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The shell ranges from 3 mm to 37 mm in diameter depending on species. Like in chitons , the head is poorly defined, and there are no eyes. The mouth is located within the animal's undeveloped head in front of its single large foot and contains a radula , a defining characteristic of the mollusca.
All known modern forms are shell-less: only some extinct primitive forms possessed valves. The group comprises the two clades Solenogastres (Neomeniomorpha) and Caudofoveata (Chaetodermomorpha), which between them contain 28 families and about 320 species. The aplacophorans are traditionally considered ancestral to the other mollusc classes.
A slug on a wall in Kanagawa, Japan.. Slug, or land slug, is a common name for any apparently shell-less terrestrial gastropod mollusc.The word slug is also often used as part of the common name of any gastropod mollusc that has no shell, a very reduced shell, or only a small internal shell, particularly sea slugs and semi-slugs (this is in contrast to the common name snail, which applies to ...
In contrast to many other mollusc classes, aplacophorans have no shell, and are instead covered by aragonitic sclerites (calcareous spicules), which can be solid or hollow. These spicules can be arranged perpendicular to one another within the cuticle to form a skeleton, stick up to form a palisade, or can lie flat against the cuticle.
The generalized mollusc is an unsegmented, bilaterally symmetrical animal and has a single, "limpet-like" shell on top. The shell is secreted by a mantle covering the upper surface. The underside consists of a single muscular "foot". [19] The visceral mass, or visceropallium, is the soft, nonmuscular metabolic region of the mollusc.
The black slug (also known as black arion, European black slug, or large black slug), Arion ater, is a large terrestrial gastropod mollusk in the family Arionidae, the round back slugs. Many land slugs lack external shells, having a vestigial shell. [2]
The mollusc (or mollusk [spelling 1]) shell is typically a calcareous exoskeleton which encloses, supports and protects the soft parts of an animal in the phylum Mollusca, which includes snails, clams, tusk shells, and several other classes. Not all shelled molluscs live in the sea; many live on the land and in freshwater.
Molluscs are a large phylum of invertebrate animals, many of which have shells. Edible molluscs are harvested from saltwater, freshwater, and the land, and include numerous members of the classes Gastropoda (snails), Bivalvia (clams, scallops, oysters etc.), Cephalopoda (octopus and squid), and Polyplacophora (chitons).