mermaid's-glove

from The Century Dictionary.

• noun A name given to the largest of British sponges, Halichondria oculata, from its tendency to branch into a form bearing a remote resemblance to a glove with extended fingers. It sometimes attains a height of 2 feet.
• noun A kind of alcyonarian polyp, Alcyonium digitatum: same as dead-men's-finagers.