Abstract
We studied the embryonic development of the phoronid Phoronis ijimai Oka, 1897. The egg cleavage is radial. The fourth and fifth cleavage furrows extend along the meridian of the egg. The blastula is flattened. Gastrulation occurs by a combination of epiboly, bending, and invagination. The mesoderm originates from two sources. The anterior mesoderm arises through immigration and gives rise to the first and second coeloms. The third coelomic mesoderm originates enterocoelically from the hindgut. The newly hatched larva has preoral and postoral ciliary bands, which can be compared with the corresponding ciliary bands of dipleurula and with the prototroch and metatroch of trochophore larvae.
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