How did the carrier shell Xenophora crispa (König, 1825) build its shell? Evidence from the Recent and fossil record

Abstract

The genus Xenophora comprises species of marine gastropods (Cretaceous-Recent) able to add fragments of various origins to their shells surface. Agglutination potentials vary, from species lacking attachments to species completely covered by agglutinated materials, as in the Mediterranean species Xenophora crispa. Here, we analyse Recent and fossil specimens of Xenophora crispa from the Mediterranean area using SEM and XRD, to better understand their biomineralization patterns and the mechanisms leading to the agglutination of shells, bioclasts and lithoclasts, and their evolution in time. We also provide new data on poorly studied gastropod shell microstructures. We conclude that: a) most of the Xenophora crispa shell consists of an aragonitic crossed lamellar fabric, but fibrous to spherulitic prismatic fabrics, seemingly of calcite, have been found in the columella and peripheral edge (the thickest parts of the shell); b) the objects attachment is mediated by a prismatic microstructure, indicating that this may be the most functional fabric in attachment areas in molluscs; c) the functional purpose of the agglutination in Xenophora crispa may be related to a snowshoe strategy to successfully colonize muddy substrates, coupled with tactile and olfactory camouflage. Indeed, this species secretes in the columella and peripheral edge a less dense and a more organic rich calcitic fabric, possibly to lighten the shell thickest parts in order not to sink in soft sediments and to facilitate the shell raising from the substrate to create a protected feeding area. This behaviour seems to have been maintained by X. crispa over 2 My time span.

Palaeoclimatic and palaeoenvironmental evolution of the Lower Pleistocene Arda River succession

“…However, it is important to check for any sign of possible diagenetic overprint that may alter the shell isotope composition. One of the most used and easily available screening method is the analysis of the shell microstructure at the Scanning Electron Microscope (e.g., Angiolini et al, 2009;Crippa, 2013;Crippa et al, 2016a, b;Ye et al, 2018;Crippa et al, 2020). Based on this premise, a sclerochemical analysis was performed on a pristine specimen of Glycymeris inflata (Fig.…”