Miriam Gherardi

Inventory and distribution of hard bottom fauna from the marine protected area of Porto Cesareo (Ionian Sea): Porifera and Polychaeta

Abstract The hard bottom fauna of the marine protected area of Porto Cesareo (Salento Peninsula) was examined considering two representative benthic groups, Porifera and Polychaeta. Sampling was performed by SCUBA divers from the surface to a depth of 25 m in a variety of environments. Sponge and polychaete assemblages were rich and diversified, with a total of 160 taxa collected (66 and 94, respectively), representing the first large contribution to the knowledge of the two groups in the marine protected area. This was particularly true for polychaetes, 80% of which had not been previously reported in the literature for this area. The distribution of the species in the examined environments is also given.

Epibiontic and endobiontic polychaetes of Geodia cydonium (Porifera, Demospongiae) from the Mediterranean Sea

Polychaete assemblages associated to the sponge Geodia cydonium were investigated at two sampling sites in the Mediterranean Sea: Porto Cesareo Basin (Apulia) and Marsala Lagoon (Sicily), both characterized by sheltered hydrodynamic conditions. Samples were seasonally performed during 1997, in order to compare the assemblages coming from the two localities studied, considering separately the internal and external tissues of the sponge, and with the aim of evaluating the influence of sponge size on polychaete colonization. The examined sponge is characterized by a peculiar stratification of its tissues: an external thick and hard layer, the cortex, and an internal softer one, the choanosome. Statistical analysis showed that this was the main factor controlling polychaete assemblage, with the internal tissue, less rich and diversified, appearing impoverished with respect to the external layer. A similarity in species composition was observed between sites, even though some differences were evidenced in the abundance of some species, mainly reflecting differences in local environmental conditions. Species richness and density increased with the increasing sponge size. Such a situation is particularly evident at Porto Cesareo, where sponges are covered by an algal layer which is particularly rich on the largest specimens, thus suggesting that most of the species of polychaetes were linked more to the neighbouring environment than to the sponge itself.

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.

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.