If you are in a poorly known part of the world aim to preserve six specimens of each species. Collecting nudibranchs Bringing up your finds. The easiest container to use whilst diving is a strong plastic bag.
Some people prefer smaller bags or plastic tubes.
If you use tubes, fill them with seawater so that you will be able to open them when they are under pressure. Underwater photographs of the animals in position on the rocks or food are very useful as they may give clues as to what the species was eating. Use a macro lens or extension tubes and a flashgun. Remember that a white animal will tend to over-expose so stop down if necessary. Photograph spawn coils as they may belong to the animals.