| Popis: |
The post-larval development of the reproductive system in Nassarius vibex was investigated using a histological approach, to establish the sequence of organogenesis and the contribution of different organogenetic components to the adult system. This research is part of a broader investigation with two primary objectives. The first is to provide a detailed analysis of reproductive system development that can be used to re-evaluate existing character sets and generate new characters for reconstructing gastropod phylogenies. The reproductive tract has always been a promising but problematic system to work with in phylogenetic research, because of the uncertain homology of many parts of the system. Most of the reproductive system itself develops during post-larval ontogeny, a phase of gastropod development that has been investigated in very few taxa; thus this line of research has the potential to provide a wealth of new information. The second objective is to establish comparable organogenetic series for representative gastropod taxa that can be used to investigate the significance of heterochronic processes in the evolution of gastropod organ systems. The reproductive system in Nassarius vibex develops very late in ontogeny from two ontogenetic components in the male and three in the female. Development and differentiation of the organ system is not completed until near maturity. In both sexes, ductal components develop first and fuse to form the rudimentary reproductive tract. Gonads and accessory reproductive structures develop after the ductal components are fused, and glandular tissues do not appear until near maturity. The penis does not develop until near maturity. The capsule and albumen glands in this species are broadly conjoined, unlike the situation in other members of Nassarius. The ingesting gland develops between them as a dorsal outgrowth of the glandular lumen. |
