'Sea mouse' definitions:

Definition of 'sea mouse'

(from WordNet)
noun
Any of several large worms having a broad flattened body with a mat of coarse hairs covering the back

Definition of 'Sea mouse'

From: GCIDE
  • Sea mouse \Sea" mouse`\ (Zool.) (a) A dorsibranchiate annelid, belonging to Aphrodite and allied genera, having long, slender, hairlike setae on the sides. (b) The dunlin. [1913 Webster]