Paracratis minuta

Paracratis minuta
Paracratis minuta (original picture from Philippi 1836: plate 5 fig. 3a, b)
Systematics
Pteriomorphia Order : Arcida Superfamily : Limopsoidea Family : Limopsidae Genre : Paracratis Type : Paracratis minuta
Scientific name
Paracratis minuta
Philippi , 1836

Paracratis minuta is a shell - type from the family of Limopsidae in the order of Arcida .

features

The evenly folded, moderately expanded case has a maximum length of 12 mm. It is obliquely egg-shaped in outline, the rear part of the housing is elongated. It is also unequal and the vertebrae are in front of the midline of the case (and also in front of the middle of the dorsal margin). It is slightly higher than it is long; Nordsieck gives a ratio of length to height to thickness of 12: 13: 5 mm. The dorsal margin is short and straight. The longer posterior dorsal margin merges at a flat angle into the initially straight, then slightly arched posterior margin. The transition from the shorter anterior dorsal edge to the anterior edge is angled a little less flat, the corner can also be somewhat elongated in the shape of an ear. The front edge is well rounded. The rear edge and front edge merge into the comparatively tightly rounded ventral edge without any noticeable interruption. The dorsal field is narrowly deepened when viewed from above. The ligament is narrow-rhomboid and extends on both sides of the vertebra. The small triangular resilium sits in a shallow pit (resilifer) between the vertebrae. The taxodontic lock plate is wide; the upper edge is straight, the lower edge slightly bent at an angle; the kink is not in the middle of the lock edge, but behind the middle. The lock consists of two series of partly strong teeth, which are separated from each other by a toothless area. There are six small teeth on both sides, of which the three outer ones in the front area are quite large. The two sphincters are unequal in size. The posterior sphincter is about twice as large as the anterior sphincter and sits halfway up the rear edge. The front sphincter, on the other hand, is located just below the front end of the lock plate.

The aragonitic shell is thick and tightly skinned. The ornamentation consists of growth strips. The brown to straw yellow periostracum is drawn out into hairs or bristles, which, however, lie close to the surface. Especially at the edge they protrude like a fringe. The inner edge of the case is finely notched. In larger cases, however, the notch is limited to the rear ventral edge. The skin is usually light white, in older specimens it is also dirty white to light gray.

Geographical distribution, habitat and way of life

The distribution area extends in the eastern North Atlantic from Norway to Senegal and the Cape Verde Islands , in the western North Atlantic from Newfoundland to Florida , the Gulf of Mexico and Brazil . It is also found in the waters around the Canary Islands , the Azores in the western Mediterranean .

The animals are attached to stones, coral fragments and pebbles with a few byssus threads. They live in deeper water from the shelf edge to the middle shelf slope. Poppe and Goto give a depth distribution of 80 to 1353 meters water depth, Nordsieck from 55 to 1325 meters. The animals are suspension filter feeders.

Taxonomy

The taxon was first described by Rudolph Amandus Philippi in 1836 as Pectunculus minutus . Markus Huber proposed the new genus Paracratis for a group of species around Limopsis natalis Barnard, 1963, including Limopsis minuta , which MolluscaBase accepts as a valid taxon.

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. ↑ ^{a b} Rudolphus Amandus Philippi: Enumeratio molluscorum Siciliae cum viventium tum in tellure tertiaria fossilium, quae in itinere suo observavit. Vol. 1, pp. I-XIV (= 1-14), pp. 1–267, Berolini / Berlin, Schropp, 1836 Online at www.biodiversitylibrary.org (p. 63) plate 5 .
2. ^ ^{A b} Marine Bivalve Shells of the British Isles: Limopsis minuta (Philippi, 1836) (website of the National Museum Wales, Department of Natural Sciences, Cardiff)
3. ^ Eliézer de Carvalho Rios: Seashells of Brazil. 328 p., Fundação Cidade do Rio Grande, Fundação Universidade do Rio Grande, Museu Oceanográfico, 1985 (without ISBN) (p. 211)
4. ^ Markus Huber: Compendium of Bivalves. 901 S., Hackenheim, ConchBooks, 2010 ISBN 978-3-939767-28-2 (p. 587)
5. ↑ MolluscaBase: Paracratis minuta Philippi, 1836