Gastropoda


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Related to Gastropoda: Echinodermata, class Gastropoda, Brachiopoda

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 apertureenlarge picture
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.
References in periodicals archive ?
The brood size had significant effects on proportions of Araneida, Gastropoda, Hymenoptera and Orthoptera (P = 0.
Gastropoda larvae (53-500 mm) was appeared in the ponds at 3 28 days of culture period and exists till end of culture period in aged ponds, whereas, it was not significant in new ponds.
GASTROPODA (Class) ARCHAEOGASTROPODA (Order) Haliotidae Haliotis lamellosa Lamarck Fissurellidae Fissurella sp.
8 67 Decopoda 1 [less than]1 17 Conchostraca 1 [less than]1 17 Gastropoda 26 8 100 Planonbidae Diptera 1 [less than]1 17 Hemiptera 2 [less than]1 17 Trichoptera 2 [less than]1 33 Odanata 1 [less than]1 17 Coleoptera 3 [less than]1 17 Haliplidae Insect parts 7 2.
Revision des Nassariidae (Mollusca: Gastropoda, Prosobranchia) de l'Afrique occidentale.
Distributions and geographical relationships of the polygyrid land snails (Mollusca, Gastropoda, Polygyridae) of Arkansas.
Gastropoda and Pelecypoda), one southern cricket frog (Acris gryllus gryllus), and unidentified invertebrate parts (Table 1).
Pontos 1 2 3 4 5 Annelida Hyrudinea 0 0 0 13 3 Oligochaeta 97 180 259 0 20 Mollusca Bivalve 241 88 99 0 10 Gastropoda 25 2 433 4 20 Plathyelmintes Turbellaria 48 7 178 0 28 Artropoda Crustacea Aeglidae 2 5 1 0 6 Hyallelidae 5 0 0 0 21 Aracnida Acari 5 1 21 0 16 Aracnidae 1 0 0 0 1 Insecta Collembola 73 33 4 0 8 Coleoptera Elmidae 575 164 1.
Dina parva Erpobdella punctata Mooreobdella Mooreobdella fervida Mooreobdella microstoma Glossiphoniidae Helobdella Helobdella stagnalis Placobdella unidentified leeches X X leech cocoons Phylum Mollusca Gastropoda Ancylidae Ferrissia C Hydrobiidae Amnicola X Lymnaeidae X Lymnaea Physidae C Aplexa Physa X X Physella Planorbidae Gyraulus X Helisoma Planorbula X Promenetus X Promenetus?
Suspension feeding with the gill, however, has evolved multiple times within the Gastropoda (Declerck 1995), most notably in the Family Calyptraeidae, including the genus Crepidula (Orton 1912b, Purchon 1977, Newell & Kofoed 1977a, Newell & Kofoed 1977b, Chaparro et al.