Morphological and functional characterization of the ptychocyte, a stingless stinging cell

Area of Science:

• Marine Biology
• Evolutionary Biology
• Cellular Biology

Background:

• Cnidarians possess unique stinging cells (cnidocytes) that have diversified into various types.
• Nematocytes are found in all cnidarians for prey capture and defense, while ptychocytes are specific to tube anemones for tube construction.
• Understanding cnidocyte diversity offers insights into evolutionary adaptations within the phylum Cnidaria.

Purpose of the Study:

• To investigate the morphology, function, and distribution of nematocytes and ptychocytes in the tube anemone *Ceriantheopsis americana*.
• To compare the firing dynamics of cnidocytes between *C. americana* and the sea anemone *Nematostella vectensis*.
• To explore how divergent selection pressures have influenced the evolution of cnidocyte firing mechanisms.

Main Methods:

• Morphological and functional examination of nematocytes and ptychocytes in *Ceriantheopsis americana*.
• Comparative analysis of cnidocyte discharge kinematics between *C. americana* and *Nematostella vectensis*.
• Microscopic analysis to identify sensory structures and associated cell types involved in tube formation.

Main Results:

• Ptychocytes in *C. americana* possess apical sensory structures, similar to those found on nematocytes.
• A dense population of multiciliated cells in the body wall of *C. americana* appears to be involved in tube formation.
• Both nematocytes and ptychocytes from *C. americana* exhibited slower firing speeds compared to nematocytes from *N. vectensis*.

Conclusions:

• The observed differences in firing speeds suggest that rapid nematocyte discharge evolved after the divergence of sea anemones and tube anemones.
• Comparative studies of cnidocyte morphology and function are crucial for reconstructing the evolutionary pathways of cnidocyte diversity.
• The findings contribute to a deeper understanding of cellular specialization and adaptation in marine invertebrates.