Tentacular apparatus ultrastructure in the larva of Bolinopsis infundibulum (Lobata: Ctenophora)
Résumé
Most ctenophores have a tentacular apparatus, which plays some role in their feeding. Tentacle structure has been described in adults of only three ctenophore species, but the larval tentacles have remained completely unstudied. We made a light and electron microscopic study of the tentacular apparatus in the larvae of Bolinopsis infundibulum from the White Sea. The tentacular apparatus of B. infundibulum larvae consists of the tentacle proper and the tentacle root. The former contains terminally differentiated cells, while the latter contains stem cells and cells undergoing differentiation. The core of the tentacle is formed by myo-cytes, and its epidermis contains colloblasts (hunting cells), wall cells, degenerating cask cells, refractive vesicles, and ciliated sensory cells. Stem cells, colloblasts, and cask cells at various stages of differentiation and putative myo-cytes progenitors were revealed in the tentacle root. Two different populations of the stem cells in the tentacle root give rise to epidermal (colloblasts and cask cells) and mesogleal (myocytes) cell lines. Nervous elements, glandular cells, and basal lamina were not found. Step-by-step differentiation of colloblasts and cask cells is described.