Haminoea navicula was abundant on the muddy river bed. Hundreds were in single file processions. By touch and/or chemoreception, each individual followed the mucus trail, visible when it crossed green alga (2), left by the preceding individual.
Parapodial lobes hide much of the shell; their edges often do not meet (1); they may meet for a short distance on the dorsum medially but with no, or insignificant, overlap.
3: shell. 4: posterior pallial lobe. 5: head. 6: dark patch between eyes. 7: medial white line behind dark patch. River Deben, Suffolk, England. August 2020. © A. Price.