Differentiation and Growth of the Brachiopod Mantle

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Abstract
Cell differentiation in the mantle edge of Notosaria, Thecidelhna and Glottidia, representing respectively, the impunctate and punctate calcareous articulate and chitinophosphatic inarticulate brachiopods, is described. Comparison of electron micrographs suggests that outer epithelium which secretes periostracum and mineral shell, is separated from inner epithelium by a band of “lobate” cells, of variable width, exuding an impersistent mucopolysaccharide film or pellicle. The lobate cells always occupy the same relative position on the inner surface of the outer mantle lobe; but the outer epithelium is commonly connected with the inner surface of the periostracum by papillae and protoplasmic strands which persist during mineral deposition and ensure that both shell and attached mantle remain in situ relative to the outwardly expanding inner surface of the outer mantle lobe. In the prototypic brachiopod, the lobate cells are likely at first to have occupied the hinge of the mantel fold but later to have been displaced into their present position by the rigid outward growing edge of the mineral shell.

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