Snail King
As screw kings is called single screw , the housing ( "houses") are wound in the mirror image, not species-specific direction.
The winding direction of snail shells is generally defined by the direction of the helix that the pitch describes from the inside to the outside, if you look at the shell of the snail from the side on which the inner (closed) end of the snail is located (increasing clockwise = right-handed ). The easiest way to do this is to look at the housing with the mouth pointing forwards and the tip of the shell pointing upwards (apex). If the muzzle is now to the right of the shell's longitudinal axis (spindle), the housing is right-handed.
Roman snails usually have right-hand wound shells. After they succeeded for the first time in reproducing snails with left-handed shells, British researchers Angus Davidson and Philippe Thomas estimate the relative frequency of individuals with left-handed shells to be a maximum of 1: 40,000.
In such animals, all organs (e.g. heart, respiratory and genital orifices) are reversed (mirror-inverted). Due to their rarity and the opposite position of their sexual organs, the Roman snail kings normally cannot mate.
Snail kings of the Roman snail are occasionally exhibited in natural history collections; Such a case is in the Bodensee-Naturmuseum in Konstanz.
This phenomenon , known as situs inversus (a. Heterotaxia ), also occurs in humans , for example in the context of Kartagener's syndrome .
The US-American geneticist Alfred Henry Sturtevant suspected in the 1920s after investigations of the Alpine mud snail ( Radix labiata , then Lymnaea peregra ) that the direction of the coiling of snails is inherited in a matroclinic dominant recessive manner. However, Davidson and Thomas came to the conclusion that genetic inheritance plays no role in the winding direction of the housing. Rather, the left turn comes about by chance during embryonic development.
Davidson and Thomas assumed a specimen of the red Roman snail named Jeremy for their breeding experiments . Using the hashtag #snaillove, they published a campaign, based on which additional copies were sent to them. After their breeding attempts produced three generations of snails, they published their results.
Most known species of snail usually have right-hand wound shells; in some species, however, left-handed houses are the norm. Most door snail species (Clausiliidae), for example, are left-wound, with the exception of some species that are right-wound, which is atypical of the group. It also happens that right- and left-wound species belong to the same group of land snails. So within the wolverine snails (Enidae) z. As the March snail ( Zebrina detrita ) a rechtsgewundenes, the smaller Tetradentate Wolverine screw ( Jaminia quadridens ) but linksgewundenes housing.
In a number of historical copper engravings and woodcuts , in contrast to nature, left-wound snails are shown, because the copper and wooden plates have to be engraved in a mirror-inverted manner in order to create the original image in the print. To do this, the artists have to mentally mirror the templates (real copies or drawings), which is difficult, or orientate themselves on their mirror images. Many artists may not even have been aware that one direction predominates in nature.
Web links
- The winding direction of the snail shell
- Snail kings (with pictures)
- The genetics of the shell twist (with crossbreeding scheme)
Individual evidence
- ↑ a b c d Angus Davison, Philippe Thomas: Internet 'shellebrity' reflects on the origin of rare mirror-image snails . In: Biology Letters . The Royal Society, June 3, 2020, doi : 10.1098 / rsbl.2020.0110 (English, royalsocietypublishing.org [accessed June 5, 2020]).
- ↑ Andrea Kamphuis (2008): Of real and false snail kings