Stelletta grubii is an oviparous demosponge, which, during its reproductive period from summer to autumn, has small eggs (80-90 microns) dispersed uniformly in the mesohyl. The nucleolated nucleus is surrounded by dictyosomes containing small vesicles, which contribute to form reserve material. Vesicles, numerous food vacuoles, and groups of mitochondria are observed in the granular cytoplasm. Electron-dense yolk inclusions and lipids are found peripherally. The cortical portion of the egg cytoplasm possesses vacuoles with fibrillar contents. The egg forms pseudopodia, which could permit the capture of numerous bacteria present in the surrounding mesohyl. A thick layer of collagen fibrils, including lophocytes, separates the egg from the surrounding sponge mesohyl. Ultrastructural analysis has demonstrated the presence both of cellular components capable of autosynthetic activity (nutrient vesicles) and of phagocytosis mechanisms (pseudopod capture of bacteria) for the storage of nutrients by the egg.

The budding process has been studied in two congeneric Mediterranean species belonging to Tethya from different sampling sites: Marsala and Venice Lagoons (Tethya citrina); Marsala Lagoon and Porto Cesareo Basin (Tethya aurantium). Buds, connected to the adult by a spiculated stalk, differ between the two species in morphology and size, since those of T. citrina are small with elongated bodies, showing only a few spicules protruding from the apical region, whereas those of T. aurantium are round, larger, and show spicules radiating from the peripheral border. In T. citrina, cells with inclusions, varying in electron density and size, represent the main cell types of the buds. In T. aurantium, the cell component shows a major diversification, resulting from spherulous cells, grey cells, vacuolar cells and peculiar micro-vesicle cells. Neither canals nor choanocyte chambers were observed in the buds of the two species. In T. citrina, bud production is similar in both sampling sites. In T. aurantium, budding occurs more rarely in Porto Cesareo Basin, probably in relation with environmental factors, such as the covering of the cortex by sediment and micro-algae. Finally, in the buds of both species, the spicule size does not differ from that of the cortex of the adult sponges, further supporting the main involvement of the cortex in organizing the skeletal architecture of the buds.

Abstract. This histochemical and ultrastructural study describes the epidermal gland cells of a tubicolous polychaete, Branchiomma luctuosum. The histochemistry was carried out using standard techniques and FITC‐labelled lectins. Four types of secretory cells were identified in two categories: orthochromatic cells (Type 1) and metachromatic cells (Types 2, 3, and 4). The secretory product of the Type‐1 orthochromatic cells contains neutral glycoproteins with Galβ1,3GalNAc residues. Metachromatic cells produce acidic, mainly sulfated, glycoconjugates with Galβ1,3GalNAc residues (Type 2) or glucosidic and/or mannosidic residues (Types 3 and 4). In sialylated chains, terminal sialic acid is bound to the penultimate GalNAc and Galβ1,3GalNAc residues. The complex composition of the mucus produced by epidermal gland cells of B. luctuosum may be correlated with its different functions. Ultrastructural studies of the epidermal gland cells showed differing morphology, and the presence in the gland cells of Types 3 and 4 of a funnel‐shaped structure for the extrusion of the secretory material.

The sexual reproductive cycle of the Tetractinomorpha Spirophorida Cinachyra tarentina was studied mainly using light microscopy on samples collected in South Italy over a 2-year period. Some aspects of the egg morphology were observed using transmission electron microscopy. Each year, young oocytes in previtellogenesis appeared in May and coexisted with growing oocytes. Yolk-filled eggs were present in June and July. Oogenesis preceded spermatogenesis which occurred only in June. Cinachyra tarentina is an oviparous species having small eggs ranging from 40 to 50 pm in diameter which are scattered in the mesohyl and have a nucleolated nucleus surrounded by dictyosomes of the Golgi apparatus. Growing oocytes and yolk-filled eggs have an irregular surface because of the presence of numerous pseudopodia which protrude into the mesohyl. Even though apparently gonochoric individuals were mostly observed, the rare specimens with sperm clusters and young oocytes proved the occurrence of successive hermaphroditism as an underlying mechanism. Some aspects of the reproductive biology of C. tarentina are compared with that of other Tetractinomorpha.

The 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 spearshaped 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.