The Collaborative International Dictionary
Sea thongs
Sea thongs \Sea" thongs`\ (?; 115). (Bot.) A kind of blackish seaweed ( Himanthalia lorea) found on the northern coasts of the Atlantic. It has a thonglike forking process rising from a top-shaped base.
Wiktionary
sea thongs
n. A kind of blackish seaweed (''Himanthalia elongata'') found on the northern coasts of the Atlantic, with a thong-like forking process rising from a top-shaped base.