Classification and Phylogenetic Significance of Molluscan Shell Microstructure

Abstract

Like most classifications of molluscan shell microstructure published during the past 25 years (e.g., MacClintock, 1967; Kobayashi, 1964, 1971; Taylor, Kennedy and Hall, 1969, 1973; Grégoire, 1972a), the present one is based largely on Bøggild's (1930) monographic work, redefined from a modern perspective of combined light and scanning electron microscopy. However, this is the first attempt to integrate shell microstructure terminology for mollusks with that employed by students of bryozoan and brachiopod shell microstructure (e.g., Williams, 1968a,b, 1970, 1973; Williams and Wright, 1970; Armstrong 1968, 1969; Sandberg, 1971, 1977; Brunton, 1972; MacKinnon, 1974, 1977; MacKinnon and Williams, 1974; Iwata, 1981, 1982). An integration of nomenclatorial schemes is desirable for purposes of interphylum comparison, and is presently needed because there is considerable overlap and inconsistency in the application of microstructural terminology even within single molluscan classes. The present synthesis of shell microstructure nomenclature is possible primarily because of the extensive data base of invertebrate shell mineralogy, microstructure and especially ultrastructure published in more than 300 references in the past 15 years. To these data, the authors have contributed original information of shell mineralogy and microstructure for scores of Recent and fossil mollusks, brachiopods and bryozoans, with a clear emphasis on bivalved mollusks. Many inadequately described microstructure terms have been reanalyzed during the course of this study, either by examining species cited in the literature, or by using closely related species. Perhaps because they are better studied, but probably for other reasons as well, the diversity of molluscan shell microstructures is considerably greater than that of brachiopods and bryozoans combined (Carter, 1979). Consequently, most of the present nomenclature is based on mollusks, and only three of the major microstructural arrangements described in this guide (crossed bladed, semi-nacreous and semi-foliated) were known first in brachiopods or bryozoans and later recognized in molluscs.

Three-dimensional structure of the shell plate assembly of the chiton Tonicella marmorea and its biomechanical consequences

“…Macroscopic morphological chiton terminology used was defined and/or standardized by Schwabe (2010) while chiton shell plate layer nomenclature used was derived from Bergenhayn (1930) and Russo (1978, 1980). Molluscan microstructure terminology used was defined by Taylor and Layman (1972) and Carter and Clark (1985).…”

“…Similar orientation, thickness, and branching irregularities of the first order lamellae of the crossed-lamellar layers of the shell plates of T. marmorea have also been reported in the shells of other mollusks (Currey and Kohn, 1976;Taylor and Reid, 1990;Wilmot et al, 1992). The width of first order lamellae in the crossed-lamellar layers of the shell plates of T. marmorea (1-2 lm), Acanthopleura brevispinosa (1.7-5 lm) (Wilmot et al, 1992), Chiton olivaceus (2-3 lm) (Laghi and Russo, 1978), Lepidopleurus cajetanus ($3 lm) (Laghi and Russo, 1980), Liolophura japonica ($3 lm) (Chen, 2010), as well as the range found in 36 chiton species representing 19 genera (3-5 lm) (Haas, 1972) lies in the extreme lower end of the range (1-40 lm) found in crossed-lamellar microstructures across Mollusca (Carter and Clark, 1985;Wilmot et al, 1992). As previously observed by Haas (1976Haas ( , 1981, Poulicek and Kreusch (1983), and Carter and Hall (1990), the simple crossed-lamellar structures present in chiton shell plates are devoid of well-defined second order lamellae.…”

Microstructure and crystallographic texture of Charonia lampas lampas shell

“…We describe the layer microstructures using the terminology of Carter and Clark (1985), but we emphasise that these definitions only represent a terminology (the names are convenient brief summaries of observed morphologies), not necessarily a statement of homology (Chateigner et al, 2000). We use 'first-order' and 'second-order' lamellae to describe increasingly fine microstructural elements with morphological distinction.…”

Towards a phylogeny of gastropod molluscs: an analysis using morphological characters

“…Nacreous shell structure ('mother of pearl') is composed of polygonal, aragonitic laminar tablets arranged in broad, regularly formed, parallel sheets (Carter & Clark, 1985). Crenshaw (1 990) considered nacre the simplest molluscan shell structure, although it is energetically expensive to produce.…”