Asexual reproduction in homoscleromorph sponges (Porifera; Homoscleromorpha) |
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Authors: | Alexander V Ereskovsky Daria B Tokina |
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Institution: | (1) Department of Embryology, Faculty of Biology and Soils, Saint-Petersburg State University, Universitetskaja nab. 7/9, 199034 St. Petersburg, Russia;(2) Zoological Institute, Russian Academy of Sciences, Universitetskaja nab. 1, 199034 St. Petersburg, Russia;(3) Centre d’Océanologie de Marseille, Station marine d’Endoume, Université de la Méditerranée, UMR-CNRS 6540, rue de la Batterie des Lions, 13007 Marseille, France |
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Abstract: | Asexual reproduction by external budding in Homoscleromorpha is reported for the first time. Two Mediterranean sponge species
were studied, Oscarella lobularis and O. tuberculata. Buds are formed in the marginal basal part of sponge. Budding takes from 1 to 4 days and is defined in three budding stages.
First, small irregular protuberances, consisting of external parental tissue, are formed. Second, they elongate and acquire
more regular, nipple-like shape. These protuberances are tube like, their internal cavity derived from parental exhalant canal.
The wall consists of three layers: (a) external layer is flagellated exopinacoderm, (b) internal one is flagellated endopinacoderm
and (c) intermediate one is a thin layer of mesohyl. Third, a spherical bud with a large central cavity is formed. During
budding, we did not observe cell proliferation or transdifferentiation either in budding zone or in any special mitotically
active region. The bud attached to the substrate is similar to the rhagon developing after larva metamorphosis, it has a syconoid
organization. Morphogenetically, budding in Oscarella differes from that in other sponges. Occurring by epithelial morphogenesis, it is similar to morphallaxis during regeneration.
The presence in Homoscleromorpha of an epithelial morphogenesis is unique among sponges. This feature is shared by Homoscleromorpha
and Eumetazoa. |
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