Photo of the day (54): eggs of Ancylus fluviatilis

Adults of freshwater gastropod Ancylus fluviatilis have a cap-like shell. But shells of its embryos are a bit different. You can find eggs of Ancylus fluviatilis in spring and in early summer on stones in streams. I found these eggs in northern Bohemia in June.

Eggs are laid in capsules. There are 9-12 eggs in each capsule.

egg capsules of Ancylus fluviatilisThere can be seen foot, eyes and tentacles under stereo microscope easily in this state of development. There are also ribs on the shell, that resemble ribs of some Patella species to me. I have taken the photo in situ.

eggs of Ancylus fluvitilisI found no images of eggs of Ancylus fluviatilis for comparison on the internet after a brief search.


Species summary for Ancylus fluviatilis. AnimalBase, last change 26 October 2013, accessed 8 July 2016.

Streit B. (1976). Energy flow in four different field populations of Ancylus fluviatilis (Gastropoda-Basommatophora). Oecologia, 22(3): 261-273.

Embryonic development of Bithynia tentaculata

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:

Bithynia tentaculata eggsEggs are usually laid in two rows. There is seen a bit compressed shape of eggs, when you will look out from the side view:

Bithynia tentaculataIt 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).

Day 1:

Bithynia tentaculata

Day 2:

Bithynia tentaculata

Day 3:

Bithynia tentaculata

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.

Day 4:

Bithynia tentaculata

Day 5:

Bithynia tentaculata

Day 6:

Bithynia tentaculata

Day 7:

Bithynia tentaculata

There is clearly visible a shell by naked eye since the seventh day.

Day 8:

Bithynia tentaculata

Eyes, foot, head and snout are clearly recognizable.

Day 9:

Bithynia tentaculata

Day 10:

Bithynia tentaculata

Tentacles are visible easily.

Day 11:

Bithynia tentaculata

Day 12 – hatching:

Bithynia tentaculata

The first hatched snails:

Bithynia tentaculata

The diameter of hatching snails is 1.2 mm and their weight is 0.25 mg (Negus 1998).

Day 13:

Bithynia tentaculataThere 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:

Bithynia tentaculataReferences

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:
10.1080/00219266.1998.9655588 abstract

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

Photo of the day (49): Ambigolimax valentianus

Ambigolimax valentianus is a land slug from the family Limacidae. Its native distribution includes Iberian Peninsula only, but it is spreading in many other countries as an invasive species. It can live in greenhouses and similar habitats in cold areas only. It lives in greenhouses in Central Europe too. It is a pest in greenhouses and it is able to overpopulate and then it can be a serious pest. It can reach the length up to 70 mm.

Various views of the slug:

Ambigolimax valentianus

Ambigolimax valentianus

Ambigolimax valentianus

Ambigolimax valentianusThe foot is light gray:

Ambigolimax valentianusThere exist two forms of Ambigolimax valentianus: a form with two dark lateral bands and a a spotted form. The spotted form looks like this. It looks a bit yellow on the photo, but it is caused by the sunglight.

Ambigolimax valentianusIts eggs look like this. I found those eggs below the bowl for the potted plant.

Ambigolimax valentianusNotice the juvenile slug in the front. It is interesting that its egss will not survive temperatures above 33 °C.

A juvenile slug:

Ambigolimax valentianusAnother photo with juvenile slugs:

Ambigolimax valentianusThis species is also known as Lehmannia valentiana. In fact I did not known, that it could be placed in the genus Ambigolimax up today.

So I searched for reasons of its generic placement:

Klee et al. found out based on molecular phylogeny research of cytochrome-c oxidase I (COI) genes, that the genus Lehmannia is diphyletic in 2005. She also repeated the information in her thesis in 2013.

Rowson et al. confirmed such placement also according to the COI genes analysis in 2014. By the way, they did not comment this species in the PLoS article anyhow. They just shown the cladogram on the figure 5.

The results are:

Lehmannia marginata (O. F. Müller, 1774) still belong to the genus Lehmannia Heynemann, 1863, because it is the type species of the genus.

Lehmannia valentiana (Férussac, 1822) belong to the genus Ambigolimax Pollonera, 1887 as a Ambigolimax valentiana (Férussac, 1822). It is the type species of the genus Ambigolimax.

Lehmannia nyctelia (Bourguignat, 1861) also belong to the genus Ambigolimax as Ambigolimax nyctelius (Bourguignat, 1861).

There is a question, where will belong other 13 European species of Lehmannia. Especially those ones, whose reproductive system is not known.


Horsák M., Dvořák L. & Juřičková L. (2004) Greenhouse gastropods of the Czech Republic: current stage of research. Malacological Newsletter, 22: 141–147, page 143.

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 163.

Klee B., Falkner G. & Haszprunar G (2005). Endemic radiations of Limax (Gastropoda: Stylommatophora) slugs in Corsica – they came twice. In: Burckhardt D (ed.), 8. Jahrestagung der Gesellschaft für biologische Systematik, Basel 13.-16. September 2005, Abstracts of talks and posters: p.78. Basel (Naturhistorisches Museum). Organisms Diversity and Evolution 5, Electr. Suppl. 13: 75.

Nitz. B. (2013). Integrative systematics and biogeography of Limax (Gastropoda: Stylommatophora). Dissertation Thesis, Ludwig-Maximilians-Universität, München, 133 pp., page 105.

Rowson B., Anderson R., Turner J. & Symondson W. O. C. (2014). The slugs of Britain and Ireland: undetected and undescribed species increase a well-studied, economically important fauna by more than 20%. PLoS ONE 9(4): e91907. doi:10.1371/journal.pone.0091907

Stojnić B., Vukša M., Jokić G. & Čkrkić M. (2011). First record of introduced valencia slug, Lehmannia valentiana (Férussac, 1822), in Serbia. Pesticidi i fitomedicina, 26(3): 213–220. doi:10.2298/PIF1103213S

Udaka H., Mori M., Goto S. G. & Numata H. (2007). Seasonal reproductive cycle in relation to tolerance to high temperatures in the terrestrial slug Lehmannia valentiana. Invertebrate Biology, 126(2): 154–162.

Photo of the day (47): Lithoglyphus naticoides

Lithoglyphus naticoides is a freshwater snail. Its distribution is Pontic and Danubian.

Shells from my collection comes from Danube river in Slovakia. The apertural view of the shell looks like this. The width of the shell is 8.5 mm and the height of the shell is 8.5 mm:

shell of Lithoglyphus naticoidesOblique view of the same shell:

an oblique view of the shell of Lithoglyphus naticoidesIt lives on the muddy bottom, and it can not lay egg capsules on stones. Therefore is lay egg capsules on shells of other Lithoglyphus naticoides snails. Remains of egg capsules on the shell of Lithoglyphus naticoides:

the shell of Lithoglyphus naticoides with egg capsulesthe shell of Lithoglyphus naticoides with egg capsulesDried egg capsules that have a dried embryo inside:

the shell of Lithoglyphus naticoides with egg capsulesthe shell of Lithoglyphus naticoides with egg capsulesthe shell of Lithoglyphus naticoides with egg capsules

The width of the following shell is 7.0 mm and the height of the shell is 7.0 mm.

apertural view of the shell of Lithoglyphus naticoidesapical view of the shell of Lithoglyphus naticoideslateral view of the shell of Lithoglyphus naticoidesumbilical view of the shell of Lithoglyphus naticoidesI wanted to see a color photo of an operculum of Lithoglyphus naticoides, but I found color drawings on the internet only and black-and-white photo of an operculum in books. So I made few photos of an operculum of Lithoglyphus naticoides.

The width of the operculum is 3.0 mm and the height of the operculum is 4.0 mm. It is the operculum from the shell above. Outer side of the operculum:

outer side of an operculum of Lithoglyphus naticoidesInner side of the operculum:

inner side of an operculum of Lithoglyphus naticoidesReferences


Photo of the day (44): eggs of Helisoma anceps

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:

eggs of Helisoma ancepsAnother cluster of eggs contains six more developed embryos:

eggs of Helisoma ancepsThis 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:

eggs of Helisoma anceps

Photo of the day (38): eggs of Physa acuta

Physa acuta (or Physella acuta according European malacologists) is a very common freshwater snail. It is non-indigenous in Europe, originally from the North America.

It can be often found in highly eutrophic water reservoirs such as ponds for intensive aquaculture with common carps like this one in the South Moravia:
pond 01
pond 02

Notice, that there are no wetland plants on banks.

There were many Physa acuta snails and many of its eggs on stones in the water. There are 7-50 eggs (Beran 1998) or 7-53 eggs (Glöer 2002) in gelatinous egg capsules. In-situ photo of eggs of Physa acuta (I have taken the stone out of water, of course.):
Eggs of Physa acutaEggs seems to be in very early development phase (probably less than 5 days old).


(in Czech) Beran L., 1998: Vodní měkkýši ČR. – Metodika Českého svazu ochránců přírody č. 17, Vlašim: ZO ČSOP Vlašim, 113 pp., page 83.

(in Czech) Beran L., 2002: Vodní měkkýši České republiky – rozšíření a jeho změny, stanoviště, šíření, ohrožení a ochrana, červený seznam. [Aquatic molluscs of the Czech Republic – distribution and its changes, habitats, dispersal, threat and protection, Red List]. – Sborník přírodovědného klubu v Uh. Hradišti, Supplementum 10, 258 pp., pages 197-198.

(in German) Glöer P. 2002: Die Süßwassergastropoden Nord- und Mitteleuropas. Die Tierwelt Deutschlands, ConchBooks, Hackenheim, 326 pp., ISBN 3-925919-60-0, page 238.

Further reading:

September 26, 2014: The Egg Masses of Freshwater Pulmonate Snails. The Blog of the FWGNA Project.

Perez, K. E. & Sandland G. (last change May 21, 2014, accessed November 1, 2014) Illustrations of common aquatic snail egg masses in Wisconsin. Key to Wisconsin Freshwater Snails.

Photo of the day (34): Theodoxus fluviatilis

Theodoxus fluviatilis is a freshwater snail living in rivers and brackish waters in Europe. It belong to nerites, the family Neritidae.

Malacological books usually depict Theodoxus fluviatilis like a shell only. The apertural view:

Theodoxus fluviatilis 12

The width of this shell is 8 mm and the height of the shell is 6 mm. Shells are sometimes corroded. The lateral view:

Theodoxus fluviatilis 13

There are remnants of two egg capsules on the shell. Snails lays eggs on solid things like stones, empty shells and shells of live Theodoxus. It is useful because such eggs are much more guarded than other eggs on non-living things.

The shell can be closed by the calcareous operculum (this operculum belong to the above shell). The length of the operculum is 4 mm and the width of the operculum is 3 mm including the rib. Outer side of the operculum:

Theodoxus fluviatilis 14 operculum

Inner side of the operculum shows the rib and some depression near the rib.

Theodoxus fluviatilis 15 operculum

Another shell of Theodoxus fluviatilis: the width of this shell is 8.5 mm and the height of the shell is 6 mm. There are also two remnants of egg capsules.

Theodoxus fluviatilis 11

Live nerite snails are not easy to watch, because they are tightly attached to stones and they usually stretch tentacles and eyes only. The width of the shell is 7 mm and the height of the shell is 5 mm.

Theodoxus fluviatilis 09

When the snail is not crawling, its foot is rounded as a suction cup:

Theodoxus fluviatilis 10

Another Theodoxus fluviatilis snail with a different pattern on the shell. Such variability is typical for nerites and these variable patterns developed for crypsis (crypsis is a type of camouflage). The width of the shell is 7.5 mm and the height of the shell is 5.5 mm.

Dorsal view:

Theodoxus fluviatilis 03

Right side view:

Theodoxus fluviatilis 01

Frontal view:

Theodoxus fluviatilis 02

Two left side views:

Theodoxus fluviatilisTheodoxus fluviatilis 07

Ventral view of crawling snail (there is a bubble):

Theodoxus fluviatilis 06

Species in the Neritidae family have one gill (ctenidium) for breathing on the left side of the body. It is in the mantle cavity. The gill is called bipectinate, that means that it have two margins toothed like a comb. I was lucky to get one photo of a gill of a live snail though the partly translucent thick shell:

Theodoxus fluviatilis 04

Detail cropped from the previous photo:

Theodoxus fluviatilis 05


Barroso C. X., Matthews-Cascon H. & Simone L. R. L. 2012: Anatomy of Neritina zebra from Guyana and Brazil (Mollusca: Gastropoda: Neritidae). Journal of Conchology 41(1): 49-64.
(I consider this reference useful for the terminology of anatomy of nerites.)