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In the most primitive gastropods, however, the stomach is a more complex structure. In these species, the hind part of the stomach, where the oesophagus enters, is chitinous, and includes a sorting region lined with cilia. [1] In all gastropods, the portion of the stomach furthest from the oesophagus, called the "style sac", is lined with cilia.
The nervous system of gastropods consists of a series of paired ganglia connected by major nerve cords, and a number of smaller branching nerves. It is sometimes called ganglionic. [1] General layout of the gastropod ganglia. In most species, the brain is fused into a single, six-lobed, organ Buccal ganglia of Aplysia californica.
Gastropods have the greatest numbers of named mollusk species. However, estimates of the total number of gastropod species vary widely, depending on cited sources. The number of gastropod species can be ascertained from estimates of the number of described species of Mollusca with accepted names: about 85,000 (minimum 50,000, maximum 120,000). [9]
A siphon is an anatomical structure which is part of the body of aquatic molluscs in three classes: Gastropoda, Bivalvia and Cephalopoda (members of these classes include saltwater and freshwater snails, clams, octopus, squid and relatives). Siphons in molluscs are tube-like structures in which water (or, more rarely, air) flows.
Vision is not the most important requirement in terrestrial gastropods, because they are mainly nocturnal animals. [1] Some gastropods, for example the freshwater apple snails (family Ampullariidae) [7] and marine species of genus Strombus [8] can completely regenerate their eyes. The gastropods in both of these families have lens eyes.
It contains a vast total of named species, second only to the insects in overall number. The fossil history of this class goes back to the Late Cambrian. As of 2017, 721 families of gastropods are known, of which 245 are extinct and appear only in the fossil record, while 476 are currently extant with or without a fossil record.
Arthropods, especially detritivores in the Order Isopoda, Suborder Oniscidea (), have been shown to be able to store heavy metals in their hepatopancreas. [3] This could lead to bioaccumulation through the food chain and implications for food web destruction, if the accumulation gets high enough in polluted areas; for example, high metal concentrations are seen in spiders of the genus Dysdera ...
Because of the open circulatory system of gastropods and other molluscs, there is no clear distinction between the blood and the lymph, or interstitial fluid. As a result, the circulatory fluid is commonly referred to as haemolymph, rather than blood. The majority of gastropods have haemolymph containing the respiratory pigment haemocyanin.