Real pear snail
| Real pear snail | ||||||||||||
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Housing of Turbinella pyrum |
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| Scientific name | ||||||||||||
| Turbinella pyrum | ||||||||||||
| ( Linnaeus , 1767) |
The real pear snail , pear vortex snail or Hindu bell ( Turbinella pyrum , Syn . : Xancus pyrum ) is a snail from the Turbinellidae family (genus Turbinella ) that is widespread in the Indian Ocean . It feeds mainly on polychaetes .
features
The large, very thick, pear-shaped snail shell of Turbinella pyrum , which in adult snails in the Gulf of Mannar reaches a length of about 8 to 29 cm, has a very wide, low thread that ends in a narrow, warty spike on the vertebra. The six to seven whorls are small and smooth at first, but then quickly increase and are flattened. They are surrounded with very fine lines. The simple seam is irregularly wavy. The very bulbous body is flattened roof-shaped at the top, almost blunt-edged and barely visible knotty in the angular area, concentrically striped in the upper area. The furrows are crossed by irregular transverse strips and furrows beginning at the growth strips. The elongated housing mouth has a curved edge, which is thick and rounded in the case of old snails, and ends in an open, striped siphon channel of approximately the same length. The columella is concave and has four oblique folds. The inner lip is only thickened here in young snails, very broad in older ones. There is a longer umbilical cord. The casing is pale brown-yellow in color, ivory-yellow in the upper part of the perimeter and darker below, the mouth is yellowish flesh-colored and white inside. The bulge is covered with one or more rows of small, sometimes only punctiform, but mostly larger, almost square brownish-red spots, which rarely extend over the whole area.
distribution
The real pear snail is native to the Indian Ocean on the coasts of India and Sri Lanka . It is mainly to be found in the Gulf of Mannar and the Palk Strait , also scattered in the Gulf of Bengal as far as Nellore ( Andhra Pradesh ), west ( Arabian Sea ) on the coast of Kerala ( Malabar coast ) and in isolated occurrences off Kathiawar ( Gujarat ).
habitat
The real pear snail lives on fine sand with a moderate amount of mud, where tube- dwelling polychaetes - especially from the family Terebellidae , which form their main food - live in large numbers. It is mainly found at depths from 10 m to at least 27 m. It rarely occurs in shallower water.
food
In addition to remains of polychaetes, algae have also been found in the intestines of Turbinella pyrum . In captivity, the snail eats not only polychaetes but also live earthworms and mussels ( Donax cuneatus, Donax faba ).
Life cycle
Like other new snails, Turbinella pyrum is sexually separated, with the females being up to one and a half times the size of the males. The main mating season is from January to March with a focus on late January to mid-February. The male mates with the female with his penis . Often a female is besieged by several males. In studies in the Gulf of Mannar , the bodies of copulating males were 5.3 to 5.7 cm long and those of the females 7 to 8 cm. The union often lasts until the first egg capsule is laid. The capsules are initially soft and pliable and turn yellow on contact with the sea water. A clutch is about 25 to 31 cm high and contains about 28 to 34 capsules. It resembles a ram's horn in shape. The development of the finished snail takes place entirely within the egg capsules. A clutch produces around 200 to 250 young animals, which can have a housing up to 15 mm long when hatched. At a temperature of 30.7 ° C, young snails with a shell length of about 9 mm and a body weight of about 0.14 g hatch after 32 to 35 days. Immediately after hatching, they begin to eat small polychaetes. After a year in the aquarium with good feeding, they reach a length of 6.2 cm and a body weight of 32 g.
Enemies
Apart from humans, drill sponges (genus Cliona ) are very important enemies of the real pear snail. If a drilling sponge grows on a snail shell, it forms tunnels in which it lives and gradually dissolves the lime. In the advanced stage, holes appear which lead to the death of the now unprotected snail.
Importance to humans
Turbinella pyrum , long known by the synonym Xancus pyrum , is collected for its case, which is sold as jewelry. In India in particular, the expensive housing is traded a lot. In addition, the meat is eaten. In India the snail is called Shankha ( Sanskrit : शंख , Śaṇkha), English Chank .
The Shankha snail shell has a religious meaning in India. The snail shell is a symbol of Vishnu and Lakshmi . Snail trumpets have been made from the case for several thousand years , most of which are decorated by carving.
The snail is traditionally brought out of the sea by divers who have to dive many meters deep. The abolition of the monopoly of the state of Tamil Nadu for the Shankha fishery in the 1990s has intensified the exploitation of the snail stocks. This also includes the lifting of the limitation of snails to be fished to a shell length of at least 5.5 cm. In the last few decades, trawling has also gained in importance. The snail populations and the average shell size have decreased. In addition, large parts of the habitat including the snail spawn have been devastated by the bottom trawls.
Due to the high demand for Shankha, attempts are being made to expand the breeding of snails. This is easier than with many other snail species because plankton-eating Veliger larvae do not have to be fed.
Individual evidence
- ↑ a b I. Jagadis, G. Syda Rao, KK Joshi, P. Kandan (2010): Fishery and population dynamics of the sacred chank Turbinella pyrum (= Xancus pyrum Linnaeus, 1758) off Kayalpattinam in the Gulf of Mannar (PDF; 258 kB) . Indian Journal of Fishery 57 (3), pp. 1-5.
- ^ C. Brüggemann (1838): The natural history in faithful illustrations and with a detailed description of the same. Eduard Eisenach publisher, Leipzig 1838. Die Weichthiere, p. 76. The real pear snail or tadpole. Murex (Turbinella) Pyrum Lam. s. Voluta Pyrum L.
- ↑ Heinrich Carl Sexton : Purpuracea Menke. Purple snails. Third division. Purple snails with an elongated base, without transverse ridges. Turbinella, Lamarck. Vortex snail. Systematic Conchylia Cabinet. Nuremberg, 1879. pp. 28f. No. 21. Turbinella pyrum , Linnaeus . Linne. The pear vortex snail.
- ↑ Carolus Linnaeus : Systema Naturae. 12th ed., Laurentius Salvius: Stockholm 1767, p. 1186, 322. Voluta , p. 1195. 433. Voluta Pyrum. V. testa obovata subcaudata, spirae anfractibus striatis, apice producto glaberrimo, columella triplicata. ... Habitat in Tranquebar . Sprengler. Testa pyriformis, undulatim striata, pallido-punctato-fasciata. Apex cylindricus basi angulatus, glaberrimus, obtusus. Cauda exserta, patula, integra.
- ↑ DW Devanesen, PI Chacko (1943): On the bionomics of the Sacred Chank, Xancus pyrum (Linn). ( Memento from September 23, 2010 in the Internet Archive ) (PDF; 154 kB) . Proceedings of the National Institute of Sciences of India, IB, pp. 141-142.
- ↑ James Hornell (1915), p. 3.
- ^ A b S. Mahadevan, K. Nagappan Nayar (1968): Notes: Underwater ecological observations in the Gulf of Mannar off Tuticorin (PDF; 209 kB) . Journal of the Marine Biological Association of India 7 (1), pp. 197-198.
- ↑ a b c A.P. Lipton, M. Selvakku (2000): Breeding, rearing and sea-ranching of chanks (PDF; 228 kB) . In: VN Pillai, NG Menon (Ed.): Marine Research and Management . Central Marine Fisheries Research Institute (Indian Council of Agricultural Research), Tatapuram (Kerala) 2000. pp. 765-774.
- ^ NV Subba Rao: Indian Seashells: Polyplacophora and Gastropoda. Zoological Survey of India, Issue 192 of Records of the Zoological Survey of India, 2003. p. 288.
- ↑ PA Thomas, KK Appukuttan, K. Ramadoss and SG Vincent (1983): Calcibiocavitological investigations (PDF; 1.5 MB). Marine Fisheries Information Service Technical and Extension Series 49, pp. 1-13.
- ↑ AP Lipton, P. Thillairajan, M. Bose, JR Ramalingam, K. Jayabalan (1996): Large-scale exploitation of sacred chank Xancus pyrum using modified trawl net along Rameswaram Coast, Tamil Nadu (PDF; 284 kB) . Marine Fisheries Information Service, Technical and Extension Series 143, pp. 17-19.
- ↑ K. Ramadoss: Gastropods , p. 206: Xancus pyrum (PDF; 1.2 MB). In: M. Mohan Joseph, AA Jayaprakash (Ed.): Status of exploited marine fishery resources of India . Central Marine Fisheries Research Institute, 2003.
literature
- James Hornell: The Indian conch (Turbinella pyrum, Linn.) And its relation to Hindu life and religion . Williams and Norgate, London 1915. ( archive.org ; PDF; 7.6 MB)
Web links
- AP Lipton: Conservation mariculture - breeding of seahorses and sacred chanks (Center for Marine Science and Technology, Manonmaniam Sundaranar University, Rajakkamangalam, 2009; PDF; 75 kB)