Morphogenesis of tunic spines in the sea peach Halocynthia papillosa: ultrastructural and cytochemical aspects
Lübbering, B.; Goffinet, G. (1993). Morphogenesis of tunic spines in the sea peach Halocynthia papillosa: ultrastructural and cytochemical aspects. Belg. J. Zool. 123(Suppl. 1): 47
In: Belgian Journal of Zoology. Koninklijke Belgische Vereniging voor Dierkunde = Société royale zoologique de Belgique: Gent. ISSN 0777-6276; e-ISSN 2295-0451, more
Multipointed protrusions, the tunic spines, characterise the adult tunic of Halocynthia papillosa. Ultrastructural and cytochemical methods were employed to survey tunic morphogenesis during early developmental stages of Halocynthia papillosa. The first tunic elements are secreted at the initial tail bud stage. Already at stage M 2d (2 days after the onset of metamorphosis), the first spines are formed, but spine morphogenesis at this stage is quite different from spine morphogenesis at later stages. At early stages, claw-like protrusions bud from swellings of the tunic. When new spines are formed at later stages, first a small multipointed spine appears. Subsequently a cuticular plate develops, carrying the spine which eventually elongates and thickens. By then, the fully developed spine resembles the spines that cover the surface of the adult tunic. From stage M 2d onwards fibro-granular material is found in the fundamentallayer of the juvenile tunic. First, this material is found only in close proximity to developing spines. Later on, it is distributed throughout the whole fundamentallayer, but it is concentrated near the tips of the spines where it joins the cuticle. The cytochemical test for thiol groups (silver methenamine) demonstrates that the fibro-granular material consists of sulphur rich proteins. It is synthesised in epidermal granules and discharged into the tunic. Although the mode of displacement is not understood, this material obviously crosses the fundamentallayer of the tunic and joins the cuticle in regions of spine morphogenesis. X-ray microanalysis on the adult tunic confirms that the cuticle of spines contains sulphur.
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