sabella

from The Century Dictionary.

• noun The typical genus of Sabellidæ, containing large tubicolous cephalobranchiate marine annelids or sea-worms, with feathery or fan-like gills of remarkable delicacy and brilliancy, and greenish blood. See cut under cerebral.
• noun [lowercase] A worm of this genus, or any member of the Sabellidæ: as, the fan-sabella, S. penicillus.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Zoöl.) A genus of tubicolous annelids having a circle of plumose gills around the head.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A seaworm of the genus Sabella, around 25 cm long, which lives in tubes that it builds itself.