Limopsis aurita

Limopsis aurita
Limopsis aurita (from Bronn, 1838, plate 39, fig. 7)
Systematics
Pteriomorphia Order : Arcida Superfamily : Limopsoidea Family : Limopsidae Genre : Limopsis Type : Limopsis aurita
Scientific name
Limopsis aurita
( Brocchi , 1814)

Limopsis aurita (Brocchi, 1814) (original illustration from Brocchi, 1814, plate 11, fig. 9a, b)

Limopsis aurita is a shell - type from the family of Limopsidae in the order of Arcida .

features

The equally flattened, strongly flattened housing has a maximum length of 20 mm. Juvenile cases up to 2 mm in diameter are almost round in outline, with increasing age they become more oblique-ovoid. Juvenile housings are about as high as long or slightly higher than long (ratio length: height: thickness 10: 11: 4 mm, north triangle). With increasing size, the rear part of the housing is lengthened to a greater or lesser extent, it becomes more and more oblique-egg-shaped or oblique-elliptical. Fritz Nordsieck gives a ratio of length to height to thickness of 36: 22: 9 mm (subspecies transversa ).

The small vertebrae therefore sit in front of the center line of the housing. They are not particularly protruding, pointed and curled forward, and the dorsal field between the vertebrae is deeply incised.

The short dorsal margin is straight, the rear and front dorsal margin are roughly the same length. The posterior dorsal margin merges into the very flat arched posterior margin at a very flat angle. Occasionally these transitions are a little more emphasized ( ears ), hence the name. The anterior dorsal margin also merges into the well-rounded anterior margin at a very flat angle. The ventral margin is well rounded.

The ligament is external and extends in front of and behind the vertebra. The small, triangular resilium lies in a shallow pit between the vertebrae. The upper edge of the lock plate is straight, the lower edge is arched or slightly angled. The kink of the angle is not exactly below the vertebrae, but clearly behind the vertebrae. The taxodonte lock consists of two series of strong teeth, which are not arranged in a mirror image. In the front series there are up to eight teeth, in the back series up to nine teeth, which are separated from each other by a narrow toothless area. The two sphincters are unequal in size, the anterior sphincter is only about half the size. The posterior sphincter is about halfway up the posterior rim, the anterior one below the transition between the dorsal rim and the posterior rim. The surface line is not indented.

The aragonitic shell is thick and tightly skinned. The ornamentation consists of concentric fine ribs that are crossed by fine radial lines. The inner edge of the case is smooth. The periostracum is straw-yellow to reddish and drawn out into fine hairs, which, however, are often only preserved at the edge of the case and protrude like fringes there. The periostracal hairs lie close to the surface and are arranged in lines that correspond to the fine radial lines of the shell surface. The shell of juvenile specimens is glossy white, older shells are often gray.

The soft body is cream-colored. The foot is long and worm-shaped; it is stretched out longer than the case. The gills are filibranch.

Geographical distribution, habitat and way of life

The distribution area of ​​the species extends from Norway (including the northern North Sea ) to the Mediterranean (after Poppe and Goto to Senegal ). Isolated occurrences are known from the Canary Islands , the Azores , Iceland and from Newfoundland , Bermuda and the Virgin Islands . It prefers somewhat deeper water, usually from the shelf edge to the upper shelf slope (about 200 to 600 meters water depth). However, they also occur in shallower water (up to 20 m) and in significantly deeper areas (up to 4,400 meters).

The animals are found on a wide range of different soils, from muddy to gravelly soils. They live half-buried in the sediment and anchor themselves to a larger particle or stone with a single thread of byssus. They usually stay in one place for a long time, but can then move over a short distance and anchor again there. The animals are suspension filter feeders that feed mainly on planktonic microorganisms, as gastric contents have shown.

development

The animals are of separate sex. The orange-red eggs have a diameter of 140 µm, so they are comparatively very large. The largest specimens produce around 6,000 eggs, which, like sperm, are released into the open water and fertilized there.

Taxonomy

Giovanni Battista Brocchi was the first to describe this species in 1814. It is the type species of the genus Limopsis Sassi, 1827.

Fritz Nordsieck distinguishes three subspecies: Limopsis aurita aurita with nine varieties, Limopsis aurita transversa Locard, 1897 and Limopsis aurita pelagica (Philippi, 1836).

literature

• Fritz Nordsieck : The European sea shells (Bivalvia). From the Arctic Ocean to Cape Verde, the Mediterranean Sea and the Black Sea. 256 p., Gustav Fischer Verlag, Stuttgart 1969 (p. 27)
• Graham Oliver, John A. Allen: The Functional and Adaptive Morphology of the Deep-Sea Species of the Family Limopsidae (Bivalvia: Arcoida) from the Atlantic. Philosophical Transactions of the Royal Society of London Series B. 291: 77-125, 1980 JSTOR .
• Guido Poppe and Yoshihiro Goto: European Seashells Volume 2 (Scaphopoda, Bivalvia, Cephalopoda) . 221 pp., Verlag Christa Hemmen, Wiesbaden 1993 (2000 unc. Reprint), ISBN 3925919104 (p. 45)

Individual evidence

1. ^ Heinrich Georg Bronn: Lethaea geognostica or illustrations and descriptions of the most characteristic fossils for the mountain formations. Volume 2. pp. 769-1346, Stuttgart, Schweizerbart's Verlagshandlung, 1838 ( p. 935 and plate 39 ).
2. ^ ^{A b} Giovanni Battista Brocchi: Conchiologia fossile subappenninica con osservazioni geologiche sugli Appennini e sul suolo adiacente. 2 volumes, 712 pages, Milan, 1814.
3. ^ ^{A b} Marine Bivalve Shells of the British Isles: Limopsis aurita (Brocchi, 1814) (website of the National Museum Wales, Department of Natural Sciences, Cardiff)
4. ↑ MolluscaBase: Limopsis aurita (Brocchi, 1814)