During our studies of the reproductive cycles in limpets (family Acmaeidae) we have been confronted by the lack of a method to determine sex without killing the animals. Previous studies have relied upon dissection or histological sectioning to determine sex. This note describes a technique which allows the determination of sex in patellacean limpets without killing the animal.

The tools needed are a syringe (1 cc) with a hypodermic needle (we have found that a 26 gauge, 16 mm needle works well with specimens larger than 10 mm in length), and a glass microscope slide. After removing the limpet from the substratum the shell is held with the aperture down. As the animal extends its foot downward it exposes and stretches the sides of the body wall. When the posterior portion of the body wall is fully exposed the needle is inserted approximately one third of the way up the body wall towards the shell attachment muscle. The orientation of the needle should be in line with the plane of the aperture. Penetration of the gonad can be felt by a ‘breaking through’ or sudden decrease in resistance to the progress of the needle. Care should be taken to avoid penetrating further than necessary because other organs can be easily damaged. Drawing the sample requires more force and time (approximately 10 s) than one would expect. When withdrawing the needle constant tension on the syringe plunger is necessary to keep the sample in the needle. The contents of the needle are then emptied on to the glass slide.