A sandworm

Not the one from Dune.  This is a King Ragworm (Alitta virens):

An annelid worm that burrows in wet sand and mud. It is classified as a polychaete in the family Nereididae... Sandworms eat seaweed and microorganisms. They have distinctive traits, including...

• often reaching great length, sometimes exceeding four feet
• numerous, highly vascularized parapodia [The parapodia function both as external gills (the animal’s primary respiratory surfaces), and as means of locomotion (appearing much like short legs)].

Credit Alexander Semenov, via animals, animals, animals.