NIELSEN, C.: The phylogenetic position of Entoprocta, Ectoprocta, Phoronida and Brachiopoda

Ectoprocts, phoronids and brachiopods are often dealt with under the heading Tentaculata or Lophophorata, sometimes with entoprocts as a more or less closely related group. The Lophophorata is purported to be held together by the presence of a “lophophore”, a mesosomal tentacle crown with an upstream-collecting ciliary band on monociliate cells. However, the tentacle crown of pterobranchs is an identical structure, although its ontogeny is not well documented. On the contrary, the ectoproct tentacle crown carries a ciliary sieving system with multiciliate cells and the body does not show archimery, neither during ontogeny nor during budding, so the tentacles cannot be characterized as mesosomal. The entoprocts have tentacles without coelomic canals and with a downstream-collecting ciliary system like that of trochophore larvae and adult rotifers and serpulid and sabellid annelids. Planktotrophic phoronid and brachiopod larvae develop tentacles at an early stage, but their ciliary system resembles that of echinoderm and enteropneust larvae. Ectoproct larvae are generally non-feeding, but the planktotrophic cyphonautes larvae of certain gymnolaemates have a ciliary band resembling that if the adults. The entoprocts have typical trochophore larvae and many are feeding with the downstream-collecting ciliary bands. Phoronids and brachiopods are thus morphologically on the deuterostome line, probably as the sister group of the “Neorenalia” or Deuterostomia s.str. The entoprocts are clearly spiralians, although their more precise position has not been determined. The position of the ectoprocts is uncertain, but nothing in their morphology indicate deuterostome affinities; certain details in their metamorphosis may point to a relationship with the entoprocts.