Apogastropoda is a clade of

gastropods Gastropods (), commonly known as slugs and snails, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and from the land. Ther ...

uniting the highly diverse

Caenogastropoda Caenogastropoda is a taxonomic subclass of molluscs in the class Gastropoda. It is 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 subcla ...

and

Heterobranchia Heterobranchia, the heterobranchs (meaning "different gill"), is a taxonomic clade of snails and slugs, which includes marine, aquatic, and terrestrial gastropod molluscs. Heterobranchia is one of the main clades of gastropods. Currently Het ...

. Most caenogastropods are

sea snails Sea snails are slow-moving marine gastropod molluscs, usually with visible external shells, such as whelk or abalone. They share the taxonomic class Gastropoda with slugs, which are distinguished from snails primarily by the absence of a visibl ...

, whereas heterobranchs include not only sea snails but most species of

sea slug Sea slug is a common name for some Marine biology, marine invertebrates with varying levels of resemblance to terrestrial Slug, slugs. Most creatures known as sea slugs are gastropods, i.e. they are Sea snail, sea snails (marine gastropod moll ...

land snail A land snail is any of the numerous species of snail that live on land, as opposed to the sea snails and freshwater snails. ''Land snail'' is the common name for terrestrial molluscs, terrestrial gastropod mollusks that have gastropod shell, shel ...

, and

land slug Slug, or land slug, is a common name for any apparently shell-less terrestrial gastropod mollusc. The word ''slug'' is also often used as part of the common name of any gastropod mollusc that has no shell, a very reduced shell, or only a sma ...

Taxonomy

Apogastropoda was coined by Salvini-Plawen and Hazprunar in 1987. In their original usage, it was intended as a

paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

grouping that contained caenogastropods and non- euthyneuran heterobranchs. In 1997, Ponder and Lindberg redefined the taxon to include Euthyneura, so that it would be

monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

. The monophyly of Apogastropoda is supported by both morphological and molecular data. Phylogenetic analyses based on the mitochondrial genome have historically found Apogastropoda to be non-monophyletic, but this is considered an artifact of

long branch attraction In phylogenetics, long branch attraction (LBA) is a form of systematic error whereby distantly related lineages are incorrectly inferred to be closely related. LBA arises when the amount of molecular or morphological change accumulated within a lin ...

and the reliability of the mitochondrial genome for resolving deep relationships in molluscs has been questioned. Early analyses of the mitogenome, which recovered Heterobranchia as the sister taxon of Patellogastropoda instead of Caenogastropoda, included data from only one patellogastropod taxon, ''

Lottia digitalis ''Lottia digitalis'', commonly known as the fingered limpet or ribbed limpet, is a species of sea snail, a true limpet, a marine gastropod mollusk in the family Lottiidae. These limpets are usually found on the surface of rocks in the high inte ...

'', which has undergone a high rate of evolutionary change to its mitogenome that obscures its evolutionary relationships. Including mitochondrial genomes from more species of patellogastropod results in a monophyletic Apogastropoda being recovered, consistent with the results from other sources of data.

Description

Apogastropods are generally characterized by a single pair of head tentacles, each of which contains a nerve that is deeply forked into two parallel branches. In euthyneurans, this condition is modified so that each nerve branch forms a separate tentacle.

References

External links

Apogastropoda taxonomy at NCBI

Gastropod taxonomy at Palaeos

Gastropods in captivity

Gastropod reproductive behavior

Gastropod Neuroscience

Reconstructions of fossil gastropods

{{Taxonbar, from=Q618839 Obsolete gastropod taxa Gastropod taxonomy