Margherita Sciscioli

Investigation of the budding process in Tethya citrina and Tethya aurantium (Porifera, Demospongiae)

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.

Sexual reproduction of Cinachyra tarentina (porifera, demospongiae)

Abstract 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 pre‐vitellogenesis 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.

External gestation of Exogone naidina Öersted, 1845 (Polychaeta, Syllidae): ventral attachment of eggs and embryos

The external gestation of sexually ripe females of the species Exogone naidina (Polychaeta, Syllidae) is described by means of SEM and TEM analysis. The eggs, embryos and juveniles are attached in close vicinity of each parapodial complex in a position immediately below each ventral cirrus and are connected to the female by a cup like structure. The formation of this adhesive disk is linked to secretory cells scattered between dermal cells of ripe female. This adhesive disk is present only in sexually mature animals and is considered as epitokous structure. The evolutive significance of ventral and dorsal attachment found within the Exogoninae is also discussed.

Choanocyte chambers in unreleased buds of Tethya seychellensis (Wright, 1881) (Porifera, Demospongiae)

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 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.

Sperm ultrastructure of three Syllinae (Annelida, Phyllodocida) species with considerations on syllid phylogeny and Syllis vittata reproductive biology

Phylogeny of Syllidae is under debate due to new studies based on molecular and morphological data. The noticeable taxonomic diversity of syllids (about 700 listed species) is also mirrored in the array of reproductive strategies as well as in sperm morphology, counting a display of forms already supposed to reflect phylogenetic relationships between the species. The sperm ultrastructure of Syllis gerlachi, S. prolifera and S. vittata is herein presented and compared to the Syllinae species studied previously. Moreover, the egg structure and the gamete allocation within stolons of S. vittata are particularly investigated. Both male germinal cells at different level of maturation and oocytes were found in the same individual of S. vittata, suggesting simultaneous hermaphroditism. The ultrastructural analysis revealed that the observed spermatozoa belong to the ect-aquasperm type resembling those of the similar studied species (Syllis sp., S. pigmentata and S. krohni). Differences in the acrosome structure and nucleus shape are in accordance with a recent phylogenetic reconstruction and suggest a trend in the evolution of spermatozoa in Syllinae toward the development of the apical part. However, further molecular and ultrastructural analyses are needed to support this hypothesis. This is the first record of simultaneous hermaphroditism within Syllinae.

A study on spermatogenesis of three Mediterranean serpulid species

Abstract Sperm ultrastructure and some steps of spermatogenesis of the serpulids Hydroides dianthus, Serpula vermicularis and Vermiliopsis infundibulum are reported. In all the species examined the germinal cells originated from a germinative epithelium associated to blood vessels in the intersegmental septa. The spermatocytes were irregular in shape with a large nucleus and a thin cytoplasmic layer. In early spermatids in which the nucleus gradually condensed, a developed endoplasmic reticulum and some electron-dense bodies were observed. The nucleus was dehydrated in the late spermatids and assumed a cylindrical shape. In all the examined species, the morphology of the ripe spermatozoa can be ascribed to the ect-aquasperm type. The acrosome had a simple cup shape in V. infundibulum, whilst it was more developed extending laterally to the nucleus in H. dianthus, and cup-shaped with a swelling towards the nucleus in S. vermicularis. When the morphology of the serpulid spermatozoa was superimposed on a phylogenetic scheme, some trends could be highlighted. Although the paucity of data on serpulid spermatozoa ultrastructure at present prevents any phylogenetic inference, the comparison of acrosome ultrastructure within a group having similar reproductive strategies showed an increase in the internal complexity of the acrosome.

Some steps of spermatogenesis in Halichondria semitubulosa (Demospongiae, Halichondriidae)

Spermatogenesis of the marine sponge Halichondria semitubulosa (formerly Pellina semitubulosa) has been investigated at the ultrastructural level. This process can be observed in March when, among the choanocyte chambers of the aquiferous system, spermatic cysts are visible. They are delimited by pinacocyte‐like cells and include elements in progressive development: spermatocytes of the first and second order, spermatids and spermatozoa. The early phase of spermatogenesis was not detected. Spermatocytes of the first order show an elongated shape, several small mitochondria and patched chromatin; spermatocytes of the second order, frequently connected by bridges, show denser chromatin, a single large mitochondrion with numerous tightly adherent cristae, glycogen, and round‐shaped inclusions with a central electron‐dense core. In the spermatids the chromatin tends to be packed in the central region. Spermatozoa have a uniformly dense nucleus in close association with the large mitochondrion. Sperm maturation takes place synchronously within the same cyst but asynchronously within the same specimen.

Lectin histochemistry and ultrastructure of microgranular cells in Cinachyra tarentina (Porifera, Demospongiae)

A histochemical study is described that characterizes microgranular cells of the demosponge Cinachyra tarentina (C. tarentina) with the use of routine staining methods for mucosubstances, lectin histochemistry and electron microscopy. Microgranular cells are rare or absent in other species of sponges, but abundant in this species. Microgranular cells are present in both ectosome and mesohyl, particularly along the canal of the aquiferous system and around spicule holes. Inclusions of microgranular cells and the extracellular matrix were particularly positive for acidic glycoproteins with abundant sulfated ester groups and glycosidic residues containing GalNAc and Galbeta1,3GalNAc. Terminal L-fucose bound to the penultimate GalNAc residues and/or difucosylated oligosaccharides were present as well. Our results suggest that soybean lectin (SBA), peanut lectin (PNA), and winged pea lectin (WPA) are valuable markers for identifying microgranular cells of C. tarentina. Electron microscopy revealed some of the microgranular cells to contain small smooth cytoplasmic vesicles originating from the Golgi complex and few electron-dense granules, others were characterized by numerous secretory granules and vacuoles formed by vesicle fusion and connected with the plasma membrane. Our results suggest that microgranular cells in C. tarentina contribute to the synthesis of glycoprotein components of the extracellular matrix.

Ultrastructural organization of choanocyte chambers in the haplosclerid Pellina semitubulosa (Porifera, Demospongiae): A cue for water flow into the sponge body

Abstract The choanocyte chambers of the haplosclerid Pellina semitubulosa were investigated with regard to their ultrastructural architecture. They are separated from the mesohyl and contain central cells arranged to form a uniform layer. Their cytoplasmic extensions enter the distal parts of the choanocyte collars, thus enveloping the end of the microvilli. Central cells seal up all the spaces between choanocyte collars. On the basis of choanocyte chamber architecture, a water flow dynamics and related filter feeding activity is proposed, which supports a water passageway through the small microvillar slits into the interior of the collar. A slight detachment of the central cells from the microvillar ends originates spaces for a direct water flow into the chamber. Such a plastic organization might enhance the filtration efficiency and prevent chamber clogging as well.