Zerconella Willmann, 1953

Ujvári, Zsolt, 2010, Zerconella Willmann, 1953, a forgotten group of Zerconidae (Acari: Mesostigmata), Zootaxa 2558, pp. 33-47 : 35-36

Genus Zerconella Willmann, 1953

Zercon (Zerconella) Willmann, 1953: 473 ; Petrova, 1977: 591; Karg, 1993: 313.

Diagnosis. Peritrematal shields truncate behind fourth pair of coxae, and separated by triangular slit from body margin behind posterior peritrematal setae. Two pairs of peritrematal setae present, anterior peritrematal setae short, smooth or very finely pilose, posterior peritrematal setae considerably longer (3–10 times as long as anterior setae), finely pilose or smooth, apically tapering. Both pairs inserted dorsally on peritrematal shield. Peritremes short, reaching only posterior edge of third pair of coxae. Adgenital gland openings present, situated on conspicuous platelets. One pair of post-genital sclerites often present. Ventri-anal shield caudally fused to opisthonotal shield. Anterior margin of ventri-anal shield with two pairs of setae. Ventri-anal pores situated posterolaterally to adanal setae. Epistome with two pairs of longer central points and several shorter spines. Anterior margin of podonotum sloping gradually, setae j1 inserted dorsally. Setae z1 absent. Margin of opisthonotum with 7–8 pairs of setae.

Notes on the genus. On the basis of a detailed observation of Zerconella leitnerae specimens collected in Slovenia and Croatia ( Ujvári, 2009, 2010), I raise the subgenus Zercon (Zerconella) Willmann, 1953 ( Figs 1, 2 ) to full generic rank because of the following features: posterior peritrematal setae are very long, smooth or very finely pilose, apically tapering and inserted dorsally in Zerconella ; but shorter, usually apically pilose or feathered, often with hyaline ending and inserted ventrally in Zercon ; peritremes are short (neotenic) (15–20 μm), reaching only the posterior edge of the third pair of coxae in Zerconella ; peritremes are longer (60–80 μm), reaching the anterior edge of the third pair of coxae in Zercon ; post-genital sclerites are usually present in Zerconella , absent in Zercon ; the epistome has four long, central points and several shorter spines in Zerconella ; usually three long, central points of which the medial one is often apically bifurcate or trifurcate in Zercon . The genus Zercon is heterogeneous in important generic characters, such as the number of setae on the anterior margin of the ventri-anal shield and the distribution of dorsal glands, therefore it can not be objectively compared with the genus Zerconella in its current form on the basis of these features.

Regarding the genus Metazercon, Błaszak (1975a) the author described similar generic characters of peritrematal shields, peritrematal setae, peritremes, number of ventri-anal setae, adgenital and post-genital attributes to that of Zerconella leitnerae . However Błaszak omitted to compare Metazercon with the former subgenus Zerconella . In addition Błaszak (1975a) mentioned two characters which would distinguish the type species of Metazercon from Zerconella leitnerae . The number of marginal setae is eight in Metazercon , seven in Zerconella leitnerae , and the former has a deep incision on posterolateral side of peritrematal shields which is absent in the latter. Later, examining other specimens Halašková (1979) recognised that Metazercon species can have seven or eight pairs of marginal setae on the opisthonotum, and the incision of in the peritrematal shields is often absent. Dorsal gland openings are minute in most of the species, some of them often not visible, but it seems that the second pair of opisthonotal pores (gdJ2) is associated with setae J2 (on a line connecting setae J2 and Z2), while the third pair (gdJ4) is associated with caudodorsal lobes in the Asian species. It is interesting that some of the species lack one pair of J-setae. Unfortunately no larvae or protonymphs are known from the redefined group, while ontogenetic studies of different Zerconidae genera show that setae J2–5 are present in larval stage and J1 appears in protonymphs ( Lindquist & Moraza 1998). Presumably the four pairs of larval J-setae are present in each Zerconella species, while in species having only four pairs of J-setae the protonymphal J1 setae are lacking. However the absence of setae J 1 may be an important derivative character. The zoogeographic distribution of Zerconella species suggests that the former character appeared independently in the European and some Asian species, as an evolutionary convergence.

Besides the above-mentioned characters it is important to note that each species of the redefined genus Zerconella has an oblong shape, a relatively small body-size (230–350 μm) and two or four pairs of strongly sclerotised dorsal cavities. Setae of each species are smooth or very finely pilose, setiform, and often elongate. The genital opening of known males is situated below the line of sternal setae st3.

Figures

FIGURES 1 – 2. Ventral idiosoma. 1. Zerconella; 2. Zercon.