Water mites is a group of about 5000 species of mites. Scientific name of them is Hydrachnidia or Hydrachnidia or Hydracarina or Hydrachnellae. They are usually very small and this is one of them. I found it in my freshwater aquarium on Helisoma anceps. It is so small that I had to use lens to verify, that the small dot on the shell is a water mite. The water mite is in the centre of the photo. It is on the mantle edge near the aperture. Detail cropped from the previous photo: You can compare the size of the water mite with two Ferrissia fragilis snails on the top of the shell of Helisoma anceps. Both of these freshwater snail species are of North American origin and both belong to the same family Planorbidae. Ferrisia fragilis can reach 3.2 mm maximum shell length, but I think my snails are a bit smaller. The water mite is about 0.5 mm or smaller. It was actively moving on the snail. The dot in the centre of the photo is the water mite: I do not know the origin of the water mite. I found only one in my aquarium meantime.
Helisoma anceps lays eggs in gelatinous translucent clusters.
This cluster is taken shortly after eggs laying. I think it is about the second or the third day. There are seen five small dot-like embryos:
This is yet another cluster of nine eggs shortly before hatching. Eight hours later all snail were hatched. The length of this whole cluster is 4 mm and it is attached to a stem of a common freshwater plant from the genus Hydrocotyle. There are seen shells of all nine embryos and there are seen heads with eyes of three snails in the first row:
Clausilia rugosa is a clausiliid living in forests on limestone rocks. Its shell measure up to 9.5 mm and it is the smallest species in the genus Clausilia.
The locality is Průchodnice Nature Reserve in the Czech Republic. It is a deciduous forest reserve with European beech Fagus sylvatica on limestone rocks. There are also remnants of caves by Upper Paleolithic men (Magdalenian culture). It is a nice reserve especially in April:
Hlaváč J. Č. (2002) Molluscan fauna of the Javoříčský Karst (Czech Republic, central Moravia). Malacological Newsletter, 20: 93–105.
Horsák M., Juřičková L. & Picka J. (2013) Měkkýši České a Slovenské republiky. Molluscs of the Czech and Slovak Republics. Kabourek, Zlín, 264 pp. (in Czech and English). page 89.