The periodicity of sexual elements and soft tissue modifications during the life cycle of the hypercalcified sponge Petrobiona massiliana was investigated monthly from June 2006 to November 2007. Sexual reproduction, likely regulated by seawater temperatures, occurred during more than half of the year (from early April to late October); 70% of the samples appeared reproductively active. Specimens of P. massiliana displayed a high plasticity of tissue organization, allowing modulation and rearrangement of their aquiferous systems in response to life cycle phases and environmental changes. Permanent changes were observed in the basal region of the choanosome in non-reproductive specimens, such as disorganization/ restructuring events leading to remodeling of the aquiferous system. Periodic modifications occurring during sexual reproduction included the transformation of choanocytes from a typical form to hourglass and vespiform shapes, and more global disorganization of the basal region of the choanosome during provisioning of oocytes and embryos, followed by restructuring after release of the larvae. Finally, episodic disorganization/reorganization phenomena occurred in a few specimens after unfavorable environmental conditions (e.g., decreasing seawater temperatures). Histological and ultrastructural observations of storage cells, located in peculiar trabecular tracts, suggest a transdifferentiation capacity that allows such soft tissue dynamics.
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Seasonality estimations using incremental data usually suffer from small sample sizes and from the lack of comparison with sufficiently large modern samples. The present contribution reports on incremental studies carried out on large assemblages of plaice (Pleuronectes platessa) and haddock (Melanogrammus aeglefinus) from a late medieval fishing village (Raversijde, Belgium) on the North Sea coast. In an attempt to refine previous seasonality estimates made for this site, and to expand conclusions concerning general methodology, extensive monthly samples of modern otoliths of these species, caught within the North Sea, have also been investigated. The modern material shows that the timing of the seasonal changes in the edge type (hyaline or opaque) of the otoliths is extremely variable and that it is dependent on the fishing ground, the year considered, and the age of the fish. It also appears that the increase of the marginal increment thickness is highly variable, to such an extent that the thickness of the last increment of a single otolith is mostly useless for seasonality estimation. Where large archaeological otolith assemblages can be studied, preferably from single depositional events, seasonality determination becomes possible on the condition, however, that the archaeological assemblage corresponds to fish that were captured during their period of fast growth. The growth ring study on the otoliths from Raversijde shows that plaice fishing took place in spring and that it was preceded by a haddock fishing season, probably in late winter/early spring.
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