Turquoise arrows:
Cilia on pallial gills (1) create gentle, local, inhalent, respiratory water currents from adjacent shell-rim onto gills, and exhalent current below gills back to shell-rim (Yonge & Thompson, 1976).

Thin blue arrows:
Route of cilia-transport of faecal matter from the anus and excreta and ova/sperm from the urogenital openings in nuchal cavity(2) to accumulate at middle of right side (dotted arrows = route concealed by foot). The accumulations are expelled by periodic sharp contraction of pedal-retractor muscle clamping shell down and forcefully flushing them out with water. (Fretter & Graham, 1994).

Thick blue arrows
Water current on specimens less than 10 mm long from exterior into nuchal cavity (2) and thence assisting ciliary action to carry faeces, excreta and sperm/ova to the exit point on the right side.

Length 30 mm. Lleyn, Wales. September 2015.