Milneria minima

Milneria minima
Milneria minima (holotype, from Dall, 1871: plate 16, fig. 5 and 6)
Systematics
Order : Carditida Superfamily : Carditoidea Family : Trapezoidal shells (Carditidae) Subfamily : Thecaliinae Genre : Milneria Type : Milneria minima
Scientific name
Milneria minima
( Dall , 1871)

Milneria minima is a shell - type from the family of trapeze shells (Carditidae). The species is already documented from the Pliocene .

features

The same-folding case is very small (up to 8 mm in length). It is approximately trapezoidal in outline and strongly unequal. The rear part of the housing is greatly elongated, so the vertebrae, which are rolled up perpendicular to the longitudinal axis of the housing , are located well in front of the center line. The posterior dorsal margin is long and straight, the anterior dorsal margin is straight to slightly concave, but only about half as long as the posterior dorsal margin. The rear edge is well arched. The ventral margin is concave in females and straight in males. The leading edge is very short. The lunula is wide, while the area is narrow and lanceolate. The ligament sits behind the vertebra. A lambda-shaped main tooth or two diverging main teeth are located in the left flap. In the right valve is a strong anterior main tooth and a slender posterior main tooth, which diverge from one another, as well as a very small anterior main tooth. There is also a shallow pit in the posterior dorsal margin that is missing in the left valve. Posterior teeth are absent with the exception of a very small posterior posterior tooth in the left valve.

The whitish skin is thick and firm. The ornamentation consists of four strong radial ribs in the rear part of the case, which are crossed by numerous, weaker ribs parallel to the edge. At the crossing points, the ribs parallel to the edge are scaled up. In the front part of the housing, faint radial stripes can appear, weaker than the ribs parallel to the edge. The inner edge of the case is notched. The periostracum is light brown.

Geographical distribution and habitat

The distribution area extends on the North American Pacific coast from Sartine Island (Scott Islands), northwest of Vancouver Island , British Columbia (50.8 ° N) to the south of Baja California (at 25 ° N).

The animals live in the deeper tidal range up to a depth of about 80 meters. They build byssus nests between stones or under larger bowls, or are firmly attached to a hard substrate with byssus threads.

Taxonomy

The species was first described in 1871 by William Healey Dall under the binomial Ceropsis minima . It is the type species of the simultaneously established subgenus Ceropsis Dall, 1871. However, this name is preoccupied and was replaced by Dall in 1881 by the name Milneria . The species is thus also the type species of Milneria Dall, 1881. The species is generally recognized as a valid taxon.

supporting documents

literature

• Eugene Victor Coan: Is there double trouble in marsupial clams. The Veliger, 17 (2): 183-184, 1972 online at www.biodiversitylibrary.org
• Eugene Victor Coan: Preliminary Review of the Northwest American Carditidae. The Veliger, 19 (4): 375–386, 1977 PDF (online at ResearchGate)
• Eugene Victor Coan, Paul Valentich-Scott: Bivalve Seashells of Tropical West America marine Bivalve mollusks from Baja California to Northern Perú. Part 1,598 pp., Santa Barbara Museum of Natural History, Santa Barbara 2012 ISBN 978-0-936494-43-2 (p. 385)
• Edouard Lamy: Review of the Carditacea vivants du Muséum National d'Histoire Naturelle de Paris. Journal de Conchyliologie, 66: 218–276, 289–368, Paris 1922 Online at www.biodiversitylibrary.org (p. 353)

Individual evidence

1. ^ ^{A b} William Healey Dall: Descriptions of sixty new forms of mollusks from the West coast of North America and the North Pacific Ocean, with notes on others already described. American Journal of Conchology, 7: 93-160, 1871. Online at www.biodiversitylibrary.org (p. 152) plate 16
2. ↑ William Healey Dall: Milneria, substitute name of Ceropsis Dall. The American Naturalist, 15: 718, 1881 Online at www.biodiversitylibrary.org .
3. ↑ MolluscaBase: Milneria minima (Dall, 1871)