Bithynia tentaculata is a well known freshwater snail from the family Bithyniidae. It occurs in the Palearctic. Females lay eggs and the development lasts few weeks depending on the water temperature. It hatch after 12-14 days at the temperature 25 °C (Cather & Verdonk 1974). I had temperature 26 °C in my aquarium, so my snails hatched out in the 12th day.
This is how they look like shortly before hatching:
Eggs are usually laid in two rows. There is seen a bit compressed shape of eggs, when you will look out from the side view:
It will go though the cleavage, blastula, gastrula in the first two days. This very early development was studied by various scientists (Erlanger 1892, Van Dam 1986).
Then it will form a radula, shell, nervous system, tentacles, ctenidium, heart, foot, snout and other organs. The shell is translucent, so if you would watch the embryo in the microscope, then there would be ctenidium and heart easily recognisable.
There is clearly visible a shell by naked eye since the seventh day.
Eyes, foot, head and snout are clearly recognizable.
Tentacles are visible easily.
Day 12 – hatching:
The first hatched snails:
The diameter of hatching snails is 1.2 mm and their weight is 0.25 mg (Negus 1998).
There left only empty egg cases and incorrectly developed embryos in the 13th day.
So this is a brief insight how Bithynia tentaculata develops and how you can see it by naked eye or by magnifying lens. But it is a worth to use microscope.
When it will be lucky and if no predator will eat the juvenile snail, it will grow into a snail like this:
Cather J. N. & Verdonk N. H. (1974). “The development of Bithynia tentaculata (Prosobranchia, Gastropoda) after removal of the polar lobe“. Journal of embryology and experimental morphology, 31(2): 415-422.
Erlanger R. (1892). “Beiträge zur Entwicklungsgeschichte der Gastropoden”. Mittheilungen aus der Zoologischen Station zu Neapel 10: 376-404. Plate 25-26.
Negus M. R. (1998). “A Life Table for the fresh water mollusc Bithynia tentaculata (L.)”. Journal of Biological Education, 32(1): 14-23, DOI:
Van Dam W. I. (1986). “Embryonic development of Bithynia tentaculata L. (Prosobranchia, Gastropoda). I. Cleavage”. Journal of Morphology 188(3): 289-302. DOI: 10.1002/jmor.1051880304 abstract