Arca (genus)

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Arca
Noah's ark shell (Arca noae)

Noah's ark shell ( Arca noae )

Systematics
Subclass : Pteriomorphia
Order : Arcida
Superfamily : Arcoidea
Family : Ark clams (Arcidae)
Subfamily : Arcinae
Genre : Arca
Scientific name
Arca
Linnaeus , 1758

Arca is a shell - genus from the family of ark shells (Arcidae); it is the type genus of the family or subfamily Arcidae or Arcinae.

features

The same-flap, mostly bulbous cases are medium to large in size and reach a maximum length of about ten centimeters. They are approximately trapezoidal to rectangular, with some species the greatest width is reached in the rear part of the housing. They are always significantly longer than high (mostly L / H index> 1.5 to over 2). The broad vertebrae are widely spaced and curved forward. They lie in front of the middle of the dorsal margin, i.e. H. the casing is always more or less clearly longer behind the vertebra than in front of the vertebra. There is always a byssus ; The passage for the byssus is located roughly in the middle of the ventral margin. At this point the flaps gape even when the housing is closed. A more or less clearly pronounced ridge (carina) runs from the vertebrae to the transition from the rear to the ventral edge. The rear edge is often more or less clearly indented. The ventral margin is not serrated. However, the housings are often quite variable within a species.

The lock edge is long, straight or slightly kinked or curved with many similar teeth. The teeth are vertical or oblique to almost parallel to the edge of the lock. Between the vertebrae lies the broad ligament field with rhombic patterns and often also with a fluting.

The ornamentation consists of strong radial and concentric ribs that can form a grid pattern. Many Arca species are colored with vivid patterns. Many species have simple eyes on the edge of the mantle.

Similar genera

The shells of the Barbatia species are usually somewhat smaller and rather oblong-egg-shaped. They are mostly flat, i.e. H. not particularly bloated. The dorsal margin does not extend over the entire length of the housing. On the rear part of the case, a keel from the vertebra to the rear edge is missing or only a weak keel is formed. The Acar genus , on the other hand, has housings that do not or only slightly gape at the ventral edge. The ridge from the vertebra to the rear edge is also usually not very pronounced.

Geographical distribution and habitat

The species of the genus inhabit warm and tropical seas worldwide, only a few species are also found in temperate latitudes. They are predominantly inhabitants of the shallower water from the tidal range to about 100 meters water depth. Only a few species penetrate to greater depths.

The species of the genus Arca are mostly hard-soil dwellers who attach themselves to hard substrate with byssus threads.

Taxonomy

The genre was established by Carl von Linné as early as 1758 . Type species is the Noah's ark shell ( Arca noae ) by later determination. The MolluscaBase currently assigns 28 species to the genus Arca . There are also a large number of fossil species that have not yet been fully recorded.

The Paleobiology Database lists more than 80 (other) fossil species, which, however, meanwhile e.g. T. have already been assigned to other genera. The difficulty in naming a reliable number of species is that the genus Arca used to be much broader, but is now divided into several smaller genera. Many species remained in the genus Arca without revision , but could probably be included in one of the Arca s. st. separated genera are classified.

The MolluscaBase treats the following genera as synonyms : Byssoarca Swainson, 1833, Cibota Mörch, 1853, Daphnoderma Poli, 1795, Navicula Blainville, 1825 and Tetrarca F. Nordsieck, 1969.

Huber (2010) eliminates a total of four groups within the genus Arca , which he does not separate in terms of formal nomenclature; there are Arca (Arca) = Arca s. st. or the noae group, Arca (Tetrarca) Nordsieck, 1969 or the tetragona group (with Arca tetragona Poli, 1795, Arca acuminata Krauss, 1848 and Arca ocellata Reeve, 1844), the so-called avellana group with Arca patriarchalis Röding, 1798 (= avellana Lamarck, 1819), Arca imbricata Bruguière, 1789, Arca mutabilis (GB Sowerby I, 1833), Arca turbatrix Oliver & Cosel, 1993, Arca ventricosa Lamarck, 1819 and Arca volucris Reeve, 1844, and a fourth group, which is characterized by Arca boucardi Jousseaume, 1894.

supporting documents

literature

  • Rudolf Kilias: Lexicon marine mussels and snails. 2nd edition, 340 p., Verlag Eugen Ulmer, Stuttgart 1997 ISBN 3-8001-7332-8 (p. 25)
  • Raymond Cecil Moore (Ed.): Treatise on invertebrate paleontology. Mollusca, 6, Bivalvia 1. XXXVIII, 489 pp., New York, 1969 (pp. N250 / N252).
  • 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. 19)

Individual evidence

  1. ^ Carl von Linné: Systema naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata. Pp. 1–824, Holmiae / Stockholm, Salvius, 1758. Online at Göttinger Digitization Center (p. 693).
  2. ↑ a b c MolluscaBase: Arca Linnaeus, 1758
  3. ^ Philip W. Reinhart: Mesozoic and Cenozoic Arcidae from the Pacific Slope of North America. Geological Society of America Special Papers, 47: XI + 117 S., 1943 limited preview at Google Books
  4. ^ Paleobiology Database: Arca Linnaeus 1758
  5. ^ Markus Huber: Compendium of bivalves. 901 S., Hackenheim, ConchBooks, 2010 ISBN 978-3-939767-28-2