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Articles
Published: 2008-07-25

Niku-nuki: a useful method for anatomical and DNA studies on shell-bearing

Mollusca Gastropoda Bivalvia Scaphopoda anatomy DNA analysis soft parts specimen preparation

Abstract

Often only one or a few individuals of rare species are collected. How do we treat them as intact voucher specimens? The shell of the whole individual in formalin or alcohol will corrode or fade. In order to dissect the soft parts, you must crack or dissolve the shell. Niku-nuki, a traditional method that has been used by Japanese malacologists overcomes this dilemma. It is also applicable to minute molluscs. The outline is: 1. Prepare boiling hot freshwater, a small beaker, forceps (with fi ne tips), a small syringe, a petri dish, and a stereomicroscope; 2. When the live animal in the beaker crawls on the bottom, pour boiling hot water over the animal, which is killed immediately. Some seconds later take the specimen out of the hot water, hold it with two fi ngers of one hand and hold the forceps with another hand; 3. Under the microscope, grab the foot with the forceps and pull carefully to just separate the columellar muscle from the shell; 4. Pull the foot again in a petri dish fi lled with cold water as under 3. With coiled gastropods, unscrew the specimen by approximately ¼ whorls. If it is diffi cult to move the soft parts, inject water into the aperture gently with the syringe. Repeat it several times, then you will get an empty shell and the complete soft parts. With this method, we can obtain intact shells and soft parts for multiple purposes such as conchological observation and gross anatomy. DNA can also be extracted from those soft parts because DNA is stable at high temperature. The boiled animal can be dehydrated in alcohol. We can prevent the negative effect of DNase (by heat) and magnesium (by washing in freshwater) on the DNA.