(phylum Hemichordata, class Pterobranchia)
An order of free, unattached associations of individual zooids. The mesosoma bears several pairs of arms. The gonads are paired, with a pair of gonadial openings. There is one pair of branchial pores. The skeleton (coenoecium) is very variable and usually irregular in form. The first known occurrence of cephalodiscids is in the Early Ordovician.
Subjects: Zoology and Animal Sciences.