1: penis. 2: siphon. 3: eye (seen through translucent tentacle). 4: proboscis pouch. 5: opercular disc. 6: mantle.
Live examination cannot replace skilled detailed dissection of internal anatomy, but for those who lack the skill, equipment or inclination to dissect, it can provide much interest and information. For studying external anatomy, live examination often has the advantage as the positions of organs on a dissected animal depend on the way the mantle cavity is opened, and they may be collapsed or contracted even when the animal was narcotised and relaxed before killing. On live animals the organs are in more predictable positions and more likely to be expanded . Graham, (1988), writing of Nucella lapillus, states, “The head is a flat transverse ridge…Each tentacle has an eye about one third of its length up from the base”. This description may be based on collapsed dead material as all live specimens that I have examined had the eye about two thirds of the way up the fully expanded tentacle, and the head was not flat.
Full article of Anatomy of marine gastropods without dissection. below image 2 2 Gastropod anatomy. Transparent sole of Janolus hyalinus on undersurface of water.