Gastropoda

Thesaurus

Noun

Gastropoda - snails and slugs and their relativesclass Gasteropoda, class Gastropoda, GasteropodaMollusca, phylum Mollusca - gastropods; bivalves; cephalopods; chitonsgastropod, univalve - a class of mollusks typically having a one-piece coiled shell and flattened muscular foot with a head bearing stalked eyesfamily Haliotidae, Haliotidae - abalonesfamily Strombidae, Strombidae - the family of conchsfamily Limacidae, Limacidae - slugsfamily Neritidae, Neritidae - neritidsBuccinidae, family Buccinidae - whelksCymatiidae, family Cymatiidae - tritonsfamily Naticidae, Naticidae - moonshellsfamily Littorinidae, Littorinidae - periwinkleslimpet - any of various usually marine gastropods with low conical shells; found clinging to rocks in littoral areasfamily Patellidae, Patellidae - marine limpetsfamily Fissurellidae, Fissurellidae - marine limpetsAncylidae, family Ancylidae - freshwater gastropodOpisthobranchia, subclass Opisthobranchia - gastropods having the gills when present posterior to the heart and having no operculum: includes sea slugs; sea butterflies; sea haresAkeridae, family Akeridae - bubble shellsorder Pulmonata, Pulmonata - large order of gastropods usually breathing by means of a lung-like sac comprising most land snails and slugs and many freshwater snailsorder Pectinibranchia, Pectinibranchia - large order of gastropods comprising univalve mollusks that have a single gill resembling a combAmphineura, subclass Amphineura - a class of Gastropodaclass - (biology) a taxonomic group containing one or more orders

Gastropoda

The largest and most varied class in the phylum Mollusca, possibly numbering over 74,000 species and commonly known as snails.

General characteristics

The shell is in one piece which, in the majority of forms, grows along a turbinate (equiangular) spiral (see illustration), but which is modified into an open cone in various limpets or is secondarily lost in various slugs.

Longitudinal section ground through the shell of a specimen of Conus spurius to reveal the central columella and spiral of whorls expanding to the aperture

All gastropods, at some time in their phylogeny and at some stage in their development, have undergone torsion. The process does not occur in any other mollusks. It implies that the visceral mass and the mantle shell covering it have become twisted through 180^° in relation to the head and foot. As a result of torsion, all internal organs are twisted into a loop. Similarly in gastropods, the mantle cavity (the semi-internal space enclosed by the pallium or mantle) containing the characteristic molluscan gills (ctenidia) has become anterior and placed immediately above and behind the head. The most primitive gastropods retain a pair of aspidobranch (bipectinate or featherlike) gills, each with alternating ctenidial leaflets on either side of a ctenidial axis in which run afferent and efferent blood vessels. Lateral cilia on the faces of the leaflets create a respiratory water current (toward the midline and anteriorly) in the direction opposite to the flow of blood through the gills, to create the physiological efficiency of a countercurrent exchange system.

Classification and diversity

The usual systematic arrangement of the class Gastropoda involves three somewhat unequal subclasses. The first, the largest and most diverse, is the subclass Prosobranchia, which is made up largely of marine snails all retaining internal evidence of torsion. Prosobranchs are divided into at least four orders: Archaegastropoda, Caenogastropoda, Neritida, and Patellogastropoda; three superfamilies remain to be assigned to one of the four orders, and may each comprise a distinct order. The other two subclasses (Opisthobranchia and Pulmonata) are each considerably more uniform than the subclass Prosobranchia and, in both, the effects of torsion are reduced or obscured by secondary processes of development and growth.

More than half of all molluscan species are gastropods, and they encompass a range from marine zygobranchs, which can be numbered among the most primitive of all living mollusks, to the highly evolved terrestrial air-breathing slugs and snails. Pulmonates and certain mesogastropod families are the only successful molluscan colonizers of land and fresh waters.

Fossils

Fossil gastropods have a long geologic history, being common throughout the Paleozoic and increasingly abundant in the Mesozoic and Cenozoic. All three subclasses are known in the fossil record; many superfamilies, particularly prosobranchs, are extinct. Average duration of a genus has been estimated to range from 30,000,000 to 90,000,000 years.

Marine gastropods are important stratigraphic indicators in Cenozoic strata and locally are abundant in Cretaceous rocks. They are less common and less useful in the Jurassic and Triassic. Although individual genera have stratigraphic utility within the Paleozoic, it is only in the Ordovician that they are significant for correlation. See Mollusca

Gastropoda

[ga′sträp·ə·də] (invertebrate zoology) A large, morphologically diverse class of the phylum Mollusca, containing the snails, slugs, limpets, and conchs.

Gastropoda

Gastropoda

Gastropoda

General characteristics

Classification and diversity

Fossils

Gastropoda

Gastropoda

Gas·trop·o·da

Gastropoda

Synonyms for Gastropoda

noun snails and slugs and their relatives

Synonyms

Related Words