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The epidermis of Timerete filiera (Polychaeta, Cirratulidae): Histochemical and ultrastructural analysis of the gland cells
No full textThe aim of this study was to verify whether different living conditions of Polychaeta are correlated with morphological and functional
differences in the organization of the integument. For this purpose, we decided to study the epidermis of Timarete filigera, a non-tubicolous
polychaete.With this objective in mind, we have identified the various cellular types responsible for mucous secretion in the epidermis of this
species and defined the histochemical composition of the mucus produced by different types of gland cells.
Three types of gland cells have been identified by histochemical and ultrastructural studies in the epidermis of this polychaete. The
histochemistry was carried out using standard techniques and peroxidase-labelled lectins. In type 1 cells, the secretory granules contain
neutral glycoproteins with glucosidic residues of GalNAc, Gal 1,3 GalNAc, glucosidic and/or mannosidic residues. In type 2 cells, the
secretory granules contain acid glycoproteins mainly sulphated with glucosidic residues of GalNAc, Gal 1,3 GalNAc, glucosidic and/or
mannosidic residues, and some terminal sialic acid. In type 3 cells, the residual granules have the same chemical composition as that of granules
present in type 2 cells. The secretion of these glandular mucous cells consists of mainly sulphated acidic glycoproteins and GAG resistant to
testis jaluronidase. In these cells, the residual granules have the same chemical composition as that of their secretion. The heterogeneity of
mucus composition may be correlated with its different functions
Istochimica ed ultrastruttura dell’epidermide di Branchiomma luctuosum (Polychaeta, sabellidae)
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Il ciclo sessuale della demospongia Geodia cydonium Jameson 1811: tre anni di osservazioni mediante tecnica di marcatura individuale.
No full textIl ciclo sessuale della demospongia Geodia cydonium (Jameson, 1811): tre anni di osservazione mediante tecnica di marcatura individuale
No full textChoanocyte chambers in unreleased buds of Tethya seychellensis. (Wright) (Porifera, Demospongiae)
No full textThe buds of the sponge Tethya seychellensis, collected in May 2006 from South Male Atoll (Maldives), have been processed for histological and ultrastructural investigations. Buds show three stages, different in morphology and size, reflecting different steps of their differentiation: round-shaped buds (stage I), cylindrical-shaped buds (II) and thin-stalked spear-shaped buds (III). Cells with inclusions, belonging to the category of spherulous cells, are the main components of these buds. At stage I, some irregularly shaped cells, probably precursors of the choanocytes, are able to engulf and remove portions of the collagen matrix, a feature which could be interpreted as an initial step in choanocyte differentiation. Tethya seychellensis stands out among the other congeneric species owing to the occurrence of choanocyte chambers in the unreleased buds, as observed at stages II and III. The precocious differentiation of the choanocyte chambers allows the detached bud to act as a young functional sponge, thus enhancing the survival chances of these filter-feeding organisms. The structure of the buds of T. seychellensis stresses once more that in the genus Tethya the organisation of the buds represents a species-specific process, which varies according to the plasticity and the morphogenetic potentiality expressed by a single species
Association of the sponge Tethya orphei (Porifera, Demospongiae) with filamentous cyanobacteria
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Sperm ultrastructure and spermiogenesis in two Exogone species (Polychaeta, Syllidae, Exogoninae)
Full text linkThe spermatozoa of Exogone naidina and E. dispar are characterized by a prominent bell-shaped acrosome, a spheroidal nucleus, and a conventional flagellum. During spermiogenesis, the acrosomal vesicle undergoes conspicuous modifications leading to its final bell shape with a posterior opening. The subacrosomal material initially shows radiating filaments but in mature sperms it appears as a meshwork of electron-opaque material. The acrosomal axis is oblique with respect to the main longitudinal sperm axis. The chromatin is arranged in electronopaque strands in the early spermatids, then becomes amorphous, and is finally organized in filaments in mature sperms. Centrioles are orthogonally arranged beneath the nucleus and fibers radiate from the distal centriole to contact the plasma membrane and the single mitochondrion. The latter is located eccentrically on the side of the nucleus opposite the acrosome. A disk-shaped structure is evident beneath the distal centriole. The flagellar axoneme has a 9+2 microtubule pattern. A conspicuous glycocalyx surrounds the flagellar plasma membrane, and an electron-lucent space is present between these two structures at the distal tip of the flagellum. We compare the sperm morphology of these two species of Exogone with that described in other members of the subfamily Exogoninae. The fine structure of these two species supports the occurrence of an ent-aquasperm type within Exogoninae, in accordance with the brood strategy present within this subfamily. The mode of reproduction is of taxonomic importance for defining subfamilies within Syllidae, and is likely also of phylogenetic significance. Because epitoky is probably plesiomorphic, the ent-aquasperm type found in Exogoninae can be considered a derived feature within Syllidae
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