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Ultrastructure of the penicillate podia of the spatangoid echinoid Echinocardium cordatum (Echinodermata) with special emphasis on the epidermal sensory-secretory complexes
Flammang, P.; de Ridder, C.; Jangoux, M. (1991). Ultrastructure of the penicillate podia of the spatangoid echinoid Echinocardium cordatum (Echinodermata) with special emphasis on the epidermal sensory-secretory complexes. Acta Zool. (Stockh.) 72(3): 151-158. hdl.handle.net/10.1111/j.1463-6395.1991.tb00942.x
In: Acta Zoologica (Stockholm). Svenska Bokfoerlaget: Stockholm. ISSN 0001-7272, more
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Keyword
    Marine

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Abstract
    The spatangoid echinoid Echinocardium cordatum possesses specialized penicillate podia that handle sediment particles during burrowing and feeding. Epidermal complexes, which occur on podial surfaces directly contacting the sediment, each comprise four cells: a non-ciliated secretory cell containing granules rich in mucopolysaccharides (NCS cell), a ciliated secretory cell containing granules of unknown composition (CS cell), and two ciliated non-secretory cells (CNS cells). The cilium of the CS cell is subcuticular whereas that of each CNS cell traverses the cuticle. We propose that these four cells constitute a sensory-secretory complex wherein the ciliated cells are sensory cells and the secretory cells function for adhesion and de-adhesion. More exactly, an NCS cell adhesive and a CS cell de-adhesive would be sequential and would be initiated by two successive stimulations transduced by cilia when the podium touches the sediment. Cilia that first contact the sediment are those protruding through the cuticle from the CNS cells. Their stimulation would result in the secretion of an adhesive material by the NCS cells. Subsequently, the subcuticular cilia of CS cells would be stimulated when the podial digitations closely squeeze the substrate, and this would induce the secretion of a de-adhesive. These two antagonistic secretions would allow the podium to pick up and discharge sediment repetitively during burrowing and feeding.

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