Barrel snails

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Barrel snails
Tonna perdix, Lydekker R. (ed.) (1896). The royal natural history 6 (section 12): p. 382.

Tonna perdix , Lydekker R. (ed.) (1896). The royal natural history 6 (section 12): p. 382.

Systematics
Superordinate : Caenogastropoda
Order : Sorbeoconcha
Subordination : Hypsogastropoda
Partial order : Littorinimorpha
Superfamily : Cassoidea
Family : Barrel snails
Scientific name
Tonnidae
Suter , 1913
Housing by Tonna tankervillii (Hanley, 1860)
Housing by Tonna perdix

The tonnidae or barrel worm (Tonnidae) are a family of medium-sized to very large exclusively predatory marine snails . The barrel snails are found in the Indo-Pacific , East-Atlantic , the whole Mediterranean and the Adriatic . With Tonna galea (= Dolium galea) , which reaches a size of up to 25 cm, they represent the largest species of snail in the Mediterranean.

features

The thin-walled, bulbous to almost spherical shells of the barrel snails have a wavy surface due to spiraling ribs, a wide mouth cut out at the bottom with mostly thickened outer lip notched over its entire length and without a siphon channel. The elongated, egg-shaped foot is large and thick, somewhat eyelet at the front and can be swollen by the absorption of water. The flat and broad head is almost straight. The antennae are long and thin and have eyes at the thickened base. The sipho is thick and long. The proboscis (trunk) is very large and thick and can be extended beyond the length of the housing. The operculum is missing.

Like other gill snails, barrel snails are sexually separate. The male mates with the female with a penis. The eggs are laid in wide gelatinous ribbons made up of numerous egg capsules. One capsule contains around a hundred eggs, almost all of which develop into embryos. The pelagic stage of the Veliger larvae takes about 3 to 8 months before the metamorphosis into the finished snail takes place.

Way of life

Barrel snails predatory on echinoderms and mussels . They have a long, movable trunk with a terminal suction disc. A specialty in the animal kingdom is that the saliva of barrel snails and related helmet snails and triton snails contains two to four percent free sulfuric acid and aspartic acid . These acids are produced in two large pharyngeal glands and serve to paralyze prey and soften their calcareous skeleton. The snails can then tear large chunks out of their prey with two jaw plates that have been transformed into groove-shaped hooks and their rasp tongue .

Use and endangerment

The large barrel snails can be called top predators in their habitat . Because of their predatory way of life, they are the final link in the food chain and any change in the ecological balance in this structure can affect their existence. There is also a direct hazard from the trawls , in which the large barrel snails can easily get caught. They are also often collected because of their housing. The Mediterranean species Tonna galea , among others, is endangered due to overfishing .

Systematics

Bouchet and Rocroi place the helmets (Cassinae) as a subfamily to the younger (= later established) family Tonnidae. According to the IRZN, this is not correct. Millard (1997) and Riedel (2000) therefore place them in the superfamily Cassoidea . Bouchet and Rocroi list the barrel snails (Tonninae) as one of four subfamilies within the helmet snails (Cassidae). The barrel snails are viewed by the majority of authors, however, as an independent family within the superfamily Cassoidea.

There are three genera belonging to the Tonnidae family:

Individual evidence

  1. ^ 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. 66. e) Tonne (Dolium).
  2. ↑ Brehm's Thierleben s. u.

literature

  • IO Alyakrinskaya: Morphofunctional Properties of Nutrition of Certain Predatory Gastropods. Biology Bulletin. ISSN  1062-3590 . Vol. 29, no.6 / November 2002.
  • Philippe Bouchet & Jean-Pierre Rocroi: Part 2. Working classification of the Gastropoda . Malacologia, 47: 239-283, Ann Arbor 2005, ISSN  0076-2997 .
  • Victor Millard: Classification of the Mollusca. A Classification of World Wide Mollusca . Rhine Road, South Africa 1997, ISBN 0-620-21261-6 .
  • Winston Ponder & David Lindberg, Towards a phylogeny of gastropod molluscs; an analysis using morphological characters . Zoological Journal of the Linnean Society, 119: 83-265, London 1997, ISSN  0024-4082 .
  • Frank Riedel: Origin and evolution of the "higher" Caenogastropoda . Berliner Geoscientific Abhandlungen, Series E, Volume 32, Berlin 2000, 240 pages, ISBN 3-89582-077-6 .
  • Richard Semon (1890): On the purpose of excreting free sulfuric acid in sea snails. Biological Centralblatt 9, page 80.

Web links

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