Omalogyridae

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Omalogyridae
Ammonicera minortalis (from Rolán (1992: text fig. 10, 11, 13, 15). Scale = 100 μm)

Ammonicera minortalis (from Rolán (1992: text fig. 10, 11, 13, 15). Scale = 100 μm)

Systematics
Class : Gastropoda
Subclass : Orthogastropoda
Superordinate : Heterobranchia
Order : Heterostropha
Superfamily : Omalogyroidea
Family : Omalogyridae
Scientific name of the  superfamily
Omalogyroidea
Sars , 1878
Scientific name of the  family
Omalogyridae
Sars , 1878

The Omalogyridae are a family of snails living in the sea from the order of the Heterostropha , which is classified as a Heterobranchia . It is the only family in the superfamily Omalogyroidea. These are very small forms, including what is currently (as of 2015) the smallest species of snail in the world, Ammonicera minortalis Rolán, 1992.

features

The almost planispiral and very small shells measure less than two millimeters in diameter in the adult stage, many species even less than one millimeter. The housing only has 2 to 3 turns. The protoconch , which is more or less clearly left-handed, takes about one to 1.3 turns. The right-hand twisted Teleoconch has one to one and a half turns. The housings are ammonite- shaped or lens-shaped.

The animals have no gills and no osphradia ; Instead, they have clearly protruding dorsal and ventral ciliary ligaments on the right side of the mantle cavity . The foot and mantle cavity are densely covered with glands. The head and foot are bilobed at the front end. A horny operculum sits on the back of the foot . The head tentacles are drawn out in small tips, but they can also be short and narrow. The eyes are in the center of the base of the head tentacles. The digestive tract is relatively simple. The hermaphroditic genital system is highly complex. Internal fertilization takes place. The development takes place via - in comparison to the small adult size - very large yolk-rich eggs that are enclosed in egg capsules. A fully developed young animal hatches from the egg capsule; a free larval stage is not formed. The shell is usually light to dark brown, the surface of the case is shiny.

Geographical distribution and habitat

The Omalogyridae occur worldwide mostly in shallow water near the coast. There they live in the interstices of sediments , which mainly consist of shell fragments, or on sea ​​lettuce ( Ulva lactuca ) or other algae.

Taxonomy

The taxon was established in 1878 by Georg Ossian Sars as Homalogyridae, based on Homalogyra an unauthorized emendation of the generic name Omalogyra . The position of the family within the heterobranchia is still controversial. Usually the family is placed in a monotypical superfamily Omalogyroidea, or in the Architectonoidea . According to the sperm morphology , Rissoelloidea , Omalogyroidea and Pyramidelloidea are closely related.

Currently (as of 2015) the family is assigned only three genera with 54 species. In addition, there is a not yet determined number of fossil species.

supporting documents

literature

  • Natalie Baeumler, Gerhard Haszprunar, Bernhard Ruthensteiner: 3D interactive microanatomy of Omalogyra atomus (Philippi, 1841) (Gastropoda, Heterobranchia, Omalogyridae). Zoosymposia, 1: 101-118, 2008 PDF
  • Rüdiger Bieler, Paula M. Mikkelsen: Notes on the Smallest Living Gastropod in the United States and Comments on Other Species of Omalogyridae (Heterobranchia). Nautilus, 111 (1): 1-12, 1998 PDF
  • Rudolf Kilias: Marine mussels and snails , lexicon. 340 pp., 2nd edition, Ulmer, Stuttgart 2000 (first edition 1997), ISBN 978-3-8001-3105-1
  • Emilio Rolán: The family Omalogyridae GO Sars, 1878 (Mollusca, Gastropoda) in Cuba with description of eight new species. apex 7 (2): 35-46, 1992 online at www.biodiversitylibrary.org

Individual evidence

  1. ↑ Natalie Baeumler, Gerhard Haszprunar, Bernhard Ruthensteiner: 3D interactive microanatomy of Omalogyra atomus (Philippi, 1841) (Gastropoda, Heterobranchia, Omalogyridae). Zoosymposia, 1: 01-118 2008 doi : 10.11646 / zoosymposia.1.1.9
  2. ↑ Georg Ossian Sars: Bidrag til kundskaben Norges arctic fauna, I. Mollusca regionis arcticae Norvegiae. XIII + 466 S., Brogger, Christiania, 1878. Online at www.biodiversitylibrary.org (p. 215)
  3. ↑ John M. Healey: Comparative sperm ultrastructure and spermiogenesis in basal heterobranch gastropods (Valvatoidea, Architectonicoidea, Rissoelloidea, Omalogyroidea, Pyramidelloidea) (Mollusca). Zoologica Scripta, 22 (3): 263-276, 1993 doi : 10.1111 / j.1463-6409.1993.tb00357.x

Web links

Commons : Omalogyridae  - Collection of images, videos and audio files