Raft snails

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Raft snails
Violet snail with raft, washed up on the beach in Maui, Hawaii.

Violet snail with raft on the beach of Maui ( Hawaii rinsed).

Systematics
Superordinate : Caenogastropoda
Order : Sorbeoconcha
Subordination : Hypsogastropoda
Partial order : Ptenoglossa
Superfamily : Epitonioidea
Family : Raft snails
Scientific name
Janthinidae
Gill , 1871 (1854)

The raft snails (Janthinidae) are a small family of medium-sized, exclusively marine snails with around 9 species that occur worldwide in tropical and temperate seas. The representatives of the family live pelagically on the sea surface as carnivores of cnidarians .

features

Characteristic for all representatives of the raft snail is the up to 12 cm long chitin-containing raft, formed from the body's own mucus and made of transparent, air-filled bubbles, on which the animals float on the surface of the water and are thus spread across the oceans. The slime for the raft is formed in a gland at the base of the snail. Since the worm with the ventral side and thus the housing mouth hanging up, they are reversed counter-chat advantage .

The right-hand winding, smooth shells of the raft snails are thin and fragile, so that weight is saved. While the Veliger larvae still have an operculum , this is no longer present in the adult animals.

The snails have a large head and a very agile neck. The very small eyes are at the base of the antennae. Similar to spiral staircases, the band-shaped radula has no central teeth and several hook-shaped side teeth on each side. Each side of the radula has a jaw with a smooth cutting edge, and in the Recluzia genus there are also stilettos at the exits of the salivary glands.

The snails are first males and later females. Violet snails do not have a penis, and the sperm is transferred from the male to the female in packets of seeds. In Janthina exigua and Janthina pallida , the female attaches egg capsules with a total of up to two and a half million eggs to the underside of the raft, from which free-swimming Veliger larvae hatch. Janthina janthina , on the other hand, is ovoviviparous , i. H. the eggs develop in the fallopian tube of the mother until they hatch, which the Veliger larvae leave through the sexual opening. There are no relevant studies for the genus Recluzia . This is followed by a longer phase of the Veliger than zooplankton .

At the time of metamorphosis , the juvenile snail forms a long slimy stalk with a ball of air bubbles at the end, with the help of which the animal reaches the surface where the final raft will be formed. The air-containing mucous bubbles are formed with the foot, and a bubble takes about 10 seconds. If a raft snail loses its raft, it can only form a new one if it has contact with the surface of the water and thus with the air, e.g. B. hanging on a sailing jellyfish .

Way of life, occurrence and distribution

The Janthinidae are common in tropical and temperate seas. They float on the surface of the sea with their raft and feed on pelagic cnidarians , especially sailing jellyfish and Portuguese galleys .

Systematics

According to Bouchet and Rocroi (2005), the Janthinidae family is one of three families in the superfamily Epitonioidea . The Janthinidae family includes two genera:

  • Janthina Röding, 1798 with 5 types
  • Recluzia Petit de la Saussaye, 1853 with 4 species

The two genera differ among other things in the color of the housing. These are purple for Janthina and brown for Recluzia .

About 60 species have been described for the genus Janthina , but Laursen reduced them to 5 species in a revision in 1953 based on the anatomy, the radula structure and the reproductive cycle of the snails: Janthina janthina (Linnaeus, 1758), Janthina exigua Lamarck, 1816, Janthina globosa Swainson, 1822, Janthina pallida W. Thompson, 1840 and Janthina umbilicata d'Orbigny, 1841 There are 11 species descriptions of the genus Recluzia , of which only 2 or 3 may withstand a revision.

The two genera Iodes Mörch, 1860 and Iodina Mörch, 1860 are synonyms of Janthina Röding, 1798.

literature

  • Carol M. Lalli, Ronald W. Gilmer: Pelagic Snails. The Biology of Holoplanktonic Gastropod Mollusks . Stanford University Press, Stanford (California) 1989. Chapter 2, pp. 8-26: The Janthinid Snails: Raft Builders .
  • Philippe Bouchet & Jean-Pierre Rocroi: Part 2. Working classification of the Gastropoda . Malacologia, 47: 239-283, Ann Arbor 2005 ISSN  0076-2997
  • 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 .

Web links

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

Individual evidence

  1. ↑ D. Laursen (1953): The Genus Ianthina. Dana Report 38, pp. 3-40.
  2. ^ World Register of Marine Species , World Marine Mollusca database: Janthina Röding, 1798
  3. ^ Lalli and Gilmer (1989), p. 9.