Thorian sense, Tydeidae was “difficult to characterize” ( Baker,1965: 96). In the modern sense, a key character advanced by André and Fain (2000) is the recurved prodorsum. This character is shared with Triophtydeidae but is very practical to recognize “real” Tydeidae in the old illustrations of Berlese and even in drawings of Baker (1965). The importance of the ecdysial cleavage line in Acariformes was discussed by Norton and Kethley (1994).

A second key character advanced by André and Fain (2000) is the presence of only two eye-spots vs three in Triophtydeidae . Those spots are silver granules not associated with a lens such as that found in Ereynetidae . As stressed by those authors, the presence of two eye-spots is not ambiguous. In contrast, their absence may refer to a nonobservance, i.e. the failure to observe them (e.g. the spots disappeared) or to a real absence (see Kaźmierski, 1989: 302 ;

André and Fain, 2000: 416). The problem directly concerns Australotydaeus kirstenae in which no eye-spots have been reported and is still more puzzling when a population of Tydeus harbors

3 eyes as observed by André (1985b: 192) and recalled by André and Fain (2000: 412).

As noticed by André and Fain (2000: 437), the family Tydeidae is also characterized by the loss of eugenitals in females and a reduction of the cis-acetabular area. In the calyptostatic tritonymph drawn by Kuznetsov (1980: 1020, his fig. B), the 2 genital openings usually observed in tritonymphs are absent. This reduction is accompanied by the decrease of the chaetome, usually 6 genital setae on both sides of imagines. A decrease of genitals is observed in Acanthodides, Apolorryia , Eotydeus, Momenia , Neolorryia , Pertydeus and Quadrotydeus .

step); H – Apotele setiform ( De Vis et al. 2024); I – Apotele absent ( Knop & Hoy, 1983). Homologous structures have the same pattern. Birefringent structures are outlined (in red in electronic format). Most steps correspond to a species and an article indicated between brackets. A–E: legs I to IV; F–I: leg I only.

The absence of genitals was even observed in the calyptostasic tritonymph of Brachytydeus (Kuznetov, 1980) . Similarly, there are 3 aggenitals (instead of 4) in Apolorryia and Eotydeus.

Such a reduction of genitals may be unilateral (occurring on one side of the body) as noticed by Momen and El-Baghouri (1994), Momen and Solhøy (1996), Momen and Lundquist (1996) and Kaźmierski (1989). The generic significance of this character was questioned by Kaźmierski (1989: 300-301) and the trait will be used to delineate subgenera only. Furthermore, the unilateral presence of 7 genitals reported by Momen and El-Baghouri (1994) and Momen and Solhoy (1996) demonstrates that two forces are governing the evolution of Tydeidae .

On the one hand, the fluctuating asymmetry seems to be caused by random developmental accidents (RDA in Figure 6 View Figure 6 ) not corrected by homeostatic mechanisms normally resulting in a perfect bilateral symmetry ( Leponce et al., 2001). On the other hand, Grandjean (1942) gave an evolutive significance to the unilateral changes he called vertitions (V in Figure 6 View Figure 6 ) and governed by homeostatic mechanisms.

A last distinguishing trait, not evoked by André and Fain (2000), is the presence of at most

8 setae on tarsus I in all Tydeinae and Pretydeinae. Australotydaeinae has a special chaetotaxy with 10 setae on tarsus I and exhibits intermediate characters with other Tydeoidea . This counting is based on the designation system developed by André (1981b).

Other formulae are variable. The most frequent epimeral formula is (3-1-4-2). (3-1-4-3) has been observed in Krantzlorryia , Pretydeus and Tyndareus .

Evolutionary plasticity of Tydeidae

An evolutionary trait-based approach was selected by André (2023) to define the genus Lorryia . In this approach, Tydeidae anticipate the evolutionary traits found in other families of Tydeoidea .

For instance, the reduction of chaetotaxy of tarsus I and the dactyly observed in Tydeidae may be conceived as a vast evolutionary move leading to the fusion or loss of apotele I and the resulting palpian evolution of leg I observed in Iolinidae ( Figure 5 View Figure 5 ).

Another aspect of evolutionary plasticity of Tydeidae is shown by the reduction of the cis-acetabular area and the decrease of the chaetome which also anticipate the evolution of

Iolinidae .

A further facet of evolutionary plasticity of Tydeidae is shown by the partly recessed solenidion, φI, observed in Pretydeus . It does not differ from the ereynetal organ of some ereynetid larva.

A last aspect of evolutionary plasticity of Tydeidae concerns the ontogeny. Apart from a calyptostatic prelarva, described and drawn by Kuznetsov (1980: 1020, his fig. A) and photographed by André and N’Dri (2013: 60, their fig. 50), the ontogeny of Tydeidae includes one six-legged larva (larviparity, drawn by Thor 1933: 52, his fig. 62) followed by four eight-legged stases: the protonymph, deutonymph, tritonymph and imago ( ♀ and ♂). In other words, adulthood (sexual maturity) is observed in imagines only. Based on laboratory colonies

(Brickill, 1958; Kuznetsov, 1980; Liguori et al. 2002 ; Hernandes et al., 2006 ; Silva et al., 2014),

there is no missing stase as in spider mites ( André and Van Impe, 2012) but the tritonymph can be reduced to a calyptostasis as presented and illustrated by Kuznetsov (1980: 1020, his fig. B).

This recalls the intervening calyptostases observed in ereynetid Speleognatinae ( Fain, 1972 ;

André and Fain, 1991).

Nomenclatural acts

Nomenclatural acts (1) to (8) concern families, genera and subgenera, subsequent acts concern species.

(2) Afrotydeus

and its type species, Tydeus munsteri , exhibits the same phanerotaxy as the nominal subgenus Tydeus . Afrotydeus, be it a subgenus or a genus, is thus considered a junior synonym of Tydeus . Topotypes or types of both type species were examined. Consequently, the original combination, namely Tydeus munsteri , has to be used again and any other combination must be set aside. Tydeus (A.) meyerae was moved to Perafrotydeus by André (1980: 142), the other species are placed in a new genus defined hereafter (act 4).

(3) Similarly, the type species of the genus Paralorryia , cumbrensis , has the same organotaxy (leg and idiosoma) as croceus , the type species of Calotydeus . Types of both species were examined. As a result, Paralorryia is thus considered a junior synonym of Calotydeus .

( 4) Neoafrotydeus new genus Zoobank: 1EC6999B-930C-40AB-9AB7-4BF259A477CC

Neoafrotydeus new genus is erected with kenyensis as type species to accommodate Tydeus ( Afrotydeus) flabellifer , T. ( A.) kenyensis , A. novaezealandiae , A. smileyi and A. zairensis , species currently assigned to Afrotydeus, genus synonymized with Tydeus as noted above.

(5) Neohomeotydeus new genus Zoobank: CAAAE9E6-4DB5-441C-92CC-51B15227DB96

Homeotydeus was erected by André (1980) but is not in conformity with ICZN. The 3 species described by Baker (namely arthurbakeri, cumbrensis , shawi) have a seta on trochanter I and were transferred to Calotydeus by André (2005: 995, ambiguous remarks.). The other two species, namely H. bipilis and H. formosus , have a nude trochanter I and are accommodated in a new genus, Neohomeotydeus with H. formosus as type species.

(6) Pertydeus

was described as a subgenus of Tydeus and exhibits the same leg chaetotaxy as the nominal genus Tydeus . The number of genitals is however 5 (vs 6 in Tydeus ). Pertydeus thus re-established in its pristine state and restored as a subgenus of Tydeus ( rest. comb.).

(7) Similarly, Quadrotydeus

is considered to be a subgenus of Brachytydeus characterized by the same leg phanerotaxy but with only 4 genitals ( new comb.).

(8) Similarly, Eotydeus

is considered to be a subgenus of Brachytydeus characterized by the same leg phanerotaxy but with only 2 genitals as in the original description ( new comb.).

(9) Tydeus nieu(w)kerkeni . André (2005) was naming the species after Dr Erik J. van Nieukerken, yet the name was published as nieuwkerkeni, an incorrect original spelling. Under art. 32.5 of ICZN, the correct spelling is emended to nieukerkeni . A “justified emendation” (Art. 33.2.2), if corrected under article 32.5, results in the same author and date as the original name.

(10) Homeotydeus formosa ,

the binomen used by André (1984), does not respect the gender agreement. The original combination corrected under art. 34.2 of ICZN is Homeotydeus formosus which is the type species of the genus Neohomeotydeus .

Table 1 View Table 1 shows that some genera are very close and that the difference may concern only a single seta: Brachytydeus – Kuznetsovtydides (seta on trochanter I), Calotydeus – Tydeus (seta on femur II). Table 1 View Table 1 also masks the within diversity of genera. For instance, chaetotaxy of leg II in Idiolorryia is displayed (6-2-1-3-0) while it has been observed a single seta on tibia. Variations in leg chaetotaxy was explored by Momen and Lundqvist (1993). Similarly, there are 4 or 5 genitals in Neolorryia , 2 to 4 in Eotydeus. Consequently, the division into subgenera is debatable due to the high variability of the number of genitals. Edlorryia based on a deutonymph, Lasiotydaeus and Melanotydaeus ( genus inquirendus) do not figure in table 1.