|Various shells of Vetigastropoda|
|Subclass:|| Vetigastropoda |
|3,700 extant species|
Vetigastropoda is a major taxonomic group of sea snails, marine gastropod mollusks that form a very ancient lineage. Taxonomically the Vetigastropoda are sometimes treated as an order, although they are treated as an unranked clade in Bouchet and Rocroi, 2005.
Vetigastropods are considered to be among the most primitive living gastropods,and are widely distributed in all oceans of the world. Their habitats range from the deep sea to intertidal zones. Many have shells with slits or other secondary openings. One of their main characteristics is the presence of intersected crossed platy shell structure. Most vetigastropods have some bilateral asymmetry of their organ systems.
Vetigastropods range in size from approximately 0.08 in (2 mm) long in the case of Scissurelloidea or Skeneoidea, to more than 11.8 in (300 mm) in length, as with the Haliotoidea. External colours and patterns are typically drab, but such groups as the Tricolioidea and some Trochoidea and Pleurotomarioidea have bright colours and glossy shells. The clade is characterized by having an intersected crossed platy shell structure.
Shells range from elongate turret-shaped structures, to near-spherical. Shell sculpture varies greatly from simple concentric growth lines, which may or may not be barely visible on the shell surface, to heavy radial and axial ribbing. The shell aperture is normally oval, and often tangential to the coiling axis. Most species have an operculum (a small lid-like organ). Within the shell, Vetigastropods have a single pair of cephalic tentacles, and a distinct snout containing the mouth. The lateral sides of the body typically have sensory epipodial tentacles.
Vetigastropods are found throughout all oceans of the world, including tropical areas, temperate regions, and under polar ice.
Vetigastropods are present in most marine environments from intertidal zones to the deep sea. They exist on rocky substrates, in soft sediments, and some have been found at deep-sea hydrothermal vents and cold seeps.
Most vetigastropods are dioecious, although some deep-sea varieties are hermaphrodites. Vetigastropods usually eject their gametes directly into the sea for fertilization, thus there is no courtship or mating between individuals for most species.
Vetigastropods typically feed on such organisms as bryozoans, tunicates, and sponges. Several species such as Haliotoidea and Trochoidea have evolved to feed directly on such plant material as algae and marine angiosperms. Deep-sea vetigastropods typically consume sediment.
Vetigastropods normally have very small eggs that produce lecithotrophic (yolk feeding) or non-feeding larvae. Many vetigastropods secrete egg envelopes and have glandular pallial structures that produce masses of jelly-coated eggs.
Larger species typically have yearly cycles of spawning, and produce millions of eggs per reproductive season. Smaller species produce fewer eggs, but can spawn year round.
The Vetigastropoda have been referred to as a superorder as recently as at least 2007, by M. Harzhauserand in 2005 by D. Heidelberger and L. Koch following Ponder & Lindberg, 1997, although Bouchet & Rocroi, 2005 refer to this group simply as a clade, leaving taxonomic determination as a future option. The World Register of Marine Species (WoRMS) follows Bouchet & Rocroi regarding the taxonomic content of the Gastropoda but gives ranks to the higher taxa and defines Vetigastropoda as a subclass.
Bouchet & Rocroi, 2005 treats the Vetigastropoda as a major clade and as a sister clade to the Caenogastropoda but includes the Vetigastropoda in what are referred to as Basal taxa that are certainly Gastropoda. Ponder & Lindberg, 1997 previously assigned the Vetigastropoda, as a superorder, to the Subclass Orthogastropoda. Phylogenetic analysis indicates that this taxon is one of the four natural groups within the Gastropoda: Vetigastropoda, Caenogastropoda, Patellogastropoda, and Heterobranchia. Research on the mitochondrial genome arrangement has shown that the Vetigastropoda (and Caenogastropoda) mostly retain the ancestral gene arrangement.
Superfamilies within the Vetigastropoda include:
Neogastropoda is a clade of sea snails, both freshwater and marine gastropod molluscs.
Orthogastropoda was a major taxonomic grouping of snails and slugs, an extremely large subclass within the huge class Gastropoda according to the older taxonomy of the Gastropoda.
Heterobranchia, the heterobranchs, is a taxonomic clade of snails and slugs, which includes marine, aquatic and terrestrial gastropod mollusks.
Caenogastropoda is a taxonomic clade, a large diverse group which are mostly sea snails and other marine gastropod mollusks, but also includes some freshwater snails and some land snails. The clade is the most diverse and ecologically successful of the gastropods.
Neomphaloidea is a superfamily of deep-sea snails or limpets, marine gastropod mollusks. Neomphaloidea is the only superfamily in the order Neomphalida.
Chilodontaidae is a taxonomic family of mostly small deepwater sea snails, marine gastropod molluscs in the clade Vetigastropoda.
Trochoidea is a superfamily of small to very large vetigastropod sea snails with gills and an operculum. Species within this superfamily have nacre as the inner shell layer. The families within this superfamily include the Trochidae, the top snails. This superfamily is the largest vetigastropodan superfamily, containing more than 2,000 species.
Lepetodrilidae is a family of small, deep-sea sea snails, hydrothermal vent limpets, marine gastropod mollusks in the clade Vetigastropoda.
Anatomidae is a family of minute sea snails, marine gastropod mollusks in the clade Vetigastropoda.
Phasianellidae common name the "pheasant shells" or "pheasant snails" is a family of small sea snails with calcareous opercula, marine gastropod mollusks in the clade Vetigastropoda.
The taxonomy of the Gastropoda, as revised by Winston Ponder and David R. Lindberg in 1997, is an older taxonomy of the class Gastropoda, the class of molluscs consisting of all snails and slugs. The full name of the work in which this taxonomy was published is Towards a phylogeny of gastropod molluscs: an analysis using morphological characters.
Apogastropoda was previously used as a major taxonomic grouping of sea snails, marine gastropod molluscs. This infraclass mostly consisted of marine limpets and operculate snails. At least 20,000 species were considered to exist within the two clades that were included, Heterobranchia and Caenogastropoda.
Neritimorpha is a taxonomic grouping, an unranked clade of snails, gastropod mollusks. This grouping includes land snails, sea snails, some deepwater limpets, and also freshwater snails. This clade used to be known as the superorder Neritopsina.
Turbinoidea was a superfamily of small to large sea snails, marine gastropod mollusks in the clade Vetigastropoda. But it has become an available name, because it is no longer used in the current taxonomy of gastropods sensu Williams et al. (2008).
Pleurotomarioidea is a superfamily of small to large marine gastropods included in the order Pleurotomariida of the subclass Vetigastropoda.
Scissurelloidea is a taxonomic superfamily of minute sea snails, marine gastropod mollusks or micromollusks in the clade Vetigastropoda.
Seguenzioidea is a superfamily of minute to medium-sized sea snails, marine gastropod mollusks in the clade Vetigastropoda.
This overview lists proposed changes in the taxonomy of gastropods at the family level and above since 2005, when the taxonomy of the Gastropoda by Bouchet & Rocroi (2005) was published. In other words, these are recent updates in the way various groups of snails and slugs are classified.
Margaritidae is a family of small sea snails, marine gastropod mollusks in the superfamily Trochoidea.
Trochida is an order of small to very large vetigastropod, Recent and extinct sea snails with gills and an operculum.
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