Nymphon gracile has a smooth body up to 1 cm long. Its body segments are longer than they are wide and the proboscis is at least twice as long as it is wide. The eight legs are long and slender and roughly 3 to 4 times the length of the body. Chelifores of Nymphon gracile have well developed chela and the palps consist of 5 segments, the ultimate and penultimate segments being equal in length. Although the body is translucent, there is a visible, pink alimentary canal. Ovigerous legs occur in both sexes and have prominent toothed spines which are used to clean the surface of the body. Nymphon gracile commonly migrate into the sublittoral to breed during winter months. Males then carry the eggs back to the intertidal zone sometime in March or April. Nymphon gracile generally reach maturity within 5 months and average life expectancy is about a year.