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The red slug (''Arion rufus''), also known as the large red slug,''Arion'' (''Arion'') ''rufus'' (Linnaeus 1758), Large red slug
MolluscIreland. National Museums Northern Ireland. 2010.
chocolate arion''Arion rufus''.
Integrated Taxonomic Information System (ITIS). and European red slug,Rosetta, R

Pacific Northwest Nursery IPM. Oregon State University.
is a species of land
slug 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 ...
in the family
Arionidae Arionidae, common name the "roundback slugs" or "round back slugs" are a taxonomic family of air-breathing land slugs, terrestrial pulmonate gastropod mollusks in the superfamily Arionoidea. Distribution The distribution of this family of slu ...
, the roundback slugs.


Description

Slugs in the genus ''Arion'' have the
pneumostome The pneumostome or breathing pore is a respiratory opening of the external body anatomy of an air-breathing land slug or land snail. It is a part of the respiratory system of gastropods. It is an opening in the right side of the mantle of a ...
(respiratory pore) in the front part of the
mantle A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that. Mantle may refer to: *Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear **Mantle (vesture), an Eastern Orthodox ve ...
and a round back without a
keel The keel is the bottom-most longitudinal structural element on a vessel. On some sailboats, it may have a hydrodynamic and counterbalancing purpose, as well. As the laying down of the keel is the initial step in the construction of a ship, in Br ...
. ''Arion rufus'' is one of the largest species in the genus, up to 150 mm extended. As an adult it lacks the lateral bands found in many smaller congeners, but in some forms the sides are paler than the back. The body colour is often reddish, sometimes vividly so, but orange, yellowish, brown and greyish forms are also usual, and some individuals may be black. The foot fringe is vertically striped and is often a different colour than the back. The head and tentacles are often darker than the rest of the body. The mucus is sticky and colourless or orange. Externally the species is not reliably distinguishable from several other species, including '' A. ater'' and '' A. vulgaris'', and can be difficult to distinguish from less closely related species such as '' A. flagellus'', especially in the Iberian Peninsula where further similar species exist. Eggs are typically about 5 mm in diameter, slightly ovoid. They are opaque white, because of a calcareous layer in the shell. Juveniles often have lateral bands. Adult ''A. rufus'' and ''A. ater'' are straightforward to distinguish from ''A. vulgaris'' and ''A. flagellus'' by dissection; in the former pair the oviduct is thinner because the ligula is positioned in the upper atrium, not the oviduct. The anatomical differences between ''A. rufus'' and ''A. ater'' are more subtle: the latter tends to have a larger lower atrium, and its ligula differs (e.g. bowl-shaped rather than C-shaped). ''Arion rufus'' will often rock spectacularly from side to side when irritated, which is useful to distinguish it from ''A. flagellus'' and generally from ''A. vulgaris'', but not from ''A. ater''.


Taxonomy

Linnaeus Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his ennoblement in 1761 as Carl von Linné Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomial nomenclature, the ...
described ''A. rufus'' together with ''Arion ater'' in 1758. His description consisted mainly of references to earlier published descriptions from around Europe. Recently a
lectotype In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to anchor or centralizes the ...
for ''A. rufus'' has been designated from amongst the specimens to which Linnaeus indirectly referred. This is a non-surviving specimen amongst those that
Martin Lister Martin Lister FRS (12 April 1639 – 2 February 1712) was an English naturalist and physician. His daughters Anne and Susanna were two of his illustrators and engravers. J. D. Woodley, ‘Lister , Susanna (bap. 1670, d. 1738)’, Oxford Dic ...
described from
Almondbury Almondbury () is a village south-east of Huddersfield town centre in West Yorkshire, England. The population of Almondbury in 2001 was 7,368 increasing to 18,346 at the 2011 Census. Almondbury appears in the ''Domesday Book'' as "Almondeberi ...
in
West Yorkshire West Yorkshire is a metropolitan and ceremonial county in the Yorkshire and Humber Region of England. It is an inland and upland county having eastward-draining valleys while taking in the moors of the Pennines. West Yorkshire came into exi ...
, England. ''Arion rufus'' can be externally indistinguishable from ''Arion ater''. There are anatomical differences between the taxa in their genitalia, but they hybridise, and so they have often been considered conspecific, particularly by British authors. The appropriate name is then ''Arion ater rufus'' (i.e. a subspecies of ''A. ater''), following the decision of Fleming (" the first reviser", in 1822) to give ''A. ater'' precedence over ''A. rufus''. Differences in
mitochondrial DNA Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, such as adenosine triphosphate (ATP). Mitochondrial D ...
and minor anatomical differences exist between populations of ''A. rufus'' found in the British Isles and the commonest form found on the European continent. These have been given the status of species or subspecies. Because of the designation of the lectotype, the name ''rufus'' now refers to the British form, which may be called ''Arion rufus'', ''Arion rufus rufus'' or ''Arion ater rufus'' depending on which taxa are considered as species or subspecies. Garsault (1764) appears to have been the first to describe the Continental form under a name other than ''rufus'', so its name should be ''Arion ruber'', ''Arion rufus ruber'' or ''Arion ater ruber''. Quite possibly there are further forms of similar status from elsewhere in France and Spain.


Distribution

''Arion rufus'' is widespread in western Europe, including France, the Low Countries, Germany, western Poland, Switzerland and the southern parts of the British Isles. In Scandinavia and northern Britain the closely related species ''A. ater'' occurs in its place, but ''A. rufus'' has invaded parts of Scandinavia over the last 200 years. It is also extending its range further eastward in Europe, and even in eastern Germany it is possibly an old introduction. Its status in Spain is uncertain because of the presence there of other similar species. ''Arion rufus'' is also known as an introduction in North America. A related form, reddish in coloration but perhaps more closely related to ''A. ater'' s.s., has recently turned up in Turkey, on both sides of the
Bosphorus The Bosporus Strait (; grc, Βόσπορος ; tr, İstanbul Boğazı 'Istanbul strait', colloquially ''Boğaz'') or Bosphorus Strait is a natural strait and an internationally significant waterway located in Istanbul in northwestern Tu ...
.


Habitat

It is familiar from gardens and parks as well as disturbed agricultural landscapes, but also from a diversity of natural habitats including woodland, meadows, margins of water bodies, coastal habitat, and moorland. However, in much of its range ''A. rufus'' has declined dramatically over the last decades due to replacement by the externally similar ''Arion vulgaris''.


Life cycle

The species is adult in summer, although the timings vary by a month or so between localities. Typical would be for some individuals to reach adult size in May, but to mature only in July, with some surviving until October. The eggs hatch over a broad period from late autumn to spring and studies find great variation in growth rate. Adults are on average over 300 times the mass of hatchlings. The life cycle is predominantly annual; but possibly a few late hatchlings overwinter as juveniles and mature only 18 months or so after hatching.


Behavior

At rest ''A. rufus'' contracts into a hemispherical shape. When disturbed, it performs a rocking motion, sometimes for many minutes. Although predominantly nocturnal, rain brings it out during daylight. It is an
omnivore An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nu ...
. ''Arion rufus'' is hermaphrodite and during its mating
spermatophores A spermatophore or sperm ampulla is a capsule or mass containing spermatozoa created by males of various animal species, especially salamanders and arthropods, and transferred in entirety to the female's ovipore during reproduction. Spermatophores ...
are swapped reciprocally. Mating typically starts with one slug following the other, periodically nibbling its tail. When the leading slug doubles back, they may form a wheel configuration circling clockwise, with each nibbling the other. This soon evolves into the yin-yang configuration (or the wheel step may be skipped), with each animal hooked around the other, their genital pores pressed together, the configuration no longer rotating. The genitalia take some minutes to engage and evert, the
epiphallus The reproductive system of gastropods (slugs and snails) varies greatly from one group to another within this very large and diverse taxonomic class of animals. Their reproductive strategies also vary greatly, see Mating of gastropods. In many mar ...
(spermatophore producing organ) connecting to the bursa trunk of the other, mutually. This may take several attempts and sometimes is unsuccessful. Then the genital atria evert, and swell rapidly (1–2 min) to form a large, white, spherical mass between the bodies. The slugs remain like this for 90 minutes or longer, during which time a spermatophore is manufactured, filled with sperm, and in part passed over to the partner, hidden by the enveloping atria. Eventually one partner starts to become active, the configuration consequently rotates, the atria contract, and the genitalia separate. The spermatophores, anchored in the recipient's bursa trunk, are thereby pulled out of the donor's epiphallus. As the genitalia fully retract the spermatophore is taken in.


Gallery

Arion rufus 1650.JPG, Dark individual Red slug (Arion rufus).JPG, Light individual Arion rufus copulation, parende gewone wegslakken.jpg, Copulation Red Slug copulation.jpg, Mating


References


External links


''Arion rufus''
at
Encyclopedia of Life The ''Encyclopedia of Life'' (''EOL'') is a free, online encyclopedia intended to document all of the 1.9 million living species known to science. It is compiled from existing trusted databases curated by experts and with the assistance of ...
(3 pages)
''Arion rufus''
at
Animalbase AnimalBase is a project brought to life in 2004 and is maintained by the University of Göttingen, Germany. The goal of the AnimalBase project is to digitize early zoological literature, provide copyright-free open access to zoological works, and pr ...
taxonomy, short description, distribution, biology, status (threats), images {{Taxonbar, from=Q2153396 Arion (gastropod) Gastropods described in 1758 Gastropods of Europe Taxa named by Carl Linnaeus