Proliferating activity in a bryozoan lophophore

Area of Science:

• Marine Biology
• Invertebrate Zoology
• Cell Biology

Background:

• Bryozoans are colonial marine animals with specialized feeding structures called lophophores.
• Colony growth (astogeny) can alter water flow, necessitating changes in lophophore shape.
• Tentacle growth mechanisms in bryozoans, particularly in adult polypides, were previously undescribed.

Purpose of the Study:

• To investigate cell proliferation and tentacle growth in adult bryozoan polypides.
• To test the hypothesis of intercalary tentacle growth at the lophophore base.
• To describe the ultrastructure of the lophophore base and identify potential stem cell niches.

Main Methods:

• Comparison of S-phase and mitotic cell distribution in young and adult polypides of three Gymnolaemata species.
• Detailed ultrastructural analysis of the oral region and ciliated pits.
• Tentacle regeneration experiments in Electra pilosa.

Main Results:

• Cell proliferation, indicative of stem cells, was identified in the ciliated pits and oral region of polypides.
• These sites support intercalary tentacle growth, enabling lophophore shape alteration.
• Deuterosome-like structures were observed during kinetosome biogenesis.
• Only non-ciliated epidermal cells contribute to wound healing in tentacle regeneration.

Conclusions:

• Intercalary growth at the lophophore base allows bryozoan polypides to adapt their feeding apparatus to changing colony conditions.
• Ciliated pits and oral regions serve as stem cell niches for tentacle elongation.
• Tentacle regeneration in Electra pilosa is a slow morphallactic process involving specific cell types.