These worms have several apparently simple features and, as their name suggests, they are often considered to be the most primitive nemerteans.

Tubulanids are commonly encountered in rocky areas of intertidal zones in the northern hemisphere.

They are often bright orange or have very distinctive banding and or stripes and can be many meters long, although only a few mm thick.

Heteronemertea is a monophyletic grouping of about 500 species, containing genera such as Lineus and Cerebratulus and including the largest and most muscular nemerteans.

A trace fossil genus called Archisymplectes from the Pennsylvanian found in central Illinois was formerly placed in this subclass, but is now considered a Palaeonemertea, if indeed it is an Anopla.