Microanatomy of the trophosome region of Paracatenula cf. polyhymnia Catenulida, Platyhelminthes and its intracellular symbiontsReport as inadecuate

Microanatomy of the trophosome region of Paracatenula cf. polyhymnia Catenulida, Platyhelminthes and its intracellular symbionts - Download this document for free, or read online. Document in PDF available to download.


, Volume 130, Issue 4, pp 261–271

First Online: 14 September 2011Received: 13 June 2011Revised: 11 August 2011Accepted: 13 August 2011


Marine catenulid platyhelminths of the genus Paracatenula lack mouth, pharynx and gut. They live in a symbiosis with intracellular bacteria which are restricted to the body region posterior to the brain. The symbiont-housing cells bacteriocytes collectively form the trophosome tissue, which functionally replaces the digestive tract. It constitutes the largest part of the body and is the most important synapomorphy of this group. While some other features of the Paracatenula anatomy have already been analyzed, an in-depth analysis of the trophosome region was missing. Here, we identify and characterize the composition of the trophosome and its surrounding tissue by analyzing series of ultra-thin cross-sections of the species Paracatenula cf. polyhymnia. For the first time, a protonephridium is detected in a Paracatenula species, but it is morphologically reduced and most likely not functional. Cells containing needle-like inclusions in the reference species Paracatenula polyhymnia Sterrer and Rieger, 1974 were thought to be sperm, and the inclusions interpreted as the sperm nucleus. Our analysis of similar cells and their inclusions by EDX and Raman microspectroscopy documents an inorganic spicule consisting of a unique magnesium–phosphate compound. Furthermore, we identify the neoblast stem cells located underneath the epidermis. Except for the modifications due to the symbiotic lifestyle and the enigmatic spicule cells, the organization of Paracatenula cf. polyhymnia conforms to that of the Catenulida in all studied aspects. Therefore, this species represents an excellent model system for further studies of host adaptation to an obligate symbiotic lifestyle.

KeywordsPlatyhelminthes Symbiosis Paracatenula Ultrastructure Trophosome Communicated by T. Bartolomaeus.

Electronic supplementary materialThe online version of this article doi:10.1007-s00435-011-0135-y contains supplementary material, which is available to authorized users.

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Author: Nikolaus Leisch - Ulrich Dirks - Harald R. Gruber-Vodicka - Markus Schmid - Wolfgang Sterrer - Jörg A. Ott

Source: https://link.springer.com/

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