Alitta virens is an annelid worm

Annelid

The annelids , formally called Annelida , are a large phylum of segmented worms, with over 17,000 modern species including ragworms, earthworms and leeches...

 that burrow

Burrow

A burrow is a hole or tunnel dug into the ground by an animal to create a space suitable for habitation, temporary refuge, or as a byproduct of locomotion. Burrows provide a form of shelter against predation and exposure to the elements, so the burrowing way of life is quite popular among the...

s in wet sand and mud. It is classified as a polychaete

Polychaete

The Polychaeta or polychaetes are a class of annelid worms, generally marine. Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are made of chitin. Indeed, polychaetes are sometimes referred to as bristle worms. More than 10,000...

 in the family Nereididae

Nereididae

Nereididae are a family of polychaete worms. It contains about 500 – mostly marine – species grouped into 42 genera. They may be commonly called ragworms or clam worms.-Characteristics:...

 .

Sandworms make up a large part of the live sea-bait

Fishing bait

Fishing bait is any substance used to attract and catch fish, e.g. on the end of a fishing hook, or inside a fish trap. Traditionally, nightcrawlers, insects, and smaller bait fish have been used for this purpose...

 industry. "Sandworming", or the harvesting of sandworms from mudflats, employs over 1,000 people in Maine

Maine

Maine is a state in the New England region of the northeastern United States, bordered by the Atlantic Ocean to the east and south, New Hampshire to the west, and the Canadian provinces of Quebec to the northwest and New Brunswick to the northeast. Maine is both the northernmost and easternmost...

. , the population of sandworms had diminished greatly over the preceding few years due in large part to overharvesting before the worms are able to reproduce by spawning

Spawn (biology)

Spawn refers to the eggs and sperm released or deposited, usually into water, by aquatic animals. As a verb, spawn refers to the process of releasing the eggs and sperm, also called spawning...

.

Sandworms eat seaweed

Seaweed

Seaweed is a loose, colloquial term encompassing macroscopic, multicellular, benthic marine algae. The term includes some members of the red, brown and green algae...

 and microorganisms. They have many distinctive traits, including

• often reaching great length, sometimes exceeding four feet
• numerous, highly vascularized
  Vascularity
  Vascularity, in bodybuilding, is the condition of having prominent, visible veins.Vascularity is enhanced by extremely low body fat , low retained water, high blood pressure and muscle engorgement. Genetics will affect vascularity as well as ambient temperature. Some bodybuilders use topical...
  
   parapodia along both sides of their bodies
• blue heads with two large pincer teeth, said to occasionally bite humans

The parapodia function both as external gill

Gill

A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...

s (the animal's primary respiratory surfaces), and as means of locomotion (appearing much like short legs).