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Taxon profile

species

Plesiothyreus rushii (W.H. Dall, 1889)

kingdom Animalia - animals »  phylum Mollusca - mollusks »  class Gastropoda - gastropods »  family Phenacolepadidae »  genus Plesiothyreus

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Plesiothyreus rushii

Author: Dall, W.H.

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Description

Shell oval, translucent bluish white, almost perfectly flat, extremely thin. Nucleus of less than one whorl, half immersed, the remainder rising above the surface, smooth, not polished. Upper surface nearly flat, except near the nucleus which is situated nearly in the median line and close to the posterior margin ; concentrically faintly undulated ; with faint concentric growth lines, and with very numerous radiating lines of extremely minute slightly elevated points, recalling the granules of Poromya on a much finer and more minute scale. They are so small as to hardly appear elevated, but more like radiating lines of opaque dots on the generally translucent surface. Margin regularly ovate, entire, extremely thin. Under surface of shell mostly polished, a little domed under the part in front of the nucleus; there are faint markings (interrupted on the right side about the middle) which appear as if they might represent the area of muscular insertion, but the polish of the shell is such that this is not definitely ascertained. The sides of the shell are a little elevated, as if it had grown on a slightly concave surface, but the ends are depressed about to the same extent. Max. long. 9.3 mm.; max. lat. 7.5 mm.; posterior margin to nucleus, 1.8 mm.
DESCRIBED AS Umbraculum (Hyalopatina) rushii
Source: Dall, 1889. Reports on the results of dredgings, under the supervision of Alexander Agassiz, in the Gulf of Mexico (1877-78) and in the Caribbean Sea (1879-80), by the U. S. Coast Survey Steamer 'Blake,'. (Original description)

Interchangeable taxa

This remarkable shell has been some time in the National Museum and has been submitted to several conchologists, and studied with much care. In the absence of any further information, I have come to the conclusion that it may be related to Umbraculum, from which, conchologically, it is separated by its oval form, posterior nucleus, and granulated surface. The discovery of a living specimen, however, may show the true relations of the creature to be elsewhere. It has a little the general appearance of an extremely thin, flat Crepidula unguiformis without a deck, and with the nucleus within the margin.
Source: Dall, 1889. Reports on the results of dredgings, under the supervision of Alexander Agassiz, in the Gulf of Mexico (1877-78) and in the Caribbean Sea (1879-80), by the U. S. Coast Survey Steamer 'Blake'.

Distribution

Caribic. Bahama's.
Author: Jan Delsing

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