Gastropod snails

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Gastropod snails
Oxynoe olivacea in a saltwater aquarium

Oxynoe olivacea in a saltwater aquarium

Systematics
Trunk : Molluscs (mollusca)
Class : Snails (gastropoda)
Subclass : Orthogastropoda
Superordinate : Heterobranchia
Order : Hind gill snails (Opisthobranchia)
Subordination : Gastropod snails
Scientific name
Sacoglossa
H. von Ihering , 1876

The gastropod snails ( Sacoglossa , often incorrectly also Saccoglossa) are a subordinate of the hind- gill snails (Opisthobranchia). The suborder includes around 700 species of nudibranch, half-nudibranch and shell snails living in the sea. The name gastrointestinal snail is derived from a sack-shaped formation of the throat in which the front end of the single-row rasping tongue (radula) is located.

features

The representatives of the Sacoglossa are mostly small animals. The housing is thin-walled, egg-shaped and / or mostly reduced. However, there are still forms that can retract completely into the housing. In most species, however, it is more or less reduced and the animals are called "nudibranchs". In some families , the housing is covered by the foot flaps ( parapodia ). Some species can also use these footrests for swimming. The occurrence of genera with two-lobed shells (in the Juliidae family ) among the gastropods is unusual . These snail shells are similar to the shells of mussels . The left shell flap is homologous to the shells (casings) of the other snails , the right one is an additional formation of the shell . The head has one or two pairs of tentacles , e.g. T. are reduced. In front of the radula there is a sack-shaped blind sac of the throat, in which the front end of the radula is stuck. The radula consists of only one central tooth per row. Over time, the worn out rows of radulas collect in the sack; the sack therefore gets bigger with increasing age.

Way of life and occurrence

The animals are mainly found in the algae zone of the sea coasts. The snails feed on algae, the chloroplasts of which they ingest and store in their skin or enlarged midgut glands ( kleptoplastids ). In addition to the strong green color that many species develop as a result, their body shape itself is similar to algae. The photosynthesis of the chloroplasts ingested also gives the animals nutrients that they can live on for a while. The chloroplasts die off after a while and have to be replaced by the ingestion of new algae. Many species use green algae of the genus Caulerpa . Other species also feed on other green algae, brown algae , diatoms (diatoms), seaweed, and others. According to their way of life, most of the species live in shallow coastal waters between sea grasses and algae. A few species have also made their way into fresh water.

Tribal history

Despite this diversity , the sacoglossa are phylogenetically as a monophyletic group whose main common feature ( synapomorphy ) is the throat sack. This group represents a basic taxon for the cladistics of snails.

Systematics

Spiral-shaped packet of Oxynoe olivacea eggs on the inner pane of an aquarium
Elysia crispata from the Caribbean

The taxonomy of snails is subject to revision and change. Therefore there are different classifications. The one that goes back to J. Thiele (1929–1935) is usually considered classic . It was recognized until the 1990s. A more modern and the last one established on the basis of purely morphological approaches is that of Ponder & Lindberg (1997). The current system is phylogenetically oriented and goes back to Bouchet & Rocroi (2005).

Systematics according to Bouchet & Rocroi (2005)

The family Placobranchidae according to Rang (1829) and the family Elysiidae according to Forbes & Hanley (1851) are considered synonyms .

Individual evidence

  1. ^ SI Williams, DI Walker: Mesoherbivore-macroalgal interactions: feeding ecology of sacoglossan sea slugs (Mollusca, Opisthobranchia) and their effects on their food algae . Oceanography and Marine Biology: an Annual Review 1999, 37, pp. 87-128.
  2. ^ Ponder, WF & Lindberg, DR (1997). "Towards a phylogeny of gastropod molluscs: an analysis using morphological characters" . Zoological Journal of the Linnean Society 119 (2): 83-265. doi : 10.1111 / j.1096-3642.1997.tb00137.x
  3. ↑ Bouchet, P. & Rocroi, J.-P .: Part 2. "Working classification of the Gastropoda". Malacologia , 47: 239-283; 2005
  4. ↑ Bouchet, P. & Rocroi, J.-P. (Ed.): Frýda, J., Hausdorf, B., Ponder, WF, Valdés, Á. & Warén, A. (2005). "Classification and nomenclator of gastropod families". Malacologia: International Journal of Malacology 47 (1-2). ConchBooks: Hackenheim, Germany. ISBN 3-925919-72-4 . ISSN  0076-2997 . 397 pp. http://www.vliz.be/Vmdcdata/imis2/ref.php?refid=78278
  5. ↑ Poppe, GT & Tagoro, SP 23 February 2006. "The New Classification of Gastropods gemäß to Bouchet & Rocroi, 2005". PDF ( Memento of the original from September 27, 2007 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / www.journal-malaco.fr

literature

Web links

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