Theodoxus danubialis

Danube nerite ( Theodoxus danubialis )

The Danube nerite ( Theodoxus danubialis ) is a freshwater snail from the family of Kahn snails ( Neritidae ), which is expected to over order of Neritimorpha.

Features

The Danube nerite has a 9-13 mm wide, strongly flattened body with 2.5 and 3 turns. The top has a characteristic dark zigzag drawing on a light background. The width of the zigzag lines is variable. Occasionally, almost black specimens. The mouth is round to slightly elliptical. The lid (operculum ) is bright yellow and has a plate-like cones. The rim is brown and slightly thickened. The soft body is light with a wide foot. The antennae are long and pointed; Sitting at the base of the eyes.

Lifestyle and deposits

The Danube nerite is a freshwater snail that needs clean, oxygen-rich rivers. She lives on rocky ground and is therefore dependent on running water, since the flow keeps the gravel free of sludge deposits. It feeds mainly on diatoms ( diatoms ). Small residual populations of this species live in the Lower Bavarian Danube. For the free-flowing Danube between Straubing and Vilshofen individual finds of snail shells from recent times are known in the field of Isarmündung. In Austria it is considered in the Danube main stream already be lost. But you still occurs in the tributaries of the Danube. In Hungary there are larger populations in different rivers.

Reproduction

The Danube nerite is dioecious. The females attach the egg capsules, which contain about 30 to 70 eggs to hard substrate, often even the case of conspecifics. Within the egg capsules, however, developed only one egg; the remaining eggs act as Nähreier that are eaten by the developing young in the egg capsule. The development time is four to eight weeks. After slipping a finished young animal from the egg capsule.

Systematics and Nomenclature

It is found both the spelling Danube nerite and Danube nerite; However, as recommended by Jungbluth and Knorre spelling is Danube nerite. The species was described in 1828 by Carl Jonas Pfeiffer under the name Nerita danubialis first time scientifically. Today the species is subdivided into three subspecies: the Nominatunterart Theodoxus danubialis danubialis (C. Pfeiffer, 1828), Theodoxus danubialis stragulatus (C. Pfeiffer, 1828) and Theodoxus danubialis cantianus ( Kennard & Woodward, 1924).

Endangering

The species is regarded as endangered in Germany, Austria and the Czech Republic.

Others

The Latin name Theodoxus danubialis mean as much as "God's gift to the Danube " or " The praise of God in the Danube". The striking case of the Danube nerite played in the early cultures on the Danube an important role as jewelry and grave goods. Original auger housing can be found for example in the exhibition of natural history collection of the Humboldt University of Berlin and the world Burgkloster. Today, the patterned snail shells symbol of resistance against the expansion Danube in Lower Bavaria has become.