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Gastropods such as abalone and keyhole limpets have two gills, which is believed to be the arrangement in the earliest fossil gastropods. The water current to supply these gills is evacuated through a slit or notch in the upper surface of the shell, below which the anus opens. In most other gastropods, the right gill has been lost.
A ctenidium is a respiratory organ or gill which is found in many molluscs. This structure exists in bivalves, cephalopods, polyplacophorans (chitons), and in aquatic gastropods such as freshwater snails and marine snails. [1]
Gastropods (/ ˈ ɡ æ s t r ə p ɒ d z /), commonly known as slugs and snails, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (/ ɡ æ s ˈ t r ɒ p ə d ə /). [5] This class comprises snails and slugs from saltwater, freshwater, and from the land.
Snails have complex organ systems and anatomies that differ greatly from most animals. Snails and most other Mollusca share three anatomical features; the foot, the mantle, and the radula. Foot: The foot is a muscular organ used by Gastropods for locomotion. Gastropods' stomachs are located within their foot.
In many marine gastropods where the siphon is particularly long, the structure of the shell has been modified in order to house and protect the soft tissue of the siphon. This shell modification is known as the siphonal canal. For a gastropod whose shell has an exceptionally long siphonal canal, see Venus comb murex.
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 gills (g), digestive gland (dg), adductor muscle (am), epipodial tentacles (ept), right mantle lobe (rml), eyespot (es), cephalic tentacles (ct) and left mantle lobe (lml) are indicated. The hepatopancreas , digestive gland or midgut gland is an organ of the digestive tract of arthropods and molluscs .
The majority of gastropods have haemolymph containing the respiratory pigment haemocyanin. This is a copper-containing protein that helps to carry oxygen, and gives the haemolymph a pale blue colour. In the freshwater Planorbid snails, however, the haemocyanin is replaced by haemoglobin , and thus their haemolymph is red rather than blue.