Phascolion  

(From Cutler, 1994)

Small to medium size worms (less than 50 mm in length).

Common inhabitants of empty gastropod shells.

Introvert one-half to four times the trunk length.

Hooks present or absent.

Muscle layer continuous.

Tentacular crown around the mouth.

Retractor muscles modified, fusion of the dorsal and ventral pair, giving the appearance of only one or two muscles. Degree of fusion and relative size define the subgenera.

Intestine coiling loose and without axial spindle muscle.

One nephridium (generally the right one).