Prozercon Sellnick 1943

Genus Prozercon Sellnick, 1943

Prozercon Sellnick, 1943 in Willmann 1943: 211; Sellnick, 1944: 40; 1958b: 125; 1958a: 362; Halašková, 1963: 145; 1969: 344; 1977: 70; Karg, 1971: 303; 1993: 310; Błaszak, 1974: 65; 1976: 565; 1978: 318; 1979a: 77; Petrova, 1977a: 583; Balan, 1992: 34; Urhan & Ayyildiz, 1992: 84; 1996a: 570; 1996b: 259; Urhan, 1998a: 533; 2008: 103; Mašán & Fenďa, 2004: 62.

Type species: Zercon fimbriatus C. L. Koch, 1839 by original designation.

Prozercon (Plumatozercon) Balan, 1992: 36 (nomen nudum, type species not designated).

Prozercon (Plumatozercon) Urhan & Ayyildiz, 1996c: 796; Urhan, 1998b: 9. syn. nov.

Type species. Prozercon lutulentus Halašková, 1963, by original designation.

Rafas Błaszak, 1979b: 14; Urhan & Ayyildiz, 1996d: 582. syn. nov.

Type species Rafas bisternalis Błaszak, 1979, by original designation.

Diagnosis. Podonotal shield carapace-like, expanded anteroventrally and lateroventrally, setae j1 situated ventrally. Peritrematal shields separated from dorsal shields by a narrow slit of membranous cuticle, their posterolateral tips expanded posteriorly. Peritremes expanded to anterior half of coxae III, straight or slightly bent. Setae r1 and r3 shifted ventrally to peritrematal shields, both short, r3 always smooth and needle-like. Setae z1 absent. Glands gv2 absent. Ventrianal shield bearing 19 setae, setae ZV1 absent. Glands gv3 situated laterally or anterolaterally to adanal setae. Margin of opisthonotum with six or seven pairs of R-setae.

Notes on the genus. Great variety can be observed in the shape of the peritrematal shields and the position of ventral shields in recent Prozercon species. A group of species has freely-ending peritrematal shields in both female and male, and the size of the posterolateral expansion of shields is characteristic for species. However there is precedent for individual variability, even within a population (see P. graecus sp. nov. below). In another group, the peritrematal shields of the female end freely, while they are fused with the ventrianal and dorsal shields in the males (e.g. P. morazae sp. nov.), and in a few species all three shields are fused together in both sexes.

The subgenus Prozercon (Plumatozercon) was established by Balan (1992), including two species, P. lutulentus Halašková, 1963 and P. halaskovae Petrova, 1977b, but Balan failed to designate a type species and the name is therefore not available. The name Plumatozercon was first made available in Urhan & Ayyildiz (1996c), who gave a short diagnosis accompanied by designation of P. lutulentus as type species of the subgenus. Peritrematal seta r1 is always short in Prozercon, but may be either pilose or smooth. This is the only character for distinguishing the subgenera Prozercon and Plumatozercon. The distinguishing character of the subgenera Prozercon and Plumatozercon is clearly unstable (as e.g. shape of r1 varies even within a population of P. graceus sp. nov. from needlelike to pilose), and therefore it does not reflect phylogenetic divergence. Accordingly, I propose that Plumatozercon is a junior synonym of the subgenus Prozercon.

The sternal shield of the female and the sternigenital shield of the male are weakly sclerotised in many Prozercon species, which is often expressed in the presence of a weakly sclerotised band between sternal setae st1 and st2 (Figs 1–4) (e.g. Cälugär, 2004). Rarely it appears that setae st1 are inserted on small, isolated platelets (Moraza, 1988). A similar phenomenon was described by Błaszak (1979b) as the sternal shield of the female and sternigenital shield of the male completely divided behind setae st1, and this served as a major distinguishing feature of the genera Rafas and Prozercon. After reviewing the type specimens of Prozercon bisternalis (Błaszak, 1979b) (deposited in Collection of Soil Zoology, Hungarian Natural History Museum), I have found that P. bisternalis and many Prozercon species (e.g. some specimens of P. graecus sp. nov.) are identical, and there is no evidence that the anterior sternal region of Rafas develops separately as a jugular shield. Moreover, in the holotype and some paratypes of P. bisternalis, the sternal shield seems to be undivided (Fig. 4), therefore it is a character of individual variability as well. Accordingly, this character should not be used in generic delimitation. Another distinctive feature of Rafas was that there are only seven pairs of marginal setae on the opisthonotum, while the Prozercon species bear eight pairs of setae in the same position (Błaszak, 1979b). However this is not true inasmuch as numerous species of Prozercon characteristically possess seven pairs of marginal setae (variation in number of opisthomarginal setae is discussed below). I therefore propose that Rafas is a junior synonym of Prozercon, which results in two new combinations as Prozercon bisternalis (Błaszak, 1979b) comb. nov. and Prozercon blaszaki (Urhan & Ayyildiz, 1996d) comb. nov.

Absence of gland openings gv2 seems to be a stable apomorphy (however it is shared with many other genera) as it lacks in every Prozercon species I have ever observed. It serves as a basis for distinguishing the genera Aleksozercon Petrova, 1978 (where a single opening of gv2 present) and Prozercon, while these genera share all other important characters. The single species Aleksozercon zachvatkini Petrova, 1978 is quite similar in general appearance to Prozercon species. It is important to mention that the major distinctive feature in Petrova’s original description was the partial (apparent?) fusion of the opisthonotal and podonotal shields in Aleksozercon. The same phenomenon can be observed in P. semiseparatus Ujvári, 2009, but the latter lacks gv2. Apparent fusion of the dorsal shields seems to be a rare apomorphy, which may have evolved independently in both groups as a homoplasy, but further observation of Aleksozercon specimens would be necessary for a firm decision. There is a species, Mesozercon changbaiensis (Bei et al., 2002) comb. nov., which was previously described as Prozercon, which possess conspicuous pores gv2 and ventrianal setae ZV 1. I propose that this species should be transferred to the genus Mesozercon Błaszak, 1976, inasmuch as the posterodorsal muscle scars are unsclerotised and not conspicuous, therefore “dorsal cavities” characteristic for most of the Zerconidae genera are lacking, which is a relatively rare apomorphy in the family. Furthermore, other major characters of this species agree with Mesozercon, except the shape of setae r1, which is plumose in M. changbaiensis and smooth in other Mesozercon species.

The number of opisthomarginal setae often varies individually, even within a specimen, and asymmetry of this character is quite common in zerconid mites. In Prozercon, this number varies between five and nine, but specimens with five, six and nine pairs of marginal setae can be considered as aberrant. Observing several specimens of each species it is clear that basically two groups exist, the first one generally bears seven pairs of marginal setae (six R-setae), the second one generally bears eight pairs (seven R-setae). From a zoogeographic point of view it is important to note that most of the species bearing generally seven pairs of opisthomarginal setae are distributed only in the Mediterranean area, with the exception of P. sellnicki Halašková, 1963, which occurs in an area extending to Central Europe as well. Prozercon species with eight pairs of opisthomarginal setae are distributed from the boreal to the Mediterranean zone of Europe and West-Asia.