The architecture of Recent brachiopod shells: diversity of biocrystal and biopolymer assemblages in rhynchonellide, terebratulide, thecideide and craniide shells

Abstract

Biological hard tissues are a rich source of design concepts for the generation of advanced materials. They represent the most important library of information on the evolution of life and its environmental conditions. Organisms produce soft and hard tissues in a bottom-up process, a construction principle that is intrinsic to biologically secreted materials. This process emerged early on in the geological record, with the onset of biological mineralization. The phylum Brachiopoda is a marine animal group that has an excellent and continuous fossil record from the early Cambrian to the Recent. Throughout this time interval, the Brachiopoda secreted phosphate and carbonate shells and populated many and highly diverse marine habitats. This required great flexibility in the adaptation of soft and hard tissues to the different marine environments and living conditions. This review presents, juxtaposes and discusses the main modes of mineral and biopolymer organization in Recent, carbonate shell-producing, brachiopods. We describe shell tissue characteristics for taxa of the orders Rhynchonellida, Terebratulida, Thecideida and Craniida. We highlight modes of calcite and organic matrix assembly at the macro-, micro-, and nano-scales based on results obtained by Electron Backscatter Diffraction, Atomic Force Microscopy, Field Emission Scanning Electron Microscopy and Scanning Transmission Electron Microscopy. We show variation in composite hard tissue organization for taxa with different lifestyles, visualize nanometer-scale calcite assemblies for rhynchonellide and terebratulide fibers, highlight thecideide shell microstructure, texture and chemistry characteristics, and discuss the feasibility to use thecideide shells as archives of proxies for paleoenvironment and paleoclimate reconstructions.

Microstructure and Crystallographic Characteristics of Stenolaemate Bryozoans (Phylum Bryozoa and Class Stenolaemata)

“…In this study, we also adopt the term “tabular calcite” instead of semi-nacre also in bryozoans because, in addition, the units display a tabular habit without any consistent spiral or “screw dislocation-like” growth. The tabular calcite of bryozoans differs in its crystallographic arrangement from that of craniid brachiopods, where the c -axis is at a low angle to the tablet surface. , Another microstructure formerly described for the external surface of Hornera was “pseudofoliated calcite” . According to our observations, this is merely a variety of tabular calcite composed of imbricated calcite tablets (Figure S6).…”

“…14 It was later extended to bryozoans 12 and, subsequently, to the polygonal tablets of H. robusta. 17 Simonet Roda et al 15 proposed to replace the term semi-nacre by tabular calcite based on the lack of any relation with molluscan nacre. In this study, we also adopt the term "tabular calcite" instead of semi-nacre also in bryozoans because, in addition, the units display a tabular habit without any consistent spiral or "screw dislocation-like" growth.…”

“…The tabular calcite of bryozoans differs in its crystallographic arrangement from that of craniid brachiopods, where the c-axis is at a low angle to the tablet surface. 15,28 Another microstructure formerly described for the external surface of Hornera was "pseudofoliated calcite". 17 According to our observations, this is merely a variety of tabular calcite composed of imbricated calcite tablets (Figure S6).…”

“…robusta with electron backscatter diffraction (EBSD) , concluded (in line with Taylor and Weedon) that the c -axes were oriented perpendicular to the skeletal walls, whereas the a -axes were randomly oriented “laying predominantly in the plane of the wall”. Contrary to other groups of biomineralizers such as corals, mollusks, and brachiopods, where numerous and complete crystallographic studies of their microstructures have been carried out, ,− there is still much to learn about in bryozoans. Accordingly, we decided to conduct a thorough study of the distribution and crystallography of the microstructures of the two main groups of bryozoans, cheilostomes and cyclostomes.…”

Multi-proxy assessment of brachiopod shell calcite as a potential archive of seawater temperature and oxygen isotope composition

“…The umbo, edges and the muscle scar area were avoided because they record major kinetic or metabolic effects (Carpenter and Lohmann, 1995;Auclair et al, 2003;Parkinson et al, 2005;Yamamoto et al, 2010b;Ullmann et al, 2017;Romanin et al, 2018), and sampling was focused on the middle part of the shell. Considering the complex structure of brachiopod shells (Simonet Roda et al, 2022), the unambiguous distinctions between the different shell layers could not be performed during sampling. In this study, we differentiate the outer layers, i.e.…”