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I’d like to tell you about snail. Recently we’ve known about Gastropoda on invertebrate zoology’s. And this Friday we have test on this topic. So, let’s refresh our memory!
Kingdom Metazoa
Phylum Mollusca
Class Gastropoda
Gasrtopoda or gastropods, more commonly known as snails and slugs, are a large taxonomic class within the phylum Mollusca. The class Gastropoda includes snails and slugs of all kinds and all sizes from microscopic to large. There are many thousands of species of sea snails and sea slugs, as well as freshwater snails, freshwater limpets, land snails and land slugs.
The class Gastropoda 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. There are 611 families of gastropods, of which 202 families are extinct and appear only in the fossil record.
Gastropoda (previously known as univalves and sometimes spelled Gasteropoda) are a major part of the phylum Mollusca and are the most highly diversified class in the phylum, with 60,000 to 80,000 living snail and slug species. The anatomy, behavior, feeding and reproductive adaptations of gastropods very significantly from one group to another. Therefore, it is difficult to state many generalities for all gastropods.
The class Gastropoda has an extraordinary diversification of habitats. Representatives live in gardens, in woodland, in deserts, and on mountains; etc and other ecological niches, including parasitic ones.
Anatomy
Most gastropods are hermaphrodites.
Snails are distinguished by an anatomical process known as torsion, where the visceral mass of the animal rotates 180° to one side during development, such that the anus is situated more or less above the head.
The effects of torsion are primarily physiological - the organism develops an asymmetrical nature with the majority of growth occurring on the left side. This leads to the loss of right-paired appendages (e.g., ctenidia (comb-like respiratory apparatus), gonads, nephridia, etc.). Furthermore, the anus becomes redirected to the same space as the head.
Gastropods typically have a well-defined head with two or four sensory tentacles with eyes, and a ventral foot. The foremost division of the foot is called the propodium. Its function is to push away sediment as the snail crawls. The larval shell of a gastropod is called a protoconch.
Sensory organs and nervous system
The upper pair of tentacles on the head of snail has eye spots, but the main sensory organs of the snail are sensory receptors for olfaction, situated in the epithelium of the tentacles.
Sensory organs of gastropods include olfactory organs, eyes, statocysts and mechanoreceptors. Gastropods have no hearing.
The majority of gastropods have simple visual organs, eye spots either at the tip or base of the tentacles.
Digestive system
The radula of a gastropod is usually adapted to the food that a species eats.
Many marine gastropods are burrowers, and have a siphon that extends out from the mantle edge. They use the siphon primarily to "taste" the water to detect prey from a distance.
Respiratory system
Almost all marine gastropods breathe with a gill, but many freshwater species, and the majority of terrestrial species, have a pallial lung.
Circulatory system
Gastropods have open circulatory system and the transport fluid is hemolymph. Hemocyanin is present in the hemolymph as the respiratory pigment.
Excretory system
The primary organs of excretion in gastropods are nephridia, which produce either ammonia or uric acid as a waste product. The nephridium also plays an important role in maintaining water balance in freshwater and terrestrial species.
Vocabulary
Lateral view
дыхательная пора
половое отверстие
Internal view
открытая кровеносная система
дыхательный пигмент
Phylum – тип
Limpet – морское блюдеко
The fossil – ископаемые остатки
Extinct –вымереть
The most highly devirsified class –
самый распространенный класс
Hermaphrodites – гермафродиты
Burrowers – землерои
Freshwater – пресноводные
Terrestrial - земляные