magelonidæ

from The Century Dictionary.

• A family of marine, sand-inhabiting polychætous worms, having the body divisible into two regions by differences in the setæ, the prostomium large and flat, two long peristomial cirri, and a large eversible buccal region. The blood is madder-pink when oxygenated, but colorless when deoxidized. It contains the single genus Magelona.