The muscles, body wall and valve-opening mechanism of extant craniid (inarticulated) brachiopods

Abstract

Specimens of six species of craniid brachiopod were dissected and the musculature, body wall and mantle were examined. New names are proposed for the “brachial protractor” and “brachial retractor” muscles. The “brachial elevator” muscles are part of the anterior adductor muscles, a small bundle of translucent quick-muscle partially enclosed by a larger, curving bundle of the dark-coloured slow-muscle. A new ring muscle is described. The lophophore arms are extended and retracted by the hydrostatic skeleton and brachial muscles respectively. The valves of Novocrania are probably opened by the creation of hydrostatic pressure, within a newly described coelomic chamber, by contraction of the oblique lateral muscles. Neoancistrocrania has an extra pair of dorsal mantle canals arising at the posterior and a dorsally directed pouch in the body wall.