The extinct plumulitid machaeridians look like modern bristleworms
, whose stout walking limbs bear long bundles of bristles; however, on their backs, machaeridians carried a set of mineralized plates.
Plumulitids were annelid worms - the group including earthworms, bristleworms
and leeches, today found everywhere from the deepest sea to the soil in your yard.
Levin's group is studying bristleworms
, in particular why so many from the family Dorvilleidae inhabit these seeps (17 species so far, including 10 in one genus).