In the family Pyuridae the larval and post-larval stages are known only in Halocynthia pyriformis (Rathke) and Boltenia echinata (L.). Berrill (1948) has pointed out that this is the least specialized family of the Pleurogona and that its larvae are therefore of particular interest.

On 1 August 1950 specimens of Pyura squamulosa (Alder), up to 36 by 30 mm., were collected from boulders at low-water level in the Sound of Kerrera, Argyll. They were taken on the following day to the Marine Station, Millport, and there kept in running sea water until 4 August, when artificial fertilizations were carried out.