Brachiopoda

Abstract

Abstract Brachiopods are predominantly sessile, filter‐feeding marine invertebrates, with a ciliated, tentaculate feeding and respiratory organ called the lophophore. Their body is enclosed in a shell consisting of two unequal valves oriented dorsally and ventrally. Brachiopods appeared first in the Lower Cambrian and were dominant members of Palaeozoic benthic communities until the Permo–Triassic mass extinctions. Today represented by approximately 110 genera, brachiopods are considered a minor phylum; they live in all oceans, from the poles to the tropics, in a broad depth range from intertidal to abyssal. Brachiopods make up the two main clades: the articulate rhynchonelliforms with calcitic valves joined by a mineralised hinge, and the inarticulate linguliforms and craniiforms, whose valves are joined only by soft tissues. Articulated forms give the phylum its common name: ‘lamp shells’. In some recent molecular analyses, inarticulate brachiopods and phoronids form a single clade. Key Concepts: Brachiopods are sessile, filter‐feeding marine invertebrates with a bivalved shell and are quite distinct from bivalve molluscs. Brachiopods first appeared in the Lower Cambrian and were dominant members of Palaeozoic benthic communities until the Permo–Triassic mass extinctions. Brachiopods are considered to be a relict group but live in all oceans and in a broad depth range. Brachiopods are divided into two main groups according to the presence or absence of a mineralised tooth‐and‐socket hinge between the two valves. A lophophore in the form of two arms lined with ciliated tentacles serves as a feeding and respiratory organ. Based on some molecular analyses, phoronids may belong within Brachiopoda, forming a single clade with inarticulate brachiopods.