Mimachlamys varia nivea (Macgillivray, 1825)
MACGILLIVRAY, W. 1825. Description of a new species of Pecten from the Outer Hebrides. The Edinburgh Philosophical Journal, 13: 166-167 [p. 166, pl. 3, fig. 1]
1825 Pecten niveus Macgillivray, 1825
W. Macgillivray, 1825, plate 3.
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«IN a collection of shells transmitted to me from Harris, by a young man of that island, I found a beautiful species of Pecten, which, after a diligent search in various works on conchology, I consider myself authorised to pronounce non-descript. It occurs at the Island of Scalpay, and more abundantly at a place on the east coast of Harris, called Miavag-a-chuain. Its description is as follows:
Shell orbicular, in young specimens rotundato-oblong, subaequivalve, the upper valve, a little less convex than the under, thin, fragile, diaphanous, with 46 subcompressed, rounded ribs, sparsely echinated with transverse delicate laminae. Auricles very unequal: the longest of the upper valve with 7 divergent echinated ribs; and joined to the shell by a broad convex laminated rib; that of the lower vaIve broader, with 8 similarly echinated ribs; the smaller auricles also ribbed and echinated. Eight delicate marginal teeth on the upper valve close upon the auricle, and the series continued into the auricular groove. Interstices of the ribs marked with very fine transverse bent ridges and groove, scarcely visible to the unassisted eye. Colour pure white. The dimensions of the largest specimen which I possess are as follows: length 5 inches, breadth 2 1/1 1/2, length of auricular margin 1 1/4 inch. In respect to its general form and echinations, it approaches to P. varius, but it differs in the following particulars: P. varius is a thick opaque shell, with its transverse laminae coarse; this is a very thin diaphanous one, with the transverse laminae exceedingly delicate: in P. varius the ribs are 32, and marked with coarse irregular echinations; in this they are invariably 46 exceedingly delicate in themselves, and regular in their echinations; in P. varius the colour is various, sometimes yellowish white, yellow, brown, or mottled, or variegated, but never pure white; in this, it is white, so pure, that the inner surface has even a tint of blue. The differences in short are much greater than those between Venus pullastra, and decussata Cytherea exoleta and concentrica. I propose giving it the name of Pecten niveus, Snowy Scallop. In a systematic arrangement, it would rank under the division, Auricula altera majori, margine infra-auriculari denticulato; and might be characterized as follows: P. niveus orbicularis, fragilis, diaphanous, candidus, radiis 46, subcompressis, rotundatis, sparsim breviter tenuiterque echinatis. It is represented in plate III. Fig. 1» WILLIAM MACGILLIVRAY, 1825
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«In time it has been often a matter of dispute whether C. nivea is a distinct species, a subspecies, or just a form of C. varia. The fact that I have seen many specimens from the Irish Sea, Wales, and Scotland and never found intermediates between C. varia and C. nivea convinced me that we have to deal here with a distinct species, that by the special habitat required is confined to a limited area. Off the coast of Scotland at greater depths C. varia occurs.»
WAGNER, H. P. 1991. Review of the European Pectinidae (Mollusca: Bivalvia). Vita Marina, 41 (1): 1-48, pls. 1-7, text-figs. 1-25. [p. 28]
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Chlamys (Chlamys) nivea (MacGiIlivray, 1825); H. P. Wagner, 1991, Review of the European Pectinidae, plate 4, figure 4.
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«I fear that some of my conchological friends will be terribly shocked at my innovation in uniting P. niveus with P. varius; but I feel constrained to take this bold step, even at the risk of not being soon forgiven. I had for a long time great misgivings on the subject; but it was not until I had most carefully examined and compared a multitude of specimens of both these so-called species, collected from various and distant places, that I was able to arrive at a satisfactory conclusion. The only points of difference between P. varius and P. niveus consist in the latter having a broader and flatter shell with more numerous and delicate ribs, and in the colour being white. All these characters are combined or blended in specimens of P. varius and what I consider to be its two principal varieties. Some are broader and flatter than others: the number of ribs varies from 27 to 45, and consequently in their comparative fineness; and the white of P. niveus is sometimes beautifully tinted with purple, and passes into different shades of other colours. I have taken P. niveus only in every part of the Hebrides, and I have never seen a single specimen of P. varius from that district. In Loch Fyne and at Jura an intermediate variety occurs. A specimen from the former locality has 36 ribs, and one from the latter 32 ribs. I noticed in the collection of M. Martin, at Martigues, a white variety having also 32 ribs. A still more puzzling form was sent to me in 1852 by Mr. Barlee from GlengarifF in Bantry Bay, which clearly connects the two species; and the variety purpurea forms another link in the chain of specific identity. I believe this varietal difference arises from habitat. The strong and few-ribbed P. varius lives on oyster-banks and rough ground on an exposed coast; while the delicate and many-ribbed P. niveus is only found in sheltered lochs and arms of the sea, moored by
its strong byssus to the upper surface of the broad and smooth fronds of Laminariae.» JEFFREYS, J. G. 1864. British Conchology, or an account of the mollusca which now inhabit the British Isles and the sorrounding seas. Volume II. xiv, 465 p. pls. 1-8. John vanVoorst, Paternoster Row. London, 1863. [p. 56, 57]
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Mimachlamys varia nivea (Macgilvray, 1825); B. K. Raines & G. T. Poppe, 2006, A Conchological Iconography, The Family Pectinidae, pl. 231, figs. 4, 6, 7.
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