Observations on the ciliary feeding mechanism of the brachiopod Crania anomala

Abstract

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.

Earliest ontogeny of Early Palaeozoic Craniiformea: implications for brachiopod phylogeny

“…The differentiation of the lophophore and internal organs (such as a nervous system, nephridia and gonads) are still unknown for craniids, but it is clear that the lophophore is also formed after settlement (Nielsen 1991). A median tentacle is present at the growth stage with three pairs of lophophore tentacles, but it is lost before the time when the lophophore has acquired six pairs of tentacles (Rowell 1960; Chuang 1974). The presence of a median tentacle in the lophophore of juvenile Novocrania was questioned by Lüter ( in Williams et al.…”

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

“…2a). Craniid brachiopods have an anus, found at the posterior of the body ( Figure 4B, adapted from Williams et al 1997), and Chuang (1974) suggested that this current is the means of removing wastes. In adult N. anomala, at the anterior apex of the body wall, there is a distance between the body surface and the dorsal valve of 0.2 mm when the valves are closed and 0.9-1.2 mm when the valves are open (Chuang 1974).…”

“…the dorsal mantle cilia create inhalant currents from the posterior commissure that flow anteriorly through the mantle recess, and also lateromedially between the posterior and anterior adductors, that become part of the anterior median exhalant current created by the lophophore (Figure 4A, adapted from Orton 1914, fig. 2 andChuang 1974, fig. 2a).…”

“…Only the posterior and anterior adductor muscles, median unpaired muscle, oblique internal muscles, small anterior muscles and support structure attach to the dorsal valve ( Figure 1I). This creates a Rueckenhoehle (Blochmann 1892) or mantle recess (Chuang 1974) (Figure 1G and I). In lateral view the body is wedge shaped, highest anteriorly and lowest posteriorly ( Figure 1I).…”

“…In adult N. anomala, at the anterior apex of the body wall, there is a distance between the body surface and the dorsal valve of 0.2 mm when the valves are closed and 0.9-1.2 mm when the valves are open (Chuang 1974). Above the apex is a small opening between the small anterior muscles (Chuang 1974), herein termed the anterior passage ( Figures 1H, and 4A), for the posterior-anterior dorsal mantle cilia current to pass through.…”