For extended examination, or photography, the turning of a supine snail needs to be prolonged. This can be sometimes done by holding the spire with forceps, but success varies between species and individuals. For example, Peringia ulvae may extend quickly, Littorina littorea is often slow to emerge and retreats at the slightest movement of the forceps, and Nucella lapillus may stay withdrawn for days if it has fed recently.
Other methods of restraint are needed for reluctant extenders. Small species, like P. ulvae, can be held for longer by pushing the spire into a prepared hole in the edge of a small piece of plasticine about 5mm thick. This leaves both hands free for operation of equipment, and allows one to do something else while waiting for the animal to extend. The effort exerted by the animal against the restraint produces an exposure of much more of the body than during a normal turn. Many can shift a piece of plasticine many times their own size, so weigh it down with a piece of lead. Often, after a few minutes, the snail manages to pull itself free, so check frequently for movement. For photography, avoid brightly coloured plasticine as it may reflect unwanted colour onto the specimen.
Full article of Anatomy of marine gastropods without dissection. below image 2 2 Gastropod anatomy. Transparent sole of Janolus hyalinus on undersurface of water.