Turbellarian taxonomic database

Record # 17986
Author
Title
Journal
Sopott-Ehlers B, Salvenmoser W, Reiter D, Rieger R, Ehlers U (2001)
Photoreceptors in species of the Macrostomida (Plathelminthes): Ultrastructural findings and phylogenetic implications.
Zoomorphology (Berlin) 121(1):1-12

Abstract / Notes

"The submicroscopic anatomy of intracerebral and pericerebral photoreceptors in
six species of the Macrostomida is described. Cylindromacrostomum notandum,
Paramyozonaria simplex and Macrostomum hystricinum marinum possess two
rhabdomeric intracerebral photoreceptors each consisting of two pigmented cup
cells and three (C. notandum and P. simplex) or two sensory cells (M.
hystricinum marinum). In C. notandum and P. simplex two of the sensory cells
are equal in size, while the third one is much smaller. This organisation is
hypothesised as an autapomorphy of the Dolichomacrostomidae. Photoreceptors
with two mantle cells are also known for Microstomum spiculifer. Since only one
cup cell exists in representatives of nearly all other high-ranked taxa of the
Rhabditophora, it is concluded that the characteristic "two cup cells in
rhabdomeric photoreceptors" has evolved in the stem lineage of the taxon
Macrostomida or Macrostomorpha, respectively. In Myozona purpurea and
Psammomacrostomum turbanelloides rhabdomeric intracerebral photoreceptors of a
special type were encountered. These light-sensing organs consist of numerous
cells forming an ellipsoid. The surface membranes of these cells are elongated
to form filiform extensions which are tightly intertwined with each other.
Pericerebral ciliary aggregations consisting of cells with an internal cavity
into which axonemata of modified cilia project were observed in all species
mentioned above and in Bradynectes sterreri as well. Such putative
light-perceiving organs are widespread within taxa of the Plathelminthes
Rhabditophora and have been hypothesised either as homologous characteristics
or as analogous ones. With increasing examples being described it becomes
likely that pericerebral ciliary aggregations are an apomorphic ground pattern
characteristic of the Rhabditophora."

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