A light- and electron-microscopic investigation of gametogenesis in Typosyllis pulchra (Berkeley and Berkeley) (polychaeta: Syllidae)

Abstract

Tryposyllis pulchra reproduces by the production of three to four gamete-bearing stolons (schizogamy) during consecutive 30--day periods. Although gonads are found in a large number of segments, only those in the posterior-most segments produce gametes and become incorporated into the developing stolon. The more anterior gonads remain undifferentiated and probably sexually undetermined until they are needed in future stolonizations. Gonial cells, which will eventually become either male or female, are ultrastructurally identical at the onset of each stolonization period. Spermatogenesis is marked by a short proliferative period followed by differentiation and spermiogenesis. The first ultrastructural signs of spermatogenesis were found in coelomic spermatogonia on day 10 of stolon formation. Spermatogonia are joined by intercellular bridges, which are maintained until the early spermatid stage. Synaptonemal complexes mark the onset of meiosis, which is apparently synchronized in the syncytial clusters of primary spermatocytes. Spermiogenesis occurs during the final 10 days of stonolization and a variety of stages is present within a single animal. All sperm mature by the time the stolon detaches. Acrosome formation and nuclear condensation are described in addition to the ultrastructure of mature sperm.

Oogenesis and oocytes

“…In Hydroides spp. (Colwin & Colwin, 1961), Pomatoceros triqueter (Ap Gwynn & Jones, 1971), Typosyllis pulchra (Heacox & Schroeder, 1981) Terebella rubra (Eckelbarger, 1984), Sabellaria alveolata (Pasteels, 1965a, b;Franklin, 1966), Phragmatopoma lapidosa (Eckelbarger, 1979), and Marenzelleria viridis (Bochert, 1996), the microvilli terminate in a monolayer of surface granules. These granules attain their greatest complexity in the Sabellariidae (Fig.…”

“…Nurse cell-oocyte associations in polychaetes are relatively rare and they occur sporadically, even within closely related species (Rouse, 1992). They have been described within the Phyllodocida in the syllid Typosyllis pulchra in which groups of nurse cells surround individual oocytes (Heacox & Schroeder, 1981), in some exogonine syllids in which nurse cells, oocytes, and follicle cells are associated (Cognetti-Varriale, 1965), and in the tomopterid Tomopteris helgolandica (Å kesson, 1962) where a cluster of seven nurse cells is attached to one end of the oocyte (Figs. 1C; 9B).…”

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

“…In fact, the sperm ultrastructure of S. vittata resembles the typical ect-aquasperm already observed in S. krohni, S. pigmentata and Syllis sp. (Heacox and Schroeder 1981;Jamieson and Rouse 1989;Lepore et al 2006), and the herein analyzed S. prolifera and S. gerlachi.…”

“…In any case, the ultrastructural differences between S. gerlachi and S. prolifera herein observed reinforce the Heacox and Schroeder 1981) and f Syllis krohni (redrawn after Lepore et al 2006). a acrosome, ss sub-acrosomal space, n nucleus, pm plasma membrane, m mitochondrion, pc proximal centriole, dc distal centriole critics (Aguado et al 2007) to the previous phylogenetic reconstruction based on morphology, considering the two species as closely related in the prolifera-complex (Licher 1999).…”

“…(as Typosyllis sp. ), S. pigmentata (Chamberlin, 1919) (as Typosyllis pulchra) and S. krohni Ehlers, 1864 (Heacox and Schroeder 1981;Jamieson and Rouse 1989;Lepore et al 2006). In contrast, the study of sperm ultrastructure and its correlation with reproductive biology may be useful for the reconstruction of the phylogenetic patterns within Syllidae (Franke 1999;Giangrande et al 2002).…”