Observations on the ciliary feeding mechanism of the brachiopod Crania anomala



In young Crania anomala with a trocholophe or an early schizolophe one inhalant current enters the anterior gape, filters past the single bell-shaped cirrous basket and spills out diffusely as exhalant current both anteriorly and laterally. Late schizolophe or early spirolophe forms two separate cirrous baskets which produce two separate inhalant currents: the exhalant current still diffuses out anteriorly and laterally. In later stages either one single exhalant current comes out at the anteromedial region, or three exhalant currents, including an additional one at each posterolateral region.

The roof of the visceral cavity is attached in five places to the dorsal valve of Crania to form a mantle recess, an anterior passage and two lateral passages. A hole bored through the dorsal valve into the mantle recess or the anterior passage lets out exhalant current. The palaeobiological significance of this lies in the possible use of the hole in the perforate shell valve of the siphonotretid fossil inarticulate Schizambon australis as an exhalant opening. In this species the hole leads into the mantle recess, which also communicates via a lateral passage with each posterolateral part of the mantle space.