Sipunculus (Sipunculus) lomonossovi Murina, 1968  

Sipunculus lomonossovi has a transparent body wall and lives in deep cold waters. This species was described based on one specimen and has a questionable status according Cutler and Cutler (1985). It is similar to two other congeneric species S. nudus and S. novergicus but they are separated by differences in internal characteristics such as brain shape and numbers of LMBs and in their differing habitats.