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An ultrastructural study of settlement and metamorphosis in sponge larvae
Bergquist, P.R.; Green, C.R. (1977). An ultrastructural study of settlement and metamorphosis in sponge larvae. Cah. Biol. Mar. 18(3): 289-302 (6plates)
In: Cahiers de Biologie Marine. Station Biologique de Roscoff: Paris. ISSN 0007-9723, more
Peer reviewed article  

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Keyword
    Marine

Authors  Top 
  • Bergquist, P.R.
  • Green, C.R.

Abstract
    Major events during the settlement and metamorphosis of the larvae of three species of Demospongiae are described, following study using a method whereby larvae are fixed in situ after settlement and then sectioned for light and electron microscopy. Scanning micrographs of sponge larvae reveal the existence of metachronal ciliary patterns. Particular attention was paid to the structure of the larval ciliated layer in thin section and freeze fracture electron microscopy. No characteristic junctional structures were observed, although some organization of membrane particles, and some peculiar aggregations of volcano-like membrane structures, were seen. During attachment to the substrate, the basal lamina undergoes chemical elaboration in similar fashion to exudate from fibroblasts in culture. In the course of metamorphosis, choanocytes appear to originate from archaeocytes. There is no evidence to suggest that they arise from cells of the larval ciliated layer which later migrate into the sponge mesobyl. The first evidence of canal formation is the secretion of a fine collagen guide fibril by archaeocytes, which align around the fibril, and differentiate into the endopinacocytes, was observed.

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