Brackish trough clam

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Brackish trough clam
Brackish trough mussel (Rangia cuneata) (from GB Sowerby I, 1832: Plate 225 top and bottom illustration, combined [1])

Brackish water trough clam ( Rangia cuneata ) (from GB Sowerby I, 1832: Plate 225 upper and lower illustration, combined)

Systematics
Superordinate : Imparidentia
Order :
Superfamily : Mactroidea
Family : Trough clams (Mactridae)
Genre : Rangia
Type : Brackish trough clam
Scientific name
Rangia cuneata
( GB Sowerby I , 1832)
Brackish trough mussel ( Rangia cuneata ), inside (from GB Sowerby I, 1832: Plate 225 upper and lower illustration, combined)

The brackish water trough shell ( Rangia cuneata ) is a shell - type from the family of white clams (Mactridae). For Europe, it is an invasive type of brackish water, the occurrence of which was first detected in 2006 on the Belgian coast, and in 2016 also on the German North Sea coast. The original range are the coastal waters of the Gulf of Mexico .

features

The same-folding, inflated housing becomes fully grown 25 to 60 mm long, very rarely up to 85 mm. It is only slightly unequal. The prominently protruding, forward-curled vertebrae sit a little in front of the midline. The outline is oval-rounded triangular and slightly longer than high. The posterior dorsal margin is slightly arched, slopes steeply and merges into the posterior margin without noticeable interruption. The transition to the ventral margin is tightly rounded (narrower than the transition from the anterior margin to the ventral margin). The anterior dorsal margin is straight and also merges continuously into the anterior margin. The transition to the ventral margin is well rounded, as is the ventral margin. Internally, the dark brown ligament sits just below and behind the vertebra on a teardrop-shaped resilifer at a slight angle in the wide lock plate. Lunula and area are not developed. The lock plate is thick and wide with strongly developed teeth. Both valves have two main teeth, each forming a lambda-shaped projection. The very long posterior posterior tooth - it almost reaches the ventral margin - has a serrated upper side. That of the right valve with a pit corresponding to the main tooth and corresponding pits for the posterior teeth. There are two sphincters of almost the same size, which create clear scars in the shell. The surface line is indented short and rounded.

The whitish skin is thick, very firm and heavy. The ornamentation consists of strips parallel to the edge and weak wavy lines. The inner edge of the case is smooth. The olive to light brown periostracum does not peel off, wrinkled in some places. The inside is whitish-shiny.

Geographical distribution and habitat

The original range was probably the Gulf of Mexico . From there, the species has spread north along the North American east coast to the mouth of the Hudson River since 1955 . The first specimens were found in Belgium in 2005, in the Vistula estuary (Baltic Sea) in 2010, in 2013 in the Kiel Canal near Brunsbüttel and in the Baltic Sea on the Lithuanian coast, and in 2014 also in Estonia.

The species digs in estuarine , brackish, tidal habitats with a salinity of 5 to 15 PSU. Both tidal estuarine waters are populated as well as non-tidal marsh waters, which are separated from the direct access to the North Sea by a sluice and / or pumping station. The moderate influence of salt seems to determine the settlement here as well. Adults prefer soft soils made of mud or sand, overgrown by underwater vegetation and high water opacity. They feed on plant detritus and phytoplankton by filtering. It is possible that bacteria that sit on the plant detritus also make up a not inconsiderable part of the diet.

development

The animals are sexually separated. The sex products are released into the open water, where fertilization takes place. In the Gulf of Mexico, the brackish trough mussel has two spawning seasons, which, however, still differ somewhat regionally. In Louisiana, the spawning season begins in March and lasts through May, the second spawning season lasts from late summer to November. In Mexico a little further south, the first spawning season begins in February and lasts until June, the second spawning season from September to November. In these areas, gametogenesis was initiated by water temperatures above 15 ° C. The salt content had to be above 0 PSU, but could not exceed 15 PSU. The eggs measure 69 µm in diameter. Veliger larvae with a D-shaped larval housing develop from the fertilized eggs within 24 hours. These housings have a dorsal edge length of 55 to 60 µm. They grow to a length of 75 to 130 µm. They are a little longer than they are tall. The vertebra forms a little later. At this stage, the housing is 120 to 175 µm long. After seven days the metamorphosis began. The average life expectancy is four to five years. An example with a 75 mm case length should have been 10 years old.

Taxonomy

The taxon was first described in 1832 by George Brettingham Sowerby I as Gnathodon cuneatus . It is the type species of Gnathodon GB Sowerby I, 1832 by monotype . Gnathodon GB Sowerby I, 1832 was preoccupied by Gnathodon Oken, 1816 (fish). The type species of the genus Rangia Des Moulins, 1832 is Rangia cyrenoides Des Moulins, 1832, a synonym of Gnathodon cuneatus , so that this species is also a de facto type species of Rangia Des Moulins, 1832.

supporting documents

literature

  • Paul Chanley: Larval Development of the Brackish Water Mactrid Clam, Rangia cuneata. Chesapeake Science, 6 (4): 209-213, 1965, JSTOR 1350815
  • William Healey Dall: Monograph of the genus Gnathodon, Gray (Rangia, Desmoulins). Proceedings of the United States National Museum, 17: 89-106, Washington 1894 Online at www.biodiversitylibrary.org
  • Laurence D. Fairbanks: Biodemographic studies of the clam Rangia cuneata Gray. Tulane Studies in Zoology, 10: 3-47, 1963 Online at www.biodiversitylibrary.org
  • James D. Williams, Robert S. Butler, Gary L. Warren, Nathan A. Johnson: Freshwater Mussels of Florida. 525 pp., University of Alabama Press, Tuscaloosa 2014 ISBN 978-0-8173-8779-2 Preview on Google Books (p. 408)

On-line

Individual evidence

  1. ^ A b George Brettingham Sowerby I: The genera of recent and fossil shells, for the use of students in conchology and geology. Vol. 2, self-published, London 1820-34. P. 225 plate 40/218
  2. ↑ Beach Explorer: Brackish water trough clam ( Rangia cuneata )
  3. ↑ Annick Verween, Francis Kerckhof, Magda Vincx, Steven Degraer: First European record of the invasive brackish water clam Rangia cuneata (GB Sowerby I, 1831) (Mollusca: Bivalvia). Aquatic Invasions, 1 (4): 198-203, 2006 PDF
  4. ↑ meadow L., O. Niehus, Faass example, Meadow V .: Another occurrence of Rangia cuneata in Germany (Bivalvia: Mactridae). Writings on malacoology. 29: 53-60, 2016.
  5. ↑ LV RudinskayaA. A. Gusev: Invasion of the North American wedge clam Rangia cuneata (GB Sowerby I, 1831) (Bivalvia: Mactridae) in the Vistula Lagoon of the Baltic Sea. Russian Journal of Biological Invasions, 3 (3): 220-229, 2012 doi : 10.1134 / S2075111712030071
  6. ↑ Tiia Möller, Jonne Kotta: Rangia cuneata (GB Sowerby I, 1831) Continues its invasion in the Baltic Sea: the first record in Pärnu Bay, Estonia. BioInvasions Records, 6 (2): 167–172, 2017 doi : 10.3391 / bir.2017.6.2.13
  7. ^ US Fish and Wildlife Service Atlantic Rangia (Rangia cuneata) Ecological Risk Screening Summary Web Version –10/1/2012 PDF
  8. ↑ PDF
  9. ↑ a b MolluscaBase: Rangia cuneata (GB Sowerby I, 1832)