Notaspidea, also known as the sidegill slugs, is an artificial grouping of

sea slugs Sea slug is a common name for some marine invertebrates with varying levels of resemblance to terrestrial slugs. Most creatures known as sea slugs are gastropods, i.e. they are sea snails (marine gastropod mollusks) that over evolutionary t ...

which is now split into two unrelated groups, the Umbraculida and the Pleurobranchomorpha.

Taxonomic history

Notaspidea, also known as the sidegill slugs, was a

suborder Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...

which included both

sea slug Sea slug is a common name for some marine invertebrates with varying levels of resemblance to terrestrial slugs. Most creatures known as sea slugs are gastropods, i.e. they are sea snails (marine gastropod mollusks) that over evolutionary ...

s and sea snails or false

limpet Limpets are a group of aquatic snails that exhibit a conical gastropod shell, shell shape (patelliform) and a strong, muscular foot. Limpets are members of the class Gastropoda, but are polyphyletic, meaning the various groups called "limpets" ...

s, marine

opisthobranch Opisthobranchs () is now an informal name for a large and diverse group of specialized complex gastropods which used to be united in the subclass Opisthobranchia. That taxon is no longer considered to represent a monophyletic grouping. Euopis ...

gastropod molluscs in the subclass

Orthogastropoda 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 (Ponder & Lindberg, 1997). This taxon is no longer used according ...

. However, in the newer taxonomy of Bouchet & Rocroi (2005), the families Umbraculidae and Tylodinidae belong to the superfamily Umbraculoidea

Dall Dall may refer to: People * Anders Bendssøn Dall (died 1607), Danish Lutheran bishop * Bobby Dall (born 1963), American musician * Caroline Healey Dall (1822–1912), American feminist writer *Clarrie Dall (1887–1953), Australian footballer * C ...

, 1889, part of the clade Umbraculida. Grande ''et al.'' (2004) found Umbraculoidea to be a sister clade to the

Cephalaspidea The order Cephalaspidea, also known as the headshield slugs and bubble snails, is a major taxon of sea slugs and bubble snails, marine gastropod mollusks within the larger clade Euopisthobranchia.Jörger K. M., Stöger I., Kano Y., Fukuda H. ...

(Acteonoidea excluded). The families Tylodinidae and

Umbraculidae Umbraculidae are a Taxonomy (biology), taxonomic family (biology), family of unusual sea snails or limpets, marine (ocean), marine opisthobranch gastropod molluscs in the clade Umbraculida. Distribution This family has a global distribution in t ...

have large limpet-like external shells and a small

mantle A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that. Mantle may refer to: *Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear **Mantle (vesture), an Eastern Orthodox ve ...

, while the species in the family Pleurobranchidae have a prominent mantle and an internal shell that becomes reduced or is lost in adults. Many species produce mantle secretions as a chemical defense against predators

Families

* Pleurobranchidae Menke, 1828 * Tylodinidae Gray, 1847 *

, 1889

Notes

References

* * Powell A. W. B., ''New Zealand Mollusca'', William Collins Publishers Ltd, Auckland, New Zealand 1979 {{Taxonbar, from=Q141484 Obsolete gastropod taxa