, Volume 109, Issue 2, pp 113–122 | Cite as

Ultrastructure and relationship between protonephridia and metanephridia in Phoronis muelleri (Phoronida)

  • Thomas Bartolomaeus


The actinotrocha of Phoronis muelleri has one pair of ectodermally derived, monociliated protonephridia. The duct runs mainly between the epidermis and the lining of the hyposphere coelom, pierces the septum and extends into the blastocoel. The proximal part is branched and closed up by terminal complexes consisting of two morphologically different cells which both serve filtration. During metamorphosis, the terminal complexes and the branches of the duct are cast off. The cells degenerate, pass into the remaining duct and are endocytosed by the duct cells. After metamorphosis the remaining part of the protonephridial duct is U-shaped, blindly closed and borders on the prospective lophophoral vessel. In a later stage the duct receives a ciliated funnel, which consists of monociliated epithelio-muscle cells and is a derivative of the lining of the metacoel. Thus, a part of the protonephridial duct of the larva and the whole metanephridial duct of the adult are identical. Aspects of a possible homology between phoronid nephridia and such organs in other bilaterians are discussed.


Developmental Biology Proximal Part Duct Cell Terminal Complex Protonephridial Duct 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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Copyright information

© Springer-Verlag 1989

Authors and Affiliations

  • Thomas Bartolomaeus
    • 1
  1. 1.II. Zoologisches Institut und MuseumGöttingenFederal Republic of Germany

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