Most observers consider that Actinotrocha is a highly modified Trochosphere, and this would give it some claim to be regarded as distantly related to the Entoproct Polyzoa and to other groups which have a Trochosphere larva.
From the trochosphere stage the free larvae pass into that of "veligers."
This little creature, which has many of the features of a Trochosphere larva, swims about at the surface of the sea for about a month and grows rapidly.
The external surface of the trochosphere is formed of a number of ciliated test-cells.
- Free-swimming Larva (Mailer's Larva) of a Polyclad Planarian to illustrate the trochosphere-hypothesis of the origin of Platyelmia.