Angular ark shell

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Angular ark shell
Arca imbricata

Arca imbricata

Systematics
Order : Arcida
Superfamily : Arcoidea
Family : Ark clams (Arcidae)
Subfamily : Arcinae
Genre : Arca
Type : Angular ark shell
Scientific name
Arca imbricata
Bruguière , 1789

The angular ark mussel ( Arca imbricata ) is a type of mussel from the family of ark mussels (Arcidae).

features

The strongly bulbous housing is approximately rectangular in outline with a length of 2.5 to 4 cm. The length to thickness ratio of both flaps (L / D index) is 1.3. The rear part of the housing is clearly drawn out; Overall, the case is longer than it is high (L / W index = 1.5). The vertebra sits about a quarter (calculated from the total dorsal length) from the front end. The pointed, already beak-shaped vertebrae are very strongly curved and directed slightly backwards. The strong curvature of the vertebrae creates a broad dorsal surface when viewed from above.

The anterior dorsal margin merges more or less tightly rounded into the anterior margin. The front edge is almost straight or flatly arched and goes well rounded into the ventral edge. This is only slightly convex. A clear back ( carina ) runs from the vertebra to the angle between the posterior and ventral edge. The posterior dorsal margin falls off flat and goes moderately rounded into the posterior margin, and this closely rounded into the ventral margin. In the anterior region of the ventral margin the valves gape somewhat for the passage of the byssus. The inside of the ventral margin is smooth.

The edge of the lock is straight, the lock is taxodont, that is, it consists of many, small, approximately equal-sized teeth. The ligament extends the entire length of the dorsal margin, and also over a large part of the dorsal surface. It forms geometric patterns like triangles and rhombuses.

The skin is moderately thick and firm. The ornamentation consists of tightly standing, radial ribs, which are interrupted by growth stops and are knotty thickened. They usually become weaker towards the vertebra and can almost completely disappear. In the rear case field (from the carina to the dorsal edge) the few ribs are coarser, the field is drawn more brown. The periostracum is thick and shaggy. It is yellowish, light brown to dark brown and not very marked.

There are two sphincter muscles of unequal size; the anterior sphincter is slightly smaller than the posterior sphincter.

Similar species

The angular ark shell ( Arca imbricata ) has some resemblance to the Noah's ark shell ( Arca noae ). In this species, however, the vertebrae are twisted forward and the L / B index is somewhat larger, i.e. H. the case is significantly longer in relation to its height. The radial ribs of the angular ark shell, on the other hand, are finer and more numerous.

Geographical distribution and habitat

The distribution area of ​​the angular ark mussel extends from the Mediterranean Sea into the adjacent Atlantic Ocean and from the coasts of the Gulf of Mexico. It lives with byssus attached to rock under rock overhangs and in crevices.

The species occurs from just below the low water line to about 65 meters water depth.

Way of life

The animals are separate sexes and the sex products are released into the open water, where fertilization takes place. The diameter of the eggs is 74.1 ± 5.7 µm. From this a volume of 171.4 ± 27.3 µm³ can be calculated. A trochophora larva forms from this, which forms a first housing, the Prodissoconch I. The D-shaped Prodissoconch I has a width of 125.6 ± 6.7 µm.

The animals are occasionally attacked by the parasitic copepod Pseudomyicola spinosus , which anchors itself with two hooks in the mantle tissue and feeds on mucus that the mussel secretes to protect the mantle tissue. Constant loosening and re-anchoring can seriously damage the tissue of the infected animal, especially if not just one individual but several specimens of the parasite have settled in the mantle cavity.

Taxonomy

A first description of this species was written by Jean-Guillaume Bruguière in 1789. Fritz Nordsieck assigned the species in 1969 to his (new) genus Tetrarca Nordsieck, 1969, which, however , is regarded by the World Register of Marine Species as a synonym of Arca Linné, 1758.

Synonyms of the species are: Arca americana d'Orbigny, 1846, Arca martensii Dunker, 1868, Arca triundulata Bory de Saint-Vincent, 1827 and Arca umbonata Lamarck, 1819.

supporting documents

literature

  • Rosina Fechter, Gerhard Falkner: Mollusks. 287 p., Mosaik-Verlag, Munich 1990 (Steinbach's Nature Guide 10), ISBN 3-570-03414-3 (p. 76)
  • 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. 20 as Tetrarca imbricata )

Individual evidence

  1. ^ Amy L. Moran: Egg Size Evolution in Tropical American Arcid Bivalves: The Comparative Method and the Fossil Record. Evolution, 58 (12); 2718-2733, 2004, JSTOR 3449426
  2. ^ Arthur G. Humes: The cyclopoid copepod Pseudomyicola spinosus (Raffaele & Monticelli) from marine pelecypods, chiefly in Bermuda and the West Indies. Beaufortia, 14 (178): 203-226, 1969 PDF
  3. ^ Jean-Guillaume Bruguière: Encyclopédie méthodique. Histoire naturelle des vers. Tome premier. Paria, Panckoucke, 1789 Online at www.biodiversitylibrary.org (p. 98)
  4. ↑ World Register of Marine Species: Tetrarca Nordsieck, 1969
  5. ↑ a b World Register of Marine Species: Arca imbricata (Bruguière, 1789)

Web links

Commons : Arca imbricata  - collection of images, videos and audio files