The species has been dredged during the ‘Porcupine’ expedition of 1870, first in the south-west of the Celtic Sea (stations 3a & 6: 500fm & 358fm deep, at about 240nmi west of Brest, Brittany), second off Portugal (stations 16 & 17a: 994fm & 795fm deep, at about 27-30nmi in the north-west of Nazaré). The picture above shows the drawing of a left valve in Jeffreys: “On the Mollusca procured during the ‘Lightning’ and ‘Porcupine’ Expeditions, 1868-70. (Part III)”, Proceedings of the Zoological Society of London for the year 1881, plate LXI fig.2. Nota bene that it is not certain that tenera belongs actually to the genus Scacchia Philippi.
Here is the description given by the author, op. cit. p.696: « Shell oval, thin, rather convex, semitransparent, of a dull hue. Sculpture: numerous slight concentric striae, besides stronger and irregular hues of growth. Colour whitish. Epidermis filmy. Margins rounded on all sides, except at the back, where it is uneven… »
Above: a shell collected at 40-50m deep, in the Strait of Gibraltar. Size: 6,1mm.
« Beaks small, circular, projecting beyond the dorsal margin, slightly inclined to one side. Hinge-line nearly straight. Cartilage-pit small and narrow, placed obliquely under the beak… » – Same spot. 7,7mm.
« Inside polished. Scars imperceptible. »
Above: the right valve.
The shell of this species differs from that of S. zorni van Aartsen & Fehr-de Wal, 1985 « in being more rectangular in outline, in being inequilateral (the anterior side longer than the posterior one), as well as in having the outside smooth, i.e. without any trace of the divaricating radial sculpture present in S. zorni. As no left valve of “S.” tenera is known with certainty, we are not certain whether that species is correctly placed in the genus Scacchia. » – van Aartsen & Fehr-de Wal: “European marine Mollusca: notes on less well-known species. XI. Scacchia zorni spec. nov. (Bivalvia: Erycinidae) from the Atlantic coast of Portugal”, Basteria vol. 49, year 1985, p.67.
Compared to the mediterranean S. oblonga Philippi, 1836, Jeffreys’s figure of tenera is again much more rectangular in outline, and less inequilateral. Compared to the shell of S. maura van der Linden, 1996, tenera is less round in shape.
Regarding the shells pictured here, they seem to belong to specimens that are more adult than those collected by the ‘Porcupine’; despite this difference, it seems that their characteristics match those given by Jeffreys for his tenera.
Compared to the mediterranean S. oblonga Philippi, 1836, Jeffreys’s figure of tenera is again much more rectangular in outline, and less inequilateral. Compared to the shell of S. maura van der Linden, 1996, tenera is less round in shape.
Regarding the shells pictured here, they seem to belong to specimens that are more adult than those collected by the ‘Porcupine’; despite this difference, it seems that their characteristics match those given by Jeffreys for his tenera.