Dark keel cone
| Dark keel cone | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Milax gagates | ||||||||||||
| ( Draparnaud , 1801) |
The dark keel snail ( Milax gagates ), also dark keel slug , is a nudibranch from the family of the keel snails (Milacidae) in the suborder of the land snails (Stylommatophora).
features
The body of the dark keel-snail reaches a length of 5 to 6 cm when stretched out. When preserved, the body shrinks considerably (25 to 30 mm long, 6 to 8 mm wide). Adult animals are mostly dark gray or black. There are also lighter color variants or slightly brownish shapes. The body color becomes lighter towards the sole of the foot. The coat takes up about 35-40% of the body length when stretched out. The keel is very clearly formed. and is trimmed at the rear end. The keel and the breathing opening are usually the same color as the body, the keel can sometimes be a little lighter or slightly brownish. There are 16 to 17 pits between the keel and the breathing opening. On the sides there are about 14 longitudinal rows with wrinkles on each side, each of which is colored a little more dull. However, the wrinkles are comparatively weak. The sole has darker edge zones in the longitudinal direction and a whitish middle zone, the sole slime colorless or whitish.
The short sperm duct (vas deferens) opens somewhat asymmetrically into the comparatively very thick epiphallus. The spermatic duct and epiphallus are about the same length. It is about twice as long as the penis and decreases significantly in thickness towards the transition to the penis. The penis is marked by a very large increase in thickness and the insertion of the penile retractor muscle at the transition area. The stimulator is highly conical, almost pointed at the end and a little bit laughed at the side. It is essentially smooth on the surface with a few papillae at the pointed end. The free fallopian tube (oviduct) and the vagina are very short. The sperm library has a very short, thick stem and an elongated, large, thick bladder. The atrium is short and somewhat narrowed compared to the vagina. The tufted accessory glands are long and tubular-thin and tangled in the lower part, and thickened in the distal part. They sit in the lower area of the vagina and open into it.
Similar species
The dark keel cone cannot be distinguished from the black keel cone ( Milax nigricans ) from the outside . A reliable determination can only be made by examining the genital tract. The stimulator of the black keel snail ( Milax nigricans ) has (significantly more) papillae at the base and not at the free end. Milax ater from North Africa has a stimulator without any papillae or has only a few extensions at the free end. On average, the black keel snail ( Milax nigricans ) is slightly larger, the coat is slightly smaller (in relation to the total length), the body is slightly lighter and the sole is monochrome.
Geographical distribution and habitat
The original distribution area was probably the western Mediterranean area including southern France and North Africa and perhaps the Canary Islands . Today the species is introduced almost worldwide, for example to Australia, South America, North America (e.g. Mexico, California), Tasmania, New Zealand, Japan, some Pacific islands (e.g. Hawaii, Rapa Nui , Juan Fernández Islands ) , South Africa, Sri Lanka and some Atlantic Islands (e.g. Bermuda , St. Helena ). In Europe, the species extends its range mainly to the north. It is firmly established in the coastal area of western France, Belgium and the Netherlands as well as the British Isles. According to Vollrath Wiese, the species occasionally occurs in cultivated land in Germany, but is not yet firmly established.
In the original distribution areas, the animals live in forests and bushland, natural meadows, preferably near water also near the coast. Otherwise, the dark keel snail occurs mainly in cultivated land due to the spreading with plants.
Way of life and reproduction
During the day, the animals hide under stones, under damp leaf litter and crevices or caves in the earth. They feed on fresh plant material and, when they multiply, can also be perceived as pests in the garden and vegetable growing, especially on root and tuber vegetables (e.g. carrots, potatoes).
In the British Isles, copulations take place from spring to autumn. The two partners are wrapped around each other very tightly so that the genitals are not turned outwards. Self-fertilization is possible. According to observations under laboratory conditions, the first eggs are laid 5 to 15 days after copulation. The eggs measure approximately 2 mm in length and 1.5 mm in diameter. Occasionally even larger eggs up to 3 mm occur. According to observations in France, the eggs are laid in October. A clutch contains up to 15 eggs, in total one individual can lay up to 100 eggs. The animals die 15 to 30 days after the last oviposition. The young hatch after 25 to 40 days with a length of 4 mm. Under natural conditions, sexual maturity is reached after 18 to 20 months. Under optimal laboratory conditions, sexual maturity can be reached after 4 to 5 months,
Taxonomy
The taxon was established in 1801 by Jacques Philippe Raymond Draparnaud . Limax gagates Draparnaud, 1801 is the type species of the genus Milax Gray, 1855. The genus and species are generally recognized. The species has often been confused with the black keel snail ( Milax nigricans ). The literature references on the geographical distribution of this species are therefore often unreliable. A reliable determination of the two types is only possible by examining the stimulator.
Danger
Since the dark keeled snail is not a native species in Germany, it is not rated in Germany's Red List.
literature
- Rosina Fechter and Gerhard Falkner: molluscs. Mosaik, Munich 1990, ISBN 3-570-03414-3 (= Steinbach's natural guide , volume 10), p. 184.
- Michael P. Kerney, RAD Cameron, Jürgen H. Jungbluth: The land snails of Northern and Central Europe. 384 pp., Paul Parey, Hamburg & Berlin 1983, ISBN 3-490-17918-8 , p. 179.
- Andrzej Wiktor: The slugs of the former Yugoslavia (Gastropoda terrestria nuda - Arionidae, Milacidae, Limacidae, Agriolimacidae). Annales Zoologici 46 (1-2): 1-110, Warsaw 1996
On-line
Individual evidence
- ↑ Francisco W. Welter-Schultes: European non-marine molluscs, a guide for species identification = identification book for European land and freshwater mollusks. A1-A3 S., 679 S., Q1-Q78 S., Göttingen, Planet Poster Ed., 2012 ISBN 3-933922-75-5 , ISBN 978-3-933922-75-5 (p. 439)
- ↑ Achuthan Nair, Fatma F. El-Toumi, Kama! MA Eltayeb, Abdelmuhsen Abusneina, Keshab Chandra Bhuyan: Habitat, occurrence & density of the pulmonate slugs in north-east Libya Journal of African Zoology, 110: 252-256, 1996
- ↑ a b c Rory J. Mc Donnell, Timothy D. Paine, Michael J. Gormally: Slugs: A Guide to the Invasive and Native Fauna of California. University of California Division of Agriculture and Natural Resources, Publication 8336, 2009 Preview at Google Books , p. 16.
- ↑ Kenneth A. Hayes: Invasive Land Snails of Hawaii. USDA, 2015 PDF
- ↑ PWDB Maheshini, KGDD Thilakarathne, GN Hirimuthugoda, KB Ranawana and S. Kumburegama: The distribution of terrestrial pest gastropods and their damage to agricultural crops in Kandy and Nuwara Eliya districts in Sri Lanka. Ceylon Journal of Science 48 (2): 177-184 2019 doi : 10.4038 / cjs.v48i2.7622 PDF (Research Gate)
- ↑ a b Vollrath Wiese: The land snails of Germany. 352 pp., Quelle & Meyer, Wiebelsheim 2014 ISBN 978-3-494-01551-4 (p. 201)
- ^ Jacques Philippe Raymond Draparnaud: Tableau des mollusques terrestres et fluviatiles de la France. Pp. 1-116. Montpellier, Paris, Renaud; Bossange, Masson & Besson, 1801. Online at www.biodiversitylibrary.org (p. 100)
- ↑ MolluscaBase: Milax gagates (Draparnaud, 1801)