Ecdysozoa Phylogenetic tree (7)

Description:

• Protostome (4)
• Free-living benthic marine worms with an eversible proboscis (3)
• Range in size from 1 mm (early instars may be as small as 50 µm) to more than 40 cm in length (3)
  
• The body is cylindrical and includes an introvert that includes spines (retractable and invertible proboscis), a neck-like collar, a trunk, and sometimes a "tail" (3)
  

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Body Structure (5)

Nutrition(3):

• Feed on soft-bodied invertebrates such as polychaete worms and other priapulans
• While feeding, a portion of the toothed pharynx is ejected through the mouth at the end of the extended introvert, then retracted together with the prey item
  

Habitat(3):

• Found from polar seas to the tropics and from ocean trenches to the intertidal zone 
  
• Burrow actively in relatively fine marine sediments, primarily in boreal and cold temperate seas, burrow or live interstitially among sediment particles 
  

Reproduction(3):

• Separate sexes
• Males spawn first, then females; fertilization is external
• Nearly all species have a non-swimming benthic larval stage, which may last as long as one to two years
• Larvae live in mud and are probably detritivores
  

Conservation Status(6):

• Not considered threatened or endangered

Interesting facts:

• Commonly known as the penis worm (3)
• Has helped researchers to further study the evolution of digestion since they are categorized as protostomes but develops like a deuterostome (4)