Misshapen spines in sea-urchins of the family Echinothuridae were observed several times by the famous Danish echinoderm specialist, the late Dr. Th. Mortensen. The swellings were caused, he discovered, by a small crustacean inhabiting a cavity in the swelling. He entrusted his material to H. J. HANSEN, who published a detailed study on the phenomenon in 1902, whereas new samples discovered later on were studied by K. STEPHENSEN (1935). Apart from these two publications, no new observations concerning these galls in sea-urchin spines have been published. HANSEN gives an illustration of the transformed spine (1902, pl. XV fig. 1); this illustration, copied in the present paper (fig. 1a) gives the impression that the parasite inhabits a thickened part at the top of the host’s spines. Hansen must have dealt with a spine whose distal part was broken off or he figured one of the club-shaped spines that normally, thus without interference of a parasite, occur in Echinothuridae. The galls caused by copepods occur always halfway the spine (our figures 1 b-d); they are not unlike birdnests glued against a stem. The swelling illustrated by Hansen is a symmetrical one, the galls actually found are asymmetrical.