腹足纲纲

生活在海水中的被称为海螺或海蛞蝓，例如：宝螺科、凤螺科以及拥有剧毒的芋螺科，生活在淡水中的淡水螺类，例如：田螺或称螺蛳、尖尾螺、囊螺、椎实螺、福寿螺、钉螺、苹果螺等等，以及生活在陆地上的蜗牛和蛞蝓。

特征

腹足纲物种具有明显且发达的头部，腹面有肥厚而广阔的足，所以得名；身体有内脏的部分扭转，因此左右不对称；外面有介壳一枚或无壳。绝大多数的腹足纲物种的介壳都呈螺旋形，当遇到危险的时候会将柔软的身体缩进壳中。也有一些壳退化消失或仅在体内残留，通常被称为蛞蝓。

具贝壳腹足类的贝壳螺旋方式可分为左旋跟右旋，区分方式为壳顶朝上，壳口面朝自己时，壳口在壳轴右边就是右旋，反之则称为左旋。一般通常为右旋壳，只有大约5%的现代腹足类是左旋壳。

栖息地

腹足纲在全世界范围内分布，包括海洋（约30,000种）、淡水（约5,000种）和陆地（约30,000种）等，从靠近南极和北极的寒冷地区到热带地区都有分布。

可以适应非常多样的生存环境，从花园、森林、沙漠到山区，从沟渠、河流到湖泊，从河口、泥滩、布满岩石的潮间带、沙底的潮下带到深海，还有些营寄生。

Gastropods (; previously known as Univalves; class Gastropoda) are a vast and diverse group of invertebrates within the phylum Mollusca, comprising the animals commonly known as snails and slugs. With an estimated 65,000 to 80,000 living species, they form the second-largest animal class after the insects. The fossil record of gastropods extends back to the Late Cambrian. As of 2017, 721 families are recognized—476 extant (some with fossil representatives) and 245 extinct known only from fossils.

Gastropods inhabit an extraordinary range of environments, including marine, freshwater, and terrestrial ecosystems. They occur in gardens, woodlands, deserts, mountains, rivers, lakes, estuaries, mudflats, intertidal zones, the deep sea, hydrothermal vents, and even in parasitic niches.

The term snail generally refers to gastropods with a large external shell into which the body can fully retract, while slugs have no shell or a small internal one, and semislugs can only partially withdraw into their reduced shell. Marine gastropods include familiar forms such as abalones, conches, periwinkles, whelks, and cowries, whose shells are usually coiled in adulthood. In contrast, limpets and related groups coil their shells only in the larval stage, retaining a simple conical form as adults.

Because of their vast diversity, gastropods exhibit remarkable variation in anatomy, behavior, feeding, and reproduction, making broad generalizations difficult. Gastropods remain one of evolution's most successful and adaptable animal lineages.