Distribution and habitats of Acesta excavata (Bivalvia: Limidae) with new data on its shell ultrastructure

Abstract

Acesta excavata is the largest known bivalve associated with the Lophelia pertusa communities along the northeast Atlantic continental margin, but has also been found along steep cliffs, devoid of bathyal corals, and on more subdued topographies. During the Pleistocene, including the last glacial, A. excavata was widespread in the Mediterranean, but is in the Recent fauna known only from four Mediterranean sites. A new possible live-record from the Canyon du Var off Nice is presented. Radiocarbon dating (AMS 14C-method) on an A. excavata assemblage from the Strait of Sicily yielded a Late Pleistocene age of 39.9 ka. Biometric parameters indicate that Pleistocene Mediterranean shells achieved about the same maximum sizes as their Recent Atlantic counterparts, but individuals have been slightly smaller on average. The subspecies Acesta excavata sublaevis Nordsieck, based on a subfossil juvenile Mediterranean shell, is not considered a valid taxon. Mineralogical composition and ultrastructure of A. excavata have been analyzed using thin-sections, Feigel staining, x-ray diffractometry (XRD) and SEM-imaging. Its wide distribution, large size (15 cm) and simple shell architecture makes it a prime candidate for palaeoenvironmental studies in cold-water coral settings.