Propeamussium lucidum (Jeffreys in Thomson, 1873)
THOMSON, W. 1873. The depths of the sea. An account of the general results of the dredging crises of H. M. SS. "Porcupine" and "Lightning" during the summers of 1868, 1869, and 1870, […]. MacMillan and Co. London. [p. 464, figs. 78a, 78b]
1873 Pleuronectia lucida Jeffreys in Thomson, 1873
1879 Amussium [sic] lucidum var. striata Jeffreys, 1879
1897 Amussium [sic] hypomeces Dautzenberg & Fisher, 1897
1898 Propeamussium editae Gregorio, 1898
1989 Propeamussium centobi Schein, 1989
1879 Amussium [sic] lucidum var. striata Jeffreys, 1879
1897 Amussium [sic] hypomeces Dautzenberg & Fisher, 1897
1898 Propeamussium editae Gregorio, 1898
1989 Propeamussium centobi Schein, 1989
W. Thomson, 1873, figure 78.
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«Pleuronectia lucida, JEFFREYS (Fig. 78), a pretty little clam belonging to the Pecten pleuronectes set, is figured both from the North Atlantic and from the Gulf of Mexico. The abyssal mollusca are by no means devoid of colour, though, as a rule, they are paler than
those from shallow water.» JOHN GWYN JEFFREYS, 1873
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«Type locality
Off the British Isles, 1019 m depth. For additional data see Warén (1980: 43). Distribution
Northern to tropical eastern Atlantic (64°N–15°N), south of Greenland, southwest of Iceland and south of the GreenlandScotland Ridge. Bathymetric range from ca. 785 m (Dijkstra & Goud 2002) to 4453 m (Morton & Thurston 1989). BIOICE material alive at four stations in 1042–1327 m (Map 2). Description
Shell (Figures 1A,B, 3E,F) up to ca. 15 mm high, fragile, usually transparent, rarely opaque, slightly higher than long, left valve slightly more convex than right valve, equilateral (anterior and posterior end of disc of similar shape); anterior auricles larger than posterior ones. Prodissoconch (Figures 2F), length ca. 200–230 μm, white. Left valve almost smooth, sometimes irregularly sculptured with weak radial and/or commarginal striae or delicate lirae (Figures 4I, 8I). Right valve with regularly spaced, commarginal lirae (Figures 4J, 8J). Anterior auricle dorsally spiny. Internal radial ribs generally 9, rarely 8 or 10, with a few rudimentary interstitial and 2 auricular ones. Byssal notch small, ctenolium (series of teeth along the edge of the shell, close to the anterior ears) lacking. Remarks
Propeamussium lucidum seems to be scarce off Iceland (Ockelmann 1959), but rather common in the temperate and subtropical regions of the eastern Atlantic (Salas 1996; Dijkstra & Goud 2002; Dijkstra & Gofas 2004). Its supposed occurrence in the western Atlantic seems to be based on Jeffrey’s old record (see below). The BIOICE specimens are very similar to the type material. Propeamussium lucidum varies in sculpture on the left valve, usually very weak radial striae, sometimes with a few radial ribs anteriorly and posteriorly. A weak reticulated sculpture is formed when both radial and commarginal striae are developed. Specimens from the temperate East Atlantic are nearly smooth (as in the types), whereas more southern specimens are weakly sculptured (P. hypomeces morphs: weak commarginal sculpture, and P. centobi morphs with weak radial sculpture or weak reticulate sculpture; based on examination of specimens in BMNH, MNHN, NNM). For discussion of geographical morphs see Dijkstra & Goud (2002) and Dijkstra & Gofas (2004). Jeffreys’ (Thomson 1873:465) figures of Pleuronectia lucida belong to two species: the North Atlantic P. lucidum (Figure 78a, lv), and Propeamussium pourtalesianum (Dall, 1886) from the Gulf of Mexico (Figure 78b, rv). A more precise locality ‘Gulf of Mexico, off Alligator Bank, 156 fms’ of the latter specimen was given by Jeffreys (1876:425) and the identification by Jeffreys (in Thomson 1873) was followed by Dall (1881:117), but in 1886 Dall introduced a new species name Amusium (Propeamussium) pourtalesianum for Jeffreys’ ‘Pleuronectia lucida’ from the western Atlantic. Propeamussium pourtalesianum differs from P. lucidum by having a more circular disc (P. lucidum is elongate), 10 instead of 9 internal ribs and a coloured left valve instead of a colourless or transparent one. Several variations were described by Jeffreys (1879:562) and Locard (1898:407), but they are individual and geographic. Amussium lucidum var. striata Jeffreys, 1879 was based on specimens of the same appearance as P. centobi with ‘distinct longitudinal striae’. We consider it a synonym of P. lucidum. Schein (1989) gave a length of 170 μm for prodissoconch 2, but both our measurements (ca. 220 μm) and those in Morton & Thurston (1989:476), 200-230 μm, differ considerably. It is obvious that Schein’s figure 11 is strongly tilted and this may explain the discrepancy.» DIJKSTRA, H. H., A. WARÉN & G. GUDMUNDSSON. 2009. Pectinoidea (Mollusca: Bivalvia) from Iceland. Marine Biology Research, 5: 207-243, figs. 1-20. [p. 210, 211, 213, 214]
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Propeamussium lucidum (Jeffreys in Thomson, 1873); H. H. Dijkstra, A. Warén & G. Gudmundsson, 2009, Pectinoidea (Mollusca: Bivalvia) from Iceland, figures 1A, 1B, 3E, 3F.
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