Piona clavicornis (Müller, 1776) – female – Identification almost certain

Fig 10 - Piona clavicornis female - Dorsal

This nice water mite was caught the 1st of May 2012 in a small permanent pond in Cerfontaine in Belgium. Length 1250 µm and width 1035 µm. Stored in vial B003.

Description of Piona clavicornis in Soar & Williamson 1927.

 Other names..

  • Hydrachna clavicornis
  • Nesoea aduncopalpis
  • Curvipes aduncopalpis
  • Piona aduncopalpis
  • Piona clavicornis

Body of the female

  • Up to 1.4mm in length and about 1 mm  in breadth. This one is smaller 1250:1035
  • Outline a broad oval, with a slight emargination at the anterior end, between the short and stumpy antenniform bristles. See fig 10.
  • Colour light red or reddish brown.
  • Dorsal patches dark brown. Not on mine.
  • Malpigian vessel light yellow, showing irregularly through the darker markings. See fig 10.
  • Legs a straw yellow or with the palpi and epimera of a brownish tint.
  • Eyes dark red, standing back from the body-margin.


  • Second segment about three time as thick as adjacent segments of first pair of legs. See fig 10.
  • Extensor surface of segment so long as to cause distal end to stand vertically over distal end of flexor surface, thus giving rise to the characteristic hooked appearance of palpi.
  • Third segment very short, causing the fourth segment to lie close down over first and second segments.
  • Fourth segment very long and very slender, without the papillae usually found in other species, but with two long hairs, one behind the other.
  • Fifth segment short, ending in two blunt claw.

Epimera. W

  • Epimera standing only a little from edge of the body an occupying most of anterior half of ventral surface. See fig 20.
  • Edges of plates thickened.


  • Legs with some short, for the most part pectinate bristles.
  • Swimming hair sparse.

Genital area.

  • Genital plates entirely absent.
  • From seven to twelve acetabula lying free on the skin, for the most part about the posterior half of the genital aperture. See fig 30 – 10/11 acetabula on each side.
  • On either side of the anterior end of aperture two or three short hairs with one on each side at the posterior end. See fig 30 the white spot on my picture.


  • Müller, O.F. (1781) : Hydrachnae, quas in aquis Daniae palustribus. Lipsiæ
  • Soar, C.D. & Williamson, W. (1927) – The British Hydracarina. Volume II. Ray Society, London. Page 171 + plate 39 fig 5&6).

Other pictures of this Piona clavicornis.

Fig 20 - Piona clavicornis - Ventral

Fig 30 - Piona clavicornis female - Genital area

Side notes.

I’ve found the first drawing of Pional Clavicornis in Müller (1781).

Müller Piona clavicornis Tab VI P100


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