When feeding, the large, translucent proboscis is everted like a sock turned inside out by muscles increasing the hydrostatic pressure of the haemolymph within it. The proboscis is rarely seen as it is usually inverted into the body of T. arctica when not in use. This image, of a conveniently transparent species, shows that unitary ascidians are eaten.
1: partially retracted mantle of T. arctica.
2: transparent test of unitary ascidian, Corella parallelogramma.
3: everted feeding proboscis of T. arctica inserted deep into ascidian.
4: faint, dull orange oesophagus within translucent proboscis.
5: translucent orange tip of proboscis with internal, opaque, orange, bullet shaped buccal mass.
6: inhalent respiratory siphon of T. arctica. Many on-line images of gastropods mistake the frequently extended respiratory siphon for the more rarely seen proboscis.
Årsundøya, Norway. April 2018. © N. Aukun.