Conical marsh snail
| Conical marsh snail | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Assiminea grayana |
||||||||||||
| Systematics | ||||||||||||
|
||||||||||||
| Scientific name | ||||||||||||
| Assiminea grayana | ||||||||||||
| Fleming , 1828 |
The conical marsh snail ( Assiminea grayana ), also known as the marsh snail. is a worm art from the family of assimineidae that the Caenogastropoda is expected,
features
The right-hand wound, highly conical, apically pointed shells are 4 to 6 mm (4 to 5 mm) high and 2.5 to 3 mm wide. The last turn takes up about 70-75% of the total height, the mouth about 40-45% of the total height. The apical angle is 59.5 ± 5.6 °. The height-width index and thus also the apical angle is somewhat variable. The case has six to seven, only slightly arched, very regularly increasing turns, which are separated from each other by a shallow seam and. The periphery appears almost straight. The shell is translucent and comparatively very firm. The matt, glossy surface of the case has fine, somewhat irregular growth stripes that are slightly inclined in relation to the spindle axis. Weaker spiral lines occur especially on the older turns. A spiral line under the suture is usually more pronounced. The mouth is generally egg-shaped, slightly angled on the periphery. The mouth rim is only thickened in the spindle area, otherwise hardly thickened or turned over. The housing color ranges from yellowish horn-colored to brownish. Occasionally there is an indistinct red-brown band on the last lap on the periphery or a little below the periphery. There is no navel, at most a slight pit. The protoconch or the embryonic housing consists of a total of two turns with a diameter of 350 μm. There are 12 spiral lines on the larval case.
The separate-sex animals have a broad, trunk-like and bilobed snout. The sides are drawn out like a keel. Below these keel-like structures, ciliated pits run from the mantle cavity down the sides of the foot. The edge of the coat is simple, with no coat tentacles. The foot is shield-shaped, almost straight at the front end, the rear end rounded. The eyes sit on small hill-like structures at the apex of the very short head tentacles. The gill has receded. The case can be closed by a spiral, dark to almost black operculum. The soft body is gray with purple stripes. The head is much darker than the rest of the soft body. The tips of the tentacles are not pigmented. The side of the foot are white or off-white. The sole is light gray with lighter spots. The gill is reduced and replaced by two cilia-covered bulges for breathing; one bead is at the base of the mantle cavity, the second bead is at the top of the mantle cavity. Often an air bubble is held in the mantle cavity. In contrast, the osphradium was preserved.
The males are on average slightly smaller than the females. The males have a long penis (0.5 × 3 mm long when erect) that attaches to the center of the back behind the bases of the tentacles in the mantle cavity. In females, the genital opening is on the right side.
The radula has seven elements per half transverse row. The middle plate is almost square with rounded front corners and a bent five-toothed edge. The middle tooth is larger than the rest, all five teeth are rounded. The three basal teeth are one behind the other. The intermediate plate is rounded, longer than wide, with an edge bent forward. This has five sharp teeth. The plate has a lamellar extension on the outside. The inner side plate is narrower than the intermediate plate (and the outer side plate). The edge is strongly bent and has four sharp teeth. The outer side plate is relatively very wide and becomes a bit narrower towards the base. At the top it has eight small, pointed teeth. The radula has about 58 transverse rows.
Similar species
The conical marsh snail differs from the hydrobes that occur in the same habitat by its less highly conical shell, i.e. the lower height-width index.
Geographical distribution and habitat
The conical marsh snail occurs on the coast from Denmark to France and northwestern Spain as well as on the east coast of England. The occurrences on the west coast of Ireland may result from anthropogenic displacement.
The habitat of the species are salt marshes and outer dike meadows above the mean high tide.
Way of life
The animals live on salt marshes and outer dyke meadows above the mean high tide, but also in brackish pools near the coast, where they crawl around on the damp mud. They also like to hide under (isolated) stones or driftwood in this habitat. They tolerate large fluctuations in salinity from euhalin to fresh water.
They feed on dead, but also fresh, plant material, whereby they probably graze on diatoms and other microorganisms that grow on them than the plants themselves. The fecal pills are egg-shaped with a diameter of 450 × 90 μm. They contain detritus and diatom frustules.
The sexes are separate. The mating season begins in April. When mating, the male sits down on the right front edge of the housing of the female, which continues to crawl around. The male now inserts the penis into the female's sexual opening and transfers the sperm. The female produces up to 80 eggs per clutch. They slide individually down the right longitudinal pit and are grouped into clutches on the mud in the animal habitat, e.g. T. with the help of the foot and snout. The clutches measure about 5 × 1 mm. The colorless eggs measure 150–200 × 200–250 μm. Each egg is enclosed separately in a double-shell capsule. The inner layer is completely transparent, while the outer layer is less clear, often containing fibrous elements, and the outer side is stuck together with silt particles. The clutch is covered with a layer of muddy fecal pills. The eggs are thus well protected against dehydration and also well camouflaged against predators.
Embryonic development takes four to five days at around 20 °. Then the Veliger larva is ready to hatch and moves in its shell. By this point in time, it has already formed a first housing comprising just under one turn. However, for further development it must come into the open sea. The larvae in the clutches now have to wait for the next flooding of the salt marshes. If the clutch is now submerged in the salt marshes, the outer shell tears first. The inner shell swells up to 16 times its volume. Then this shell bursts explosively, breaks through the layer of fecal pills and hurls the Veliger larvae into the water. After two months of waiting under the manure cover, all larvae were ready to hatch. After 3.5 months there were still just under around two thirds of the larvae. After five months the proportion of still living larvae had sunk to 13%, after almost six months all larvae were dead. However, the period in which the larvae remain capable of hatching is also temperature-dependent. In a clutch kept at 5 ° in the laboratory, some larvae were still able to hatch even after nine months. The salt content also affects the hatchability; If the salt content is above the salt concentration of the North Sea (28 ‰), the hatchability decreases with increasing salt content of the water. It is not known how long the larva will live in free water before switching to soil life and initiating metamorphosis. The growth and age structure of the populations are also unknown, but they probably only live to be one year old.
Taxonomy
The taxon was first described by John Fleming in 1828. It is the type species of the genus Assiminea by monotype. The species name is named after JEG Gray (1800–1875) curator for zoology at the British Museum (Natural History). The genus and species are generally recognized today.
Danger
The conical marsh snail is threatened with extinction in Germany. However, according to the assessment of the International Union for Conservation of Nature and Natural Resources (IUCN), it is not endangered overall.
supporting documents
literature
- Vera Fretter, Alastair Graham: The prosobranch molluscs of Britain and Denmark. 3. Neritacea, viviparacea, valvatacea, terrestrial and freshwater littorinacea and rissoacea. The Journal of Molluscan Studies: Supplement; 5: 101-140, London 1978.
- 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., Planet Poster Ed., Göttingen 2012, ISBN 3-933922-75-5 , ISBN 978-3-933922-75-5 (**)
- Vollrath Wiese: Germany's land snails. 352 pp., Quelle & Meyer, Wiebelsheim 2014 ISBN 978-3-494-01551-4 (p. 35)
Individual evidence
- ↑ Jürgen H. Jungbluth, Dietrich von Knorre: Trivial names of land and fresh water mollusks in Germany (Gastropoda et Bivalvia). Mollusca, 26 (1): 105-156, Dresden 2008 ISSN 1864-5127
- ↑ a b Wiese, Landschnecken, p. 35
- ↑ Welter Schultes in AnimalBase: Assiminea grayana Fleming, 1828
- ↑ Franz Hermann Troschel: The teeth of snails to justify a natural classification. Volume 1. Nicolaische Verlagsbuchhandlung, Berlin, 1856-63 Online at Google Books ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. (P. 105)
- ↑ L. Bruydoncx, K. Jordaens, H. de Wolf, P. Meire, T. Backelau: New records of Assiminea grayana Fleming, 1828, Myosotella myosotis (Draparnaud, 1801) and Pisidium subtruncatum Malm, 1855 (Mollusca: Gastropoda, Bivalvia ) in the Scheldt estuary. Bulletin de l'Institut Royal des Sciences Naturelles de Belgique, Biology, 70: 103-106, Brussels 2000 PDF
- ↑ John Fleming: A history of British animals, exhibiting the descriptive characters and systematic arrangement of the genera and species of quadrupeds, birds, reptiles, fishes, Mollusca, and Radiata of the United Kingdom; including the indigenous, extirpated, and extinct kinds, together with periodical and occasional visitants. I-XXXII, 1-565, Bell & Bradfute, Edinburgh, 1828 Online at www.biodiversitylibrary.org (p. 275).
- ↑ Fauna Europaea: Assiminea (Assiminea) grayana Fleming 1828
- ↑ JH Jungbluth, D. von Knorre (with the assistance of U. von Bössneck, K. Groh, E. Hackenberg, H. Kobialka, G. Körnig, H. Menzel-Harloff, H.-J. Niederhöfer, S. Petrick, K Schniebs, V. Wiese, W. Wimmer, ML Zettler): Red list of internal mollusks [snails (Gastropoda) and mussels (Bivalvia)] in Germany. Announcements of the German Malacoological Society, 81: 1–28, Frankfurt / M. 2009 PDF ( Memento of the original from June 16, 2013 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. (1.3 MB)
- ↑ Assiminea grayana in the endangered Red List species the IUCN 2013. Posted by: Killeen, I. & Seddon, MB, 2010. Retrieved on June 12, 2014.
