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Pionacercus cf. vatrax 24-05-2015
Pionacercus cf. vatrax
(Female, 0.85 mm)

This picture shows the bottom side of the watermite described of the previous page. There are some disturbing dust particles. The shape of the epimers is very similar tot that of Piona species. But here the genital plates each carry only three acetabula (the 'discs') -and on every Piona species there are more. The fourth epimers have very short medial sides, making them somewhat triangular in shape. The genital opening is long and (almost) reaches the third epimers. The frontal sclerite is not large. The acetabula are large and bulge out over the plates on some places. These are characteristics of Pionacercus vatrax (Viets, 1936; Besseling, 1964; van der Eijk, 1977; Davids, 1979). Not definitive, so I put a cf. in the name. Viets (1936) notes 660 µm for the length of the female, but other references over 900 µm. On the palps a small cone is visible on P-IV, I don't know if that checks with the species. On the picture below a detail of the acetabula.


Pionacercus cf. vatrax detail acetabula 24-05-2015

The acetabula of the other Pionacercus species are relatively smaller. The acetubala on the corner position are somewhat larger then the other four on our specimen, while on Tiphys pistillifer, a species that looks much like the one here, the top acetabula are the largest (Besseling, 1964, fig.185 and 191; and van der Eijk, 1977, drawings on page 73 en 75). But, on the contrary, Viets (1936) notes that on P. vatrax the top acetabula are the largest.


The male: The acetabular plates of the male (not pictured) are joined together and the third and fourth epimers are touching in the middle. Compared to the females the males are a half-length lesser in size when fully grown. On the fourth pair of legs there are special parts for gripping and controlling the legs of the female during the mating, just like all Pionides. On P. vatrax the fourth member of those legs (IV-P-4) carries a spur (Viets, 1936; Besseling, 1964).





Pionacercus cf. vatrax wrinkled 25-05-2015

Wrinkled. The picture at left shows the mite on a leaf of Hornwort: within two days it's healthy berry shape changed in that of a raisin. Soon there was hardly any life in it. I wonder if the longevity was surpassed, or if the mite has been damaged, or maybe even sucked out by it's colleague species that shared the small dish (Hydrochoreutes krameri, Limnesia koenikei). Piersig  (1897) noted that in captivity his Pionacercus leuckarti specimens perished in a short time.


About the name Pionacercus I couldn't find much. Many of the Piona‑likes with six acetabula were gathered under the genus name Acercus. As knowledge progressed they had to be regrouped and I suppose that Piersig has smelted the names Piona and Acercus into a new name. To make it even more complicated: the vatrax species later was put in a new subgender: Pionacercopsis, meaning: 'looks like Pionacercus'. The species addition vatrax seems to mean something like: 'with bad or deformed feet' and might be chosen in respect of the last legs of the male, that seem deformed by the spur on IV-P-4.





Click the picture below to see the first page on this watermite.

Pionacercus cf. vatrax 24-05-2015
the top side



References:

To the watermites REFERENCE LIST.



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rev. 09-06-2015

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