Mucus feeder on microzooplankton and phytoplankton, near the surface down to circa 25m in the day, deeper after dawn.
Original taxon: Hyalaea gibbosa.
Synonyms: gibboides, hargeri.
Dredged at 800-1000m deep, Canale di Sicilia. 5mm.
The picture shows the inferior valve, with its typical concentric striations, at the top; and the superior one, which is radially folded (see below) at the bottom. Notice at right the hooked cuspis mediana, broken.
« Shell very globose, oval, as high as large, gibbous, anteriorly truncate, translucent, glossy; […] The bulbous part [of the inferior valve] almost smooth, becoming rippled in front, and covered, on the perpendiculary truncated part, with strong transverse spaced-apart costae, brace-shaped. […] Lateral spines obtuse, re-entrant; median spine, or posterior, short and strongly hooked. […] This is, in fact, the only [shell] to be so abruptly truncated in front of the inferior valve […] this is also the narrowest posteriorly, and the most gibbous of all those we have described. […] We fished this species since 1826, and describe it first; but we believe it is our duty to the name given by Mr. Rang etc. » – A. D. d’Orbigny: Voyage dans l’Amérique Méridionale vol. V, Paris 1835-1847.
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