The mucus secreted by the foot contains fibres that help prevent the slug from slipping down vertical surfaces. Slugs also produce thick mucus that coats the whole body of the animal. The thin mucus spreads from the foot's centre to its edges, whereas the thick mucus spreads from front to back. Slugs produce two types of mucus: one is thin and watery, and the other thick and sticky. ![]() Internally, slug anatomy clearly shows the effects of this rotation-but externally, the bodies of slugs appear more or less symmetrical, except the pneumostome, which is on one side of the animal, normally the right-hand side. Like all other gastropods, they undergo torsion (a 180° twisting of the internal organs) during development. In drier conditions, they hide in damp places such as under tree bark, fallen logs, rocks and man-made structures, such as planters, to help retain body moisture. Many species are most active just after rain because of the moist ground. They must generate protective mucus to survive. Slugs' bodies are made up mostly of water and, without a full-sized shell, their soft tissues are prone to desiccation. Adult Philomycidae, Onchidiidae and Veronicellidae lack shells.Īn active Ambigolimax slug in Fremont, California An internal shell is present in the Limacidae and Parmacellidae. This organ generally serves as storage for calcium salts, often in conjunction with the digestive glands. Vestigial shell: Most slugs retain a remnant of their shell, which is usually internalized.Around the edge of the foot in some slugs is a structure called the 'foot fringe'. It simultaneously secretes a layer of mucus that it travels on, which helps prevent damage to the foot tissues. Like almost all gastropods, a slug moves by rhythmic waves of muscular contraction on the underside of its foot. Foot: The bottom side of a slug, which is flat, is called the 'foot'.Keel: Some species of slugs, for example Tandonia budapestensis, have a prominent ridge running over their back along the middle of the tail (sometimes along the whole tail, sometimes only the final part).Tail : The part of a slug behind the mantle is called the 'tail'.This opening is known as the pneumostome. On one side (almost always the right hand side) of the mantle is a respiratory opening, which is easy to see when open, but difficult to see when closed. Mantle: On top of the slug, behind the head, is the saddle-shaped mantle, and under this are the genital opening and anus.The upper pair is light sensing and has eyespots at the ends, while the lower pair provides the sense of smell. Tentacles: Like other pulmonate land gastropods, the majority of land slugs have two pairs of 'feelers' or tentacles on their head.The external anatomy of a slug includes the following: Superfamily Quijotoidea Jesús Ortea and Juan José Bacallado, 2016.Superfamily Strophocheiloidea Thiele, 1926.Superfamily Staffordioidea Thiele, 1931.Superfamily Plectopylidoidea Moellendorf, 1900.Superfamily Orthalicoidea Albers-Martens, 1860.Superfamily Limacoidea Rafinesque, 1815.Superfamily Helixarionoidea Bourguignat, 1877.Superfamily Helicoidea Rafinesque, 1815.Superfamily Gastrodontoidea Tryon, 1866.Superfamily Dyakioidea Gude & Woodward, 1921.Superfamily Achatinoidea Swainson, 1840.Superfamily Cochlicopoidea Pilsbry, 1900.Superfamily Achatinelloidea Gulick, 1873.The family Ellobiidae are also polyphyletic. It appears that pulmonates are paraphyletic and basal to the opisthobranchs, which are a terminal branch of the tree. The taxonomy of this group is in the process of being revised in light of DNA sequencing. snails whose shells are too small for them to retract fully into) and slugs. A third family, the Sigmurethra, contains various clades of snails, semi-slugs (i.e. Of the six orders of Pulmonata, two – the Onchidiacea and Soleolifera – solely comprise slugs. The shell-less condition has arisen many times independently as an example of convergent evolution, and thus the category "slug" is polyphyletic. Thus, the various families of slugs are not closely related, despite a superficial similarity in the overall body form. Various taxonomic families of land slugs form part of several quite different evolutionary lineages, which also include snails. 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 semislugs (this is in contrast to the common name snail, which applies to gastropods that have a coiled shell large enough that they can fully retract their soft parts into it). ![]() Slug, or land slug, is a common name for any apparently shell-less terrestrial gastropod mollusc.
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