Montserrat Poquet

Sublethal effects of experimental exposure to mercury in European flat oyster Ostrea edulis: cell alterations and quantitative analysis of metal.

Oysters display a diversity of uptake mechanisms for metallic elements and distribution in the target organs, namely gills and the digestive gland. Various tissues of the flat oyster, Ostrea edulis, were studied following experimental exposure to 0.025 μm (5 μg l) of mercury, for up to 34 days. All animals survived the treatment. Data indicate Hg accumulation in gill tissue with a maximum concentration of 38.76 μg g dry weight after 25 days of exposure. Hg levels were lower in remaining tissues, in which the maximum concentration (18.47 mg g-1 dry weight) was reached after 18 days of exposure. After these times, concentration in both tissues decreased. Results show that oysters can accumulate Hg from the environment, without their survival being affected during the experimental period. Structural alteration of epithelial tissues of gill and digestive gland of flat oyster was comparable with effects described for other metallic elements in bivalve molluscs. Interstitial tissue was disorganized in the digestive gland, and ultrastructural changes in intracellular endomembranes were detected in epithelial cells of the digestive gland after 18 days of treatment. After 25 days, absorptive epithelial cells of gills showed highly dilated, swollen microvilli. These intracellular alterations are parameters of the incipient response to the accumulation of mercury.

Ultrastructure and cytochemistry of the integument of Modiolicola gracilis, parasitic copepod in mussel gills (Mytilus galloprovincialis and Mytilus edulis)

Of mussels taken from the Ebro Delta River (E. Spain), 3% have a nonmodified copepod, Modiolicola gracilis, in the gill tissues. The cuticle of different segments of the body has an epicuticle with two layers, which show external microvilli‐like projections. Weakly positive reactivity to the PTA technique has been detected in the external region. The procuticle has the helicoidal architecture of the chitinous tegument in arthropods, whereas the cuticle shows discontinuities in the regions of ducts in tegumental glands.

Peculiar features of the sperm of a calanoid copepod Arctodiaptomus salinus

Abstract The spermatophore and spermatozoon of the calanoid copepod A. salinus , were investigated by light and electron microscopies . Mature spermatozoa were found within the spermatophore in the seminal vesicle at the end of the deferent duct. The cells measured 2–3 μm in diameter and were almost spherical; the nucleus was mixed with the cytoplasm as no envelope was present to separate them. They lack flagellum and any acrosome-like structure. The dispersed chromatin forms small granules surrounding the mitochondria, characterised by a small number of highly modified cristae. Under the plasmatic membrane, a group of electron-dense lamina enclose the whole cytoplasm. In the final phase of spermiogenesis, the dismantling of the nuclear envelope, the formation of chromatin granules and the modification of mitochondria occur. This process takes place simultaneously with the synthesis of the components of the spermatophore by the epithelial cells of the deferent duct. All these characteristics of the sperm of A. salinus identify it as being a peculiar case among copepoda.