Cyphonautes

It is triangular in profile with a heavily ciliated band called the corona at the base of the triangle and a sense organ at the apex (cypho-, bent; nautes, sailor).

Muscles connected to the valves can quickly narrow the slender aperture at the base of the triangle, expelling most of the fluid volume in a sort of a sneeze that can flush undesirable material that enters the funnel.

Combined with the action of long muscle fibers connected to the apical organ and corona, the entire body can transiently collapse between the valves.

Once the cyphonautes selects a settlement site, metamorphosis begins with the rapid collapse of the triangle: the valves are pulled flat against the substrate and the internal sac spreads out beneath them.

Jägerston[3] argued that resemblances between the cyphonautes and the actinotrocha larva of a phoronid seems to show a relationship between them, sketching an outline deriving the latter from the former; Farmer,[4] however, pointed out the proposed evolutionary sequence could go either way.