Planorbarius corneus


Planorbarius corneus, common name the great ramshorn, is a relatively large species of air-breathing freshwater snail, an aquatic pulmonate gastropod mollusk in the family Planorbidae, the ram's horn snails, or planorbids, which all have sinistral or left-coiling shells.
The shell of this species appears to be dextral in coiling, even though it is in fact sinistral or left-handed.

Distribution

Planorbarius corneus is distributed from western Europe, through central Europe and into the Caucasus, north into Siberia and south into the Middle East. In western Europe, it has been recorded in Belgium, France and the British Isles. It is not found in Spain, but it has been recorded on some Spanish and Portuguese Atlantic islands, including Madeira, the Azores, the Canary Islands. In the Nordic countries, it has been recorded in Denmark, Finland, Sweden and Norway. Its range extends through central Europe into southern Europe and eastern Europe and the Caucasus. The species is also found in western Asia, having been recorded in Kazakhstan, Iran, western regions of Russia, Turkey, Turkmenistan and Uzbekistan.
Additionally, as the species is sometimes sold in the aquarium trade, it is also found outside of its main range in small ponds where they have been released or placed.

Description

All species within family Planorbidae have sinistral shells.
Planorbarius corneus is the largest European species of ramshorn snail, with a shell typically measuring across when fully-grown.
The coiled shell has between 3 and 4.5 rounded whorls with deep sutures, the last whorl predominating. The upper side is weakly depressed and the lower side is deeply depressed. There is no keel. The shell is light yellowish with a brown, reddish or greenish periostracum, radially and spirally weakly striated. The aperture is wide and almost circular. The animal is brown or reddish.

Habitat

This large planorbid is found in water which is still, or only moving slowly, where there is a good growth of many different kinds of pond weeds, and where there are high levels of calcium dissolved in the water.
P. corneus under high temperatures has been studied by Kartavykh & Podkovkin.

Reproduction

Reproduction in spring and autumn at water temperatures above 15 °C, eggs are laid in mostly elongate capsules of 8–15 mm width, each strain containing 12-40 eggs, fixed to aquatic plants, embryos are reddish with transparent shells, juveniles hatch after 14–16 days, life span up to 3 years. Self-fertilization is possible, one single released animal can establish a stable population, but only 5% of the juveniles in self-fertilized eggs will hatch.

Parasites

This species of snail functions as a host for several parasite species: