Nassarius fraterculus is a species of sea snail, a marine gastropod mollusk in the family Nassariidae, the Nassa mud snails or dog whelks.

[1] The shell grows to a length of 10 mm.

This marine species occurs off China, Korea and Japan, but has been introduced to the Pacific Northwest of North America through commercial oyster shipments.

[2] N. fraterculus inhabits intertidal regions, foraging on crushed mussels.

[3] In the Pacific Northwest, N. fraterculus has been shown to benefit from the presence of Batillaria attramentaria, another invasive species.