Armiger crista, commonly known as the Nautilus ramshorn, is a minute species of freshwater snail, an aquatic pulmonate gastropod mollusk in the family Planorbidae, the ram's horn snails.
Distribution The distribution of this species is Holarctic (spread across the northern part of the whole northern hemisphere). The distribution type is circumpolar wide-temperate, and the range includes: Czech Republic Horsák M., Juřičková L., Beran L., Čejka T. & Dvořák L. (2010). "Komentovaný seznam měkkýšů zjištěných ve volné přírodě České a Slovenské republiky. [Annotated list of mollusc species recorded outdoors in the Czech and Slovak Republics]". Malacologica Bohemoslovaca, Suppl. 1: 1-37. PDF. - least concern (LC)Juřičková L., Horsák M. & Beran L., 2001: Check-list of the molluscs (Mollusca) of the Czech Republic. Acta Soc. Zool. Bohem., 65: 25-40. Slovakia Germany Italy Netherlands Sweden The British Isles, Great Britain, Ireland See Fauna Europaea for European distribution.
Shell description The minute shell is nearly planispiral in its coiling, but the spire is actually considerably sunken rather than raised (which is usually the case with gastropods).
The shell has regular transverse ridges which form points extending beyond the main curve of the periphery of the shell.
The shell color is a translucent yellowy-brown. The maximum shell dimension is about 3 mm.
Ecology This snail lives on water plants in clear still freshwater. In Ireland it is common in medium to very small habitats including slow streams, drains and marsh and fen pools It is occasionally found in very acid waters.
This minute species, although technically a pulmonate gastropod, does not use air for respiration but instead absorbs oxygen through its mantle cavity which is full of water.
References
External links
Gyraulus crista at AnimalBase