Processus of identification of a water mite found in Roëzé

Fig 10 - Water mite - dorsal

This water Mite was caught in Roëzé (France – Sarthe) the same day I caught a bunch of Mideopsis orbicularis, the 7th of April 2012. The length of this water mite is 815µm and the width 635 µm.

As this identification process is mainly a fail, I put it in my blog section and the real identification is given on this page.


Log of my identification process.

With the 20/25 acetabulae (fig 20), I went in the Hopkins key (1961) to try to find water mite matching this detail. The Piona conglobata female share some similarities on this criteria (but they are arranged on a triangular shape with the point in direction of the genital opening).

With this idea of Piona, I went through the plates of Soar & Williamson (1927). Here are some remarks on the plates :

  • Piona discrepans female (plate 37 fig 14) : too many acetabulae. Length up to 1.12mm.
  • Piona circularis female (plate 38 fig 1) : not the same disposition, too many acetabulae.
  • Piona rotunda female : (plate 38 fig 3) : the acetabulae are disposed on a line surrounding the genital field. Length 1.1mm.
  • Piona stjördalensis female (plate 38 fig 9) : too many acetabulae. About 1.4mm.
  • Piona variabilis female (plate 38 fig 7) : same number of acetabulae. Not the same disposition (forming a rounded shape on variabilis). Length about 1.3mm.
  • Piona uncata female (plate 38 – fig 13) : too many acetabulae
  • Piona nodata female (plate 39 – fig 2) : too many acetabulae. Not the same disposition. 1.2 to 2mm.
  • Piona clavicornis (plate 39 – fig 5) : more acetabulae. Not the same shape. Some similarities nevertheless. Up to 1.4mm
  • Piona conglobata female (plate 39 – fig 7) : same number of acetabulae. Not the same shape. Up to about 1.1mm.
  • Piona carnea female. Not illustrated. Up to 2.5mm.
  • Piona paucipaura female (plate 39 – fig 15) : same number of acetabula. Not the same shape. 1.2mm.
  • Piona rotundoides female (plate 39 – fig 17) : too many acetabula. 1.8mm.
  • Piona controversiosa (up to 1.6mm) – disparilis (up to 1.2mm) – fallax (1.36mm) – neumani (?) – laminata (1.8mm) – longipalpis (2.5 to 3mm)- coccinea (length up to 3mm) – obturbans (about 1.1mm) – (plate 40) : not the same shape and too many acetabula.

So after my water mite is very probably a Piona female but there is no match for the number and disposition of the acetabula in Soar & Williamson.

To double check, i’ve added the size of the female found in Soar & Williamson.

Soar & Williamson : Piona conglobata : antenniform bristles thin and long and curved upward. see my fig 50)

I’ve then checked the nice website of Holger Müller but none of the Piona he had match mine (clavicornis, coccinea, conglobata, nodata laminata, variabilis).

Next idea is to check the piona already found in France. I used the checklist from Smit & Gerecke (2010). Here is the list of Piona already found in France : ambigua, carnea, alpicola, uncata, clavicornis, coccinea, discrepans, disparilis, imminuta, conglobata conglobata, longipalpis, neumani, nodata nodata, obturbans, paucipora, pusilla, rotundoides, stjoerdalensis, tuberifera, variabilis.

While I’m almost lost among all these species I open a book of Wolcott (1905) and found plate XXVII – fig 86, some similarities in Piona rufa (Koch).

On this paper, I found many very good pictures of Piona. This paper include a key (from Harry Smit – 2010) for the male and female Piona. The pictures eliminate Piona nodata, Piona laminata, Piona carnea, Piona neumani, Piona stjoerdalensis, Piona coccinea.

By chance, while looking for possibilities in Piersig 1897, I found an illustration rather matching on plate IX with Curvipes thoracifer. From Piersig in Deutsch : Länge 0.83mm Breite : 0.64mm (almost perfect match).

By Googling « Curvipes thoracifer » I found a reference from Ferdinand Koenike asserting that Curvipes thoracifer was Curvipes discrepans, AKA Piona discrepans.

In the key given by Harry Smit the key point given for Piona discrepans may match : « Posterior large genital plate elliptical, with 20-25 acetabula ». This is also matching if this number of acetabula is for the 2 sides.

I also checked Smith (1976) but this paper is mainly about Pionidae larva and I didn’t get any ID idea or confirmation in it.

My next step was to look in Viets 1936 and I was rather pleased to find a new idea of identification in the family Forelia. On pages 363, the drawing of Forelia mutata is well matching my specimen and to a lesser extent the Forelia curvipalpis on page 362 is also to consider.


  • Hopkins, C.L. (1961). Key to the Water Mites (Hydracarina) of the Flatford Area. Field Studies Council.
  • Piersig,G.R. (1896-1899).Deutschlands Hydrachniden.Zoologica (download from Biodiversitylibrary)
  • Smit, H. & Gerecke, R. (2010) : A checklist of the water mites of France (acari: hydrachnidia). Acarologia 50(1): 21-91.
  • Smit, H. (2010). Macrofaunanieuwsmail 95. Link.
  • Smith, I. (1976). A study of the systematics of the water mite family Pionidae (Prostigmata, Parasitengona) (Memoirs of the Entomological Society of Canada ; no. 98)
  • Soar, C.D. & Williamson, W. (1927) – The British Hydracarina. Volume II. Ray Society, London.
  • Viets, K. (1936). VII : Wassermilben oder Hydracarina. Tierwelt Deutschlands.
  • Wolcott, R. (1905). A review of the genera of the water-mites. Transaction of the american microscopical society.

References non used but probably interesting :

  • Davids, C. & F.A.C. Kouwets (1987). The characteristics of some watermite species of the genus Piona (Acari; Hydrachnellae) with three new larval descriptions. Archiv für Hydrobiologie 110: 1-18.
  • van Haaren T (1995) Enige verschilkenmerken tussen Piona paucipora, P. variabilis en P. neumani. Intern rapport
    Zuiveringschap Hollandse Eilanden en Waarden, Rotterdam. 1 p.

Other pictures of this water mite.

Fig 20 - Water mite - ventral


Fig 30 - Water mite - Genital area


Fig 40 - Water mite - Palpi


Fig 50 - Water mite - Lateral

Fig 60 - Water mite - Dorsal




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