Microstructure and formation of the calcareous operculum in Pyrgopolon ctenactis and Spirobranchus giganteus (Annelida, Serpulidae)

Abstract

The calcareous operculum of Pyrgopolon ctenactis is composed of spherulitic prismatic structures. The opercular cup consists of regular spherulitic prismatic crystals; the talon has two layers, an inner with an irregular spherulitic prismatic structure (150 lm thick) and an outer with a regular spherulitic prismatic structure (110 lm thick). The outer regular structure has thick (1 lm) organic interprismatic sheets unique in biomineralization of this group, but similar to that of Bivalvia. We infer that control over biomineralization is stronger during the formation of the outer regular layer, with its thick organic interprismatic sheets, than during the formation of the inner irregular spherulitic prismatic structure, without such sheets. In Spirobranchus giganteus, opercular formation differs from that of P. ctenactis. S. giganteus has numerous pores in its opercular plate, and calcification starts with the formation of an outer irregularly oriented prismatic structure followed by an oriented prismatic structure without interprismatic sheets.

Occurrence, Formation and Function of Organic Sheets in the Mineral Tube Structures of Serpulidae (Polychaeta, Annelida)

“…Serpulids can build tubes of aragonite, calcite or a mixture of both of these minerals [6], [4]. Serpulid skeletal microstructures are similar to those found in a variety of invertebrate phyla and are comparable to those of cnidarians and arthropods in diversity [8]. Serpulids form two major clades that have characteristic microstructural complexities.…”

On the unique isotropic aragonitic tube microstructure of some serpulids (Polychaeta, Annelida)

“…Spherulitic irregularly oriented prismatic structure is an isotropic structure and belongs among the ancestral serpulid tube structures (Vinn et al,2008a). It occurs in both major clades of Serpulidae (Vinn and Kupriyanova,2011).…”

“…However, serpulids possess a smaller number of skeletal microstructures than molluscs and bryozoans. Their diversity of skeletal structures is comparable to that of cnidarians and arthropods (Vinn and ten Hove,2011). There is one unique microstructure, hitherto described in Ditrupa Berkeley, 1835, termed regularly ridged prismatic structure by Vinn et al2008c.…”

“…The mineral composition of the aragonite‐dominated bimineralic calcareous tube produced by juvenile serpulids is strongly dependent on the aragonite saturation state (Chan et al,2012). In addition to the tubes, some serpulids secrete calcareous opercula (Vinn and ten Hove,2011). There are 14 skeletal microstructures hitherto known in serpulids (Vinn et al,2008a, c; Vinn and ten Hove,2011).…”

“…In addition to the tubes, some serpulids secrete calcareous opercula (Vinn and ten Hove,2011). There are 14 skeletal microstructures hitherto known in serpulids (Vinn et al,2008a, c; Vinn and ten Hove,2011). Serpulid skeletal microstructures are in general similar to those found in a variety of invertebrate phyla.…”