On the organization of the lophophore in phoronids (Lophophorata: Phoronida)

The organization of the lophophore is the main feature used for the identification of phoronid species. The structure of the lophophore and tentacles in seven phoronid species (Phoronis ovalis, P. ijimai, P. hippocrepia, P. svetlanae, P. australis, Phoronopsis harmeri, and Ph. malakhovi) collected in different areas of the World Ocean was studied. Two new patterns of the phoronid lophophore structure were found: transition to horseshoe-shaped (as in P. ovalis from Aniva Bay and in P. ijimai from the coast of Iturup Island, Sea of Okhotsk) and transition to spiral (in burrowing specimens P. hippocrepia from Aniva Bay, P. svetlanae and Ph. harmeri from Vostok Bay, Sea of Japan). For the first time it was shown that phoronid species with different types of the lophophore structure possess different kinds of tentacles. Thus, five types of phoronid tentacles were identified that vary in the shape of their cross section: rounded, oval, ellipsoid, rectangular, and skittle-shaped. A correlation was found between lophophore organization and the type of tentacles in phoronids. A table of the correlation between body size, lophophore organization, tentacle structure, and mode of life in different phoronid species is proposed.