A simplified placenta-like system for the transport of extraembryonic nutrients during embryogenesis ofBugula neritina (bryozoa)

摘要: Embryos of the marine cheilo-ctenostome bryozoan Bugula neritina undergo a marked increase in volume (about 500-fold) during embryogenesis while being retained brood chamber. Previous morphological studies indicate that shortly after transfer zygote to chamber, epithelium maternally-derived portion ooecial vesicle, differentiates regions adjacent embryonary space from squamous columnar form suggesting parent is involved as source extraembryonic nutrients required for extensive growth embryo. Results present ultrastructural study hypertrophy epithelial cells occurs only region vesicle which opposes embryo, differentiation (and subsequent regression) lining are predictable events correlated with onset termination) embryonic growth, and hypertrophied well equipped synthesis transport macromolecular materials across wall developing embryo. Further, embryo's ectoderm (the presumptive metasomal sac) contact this morphologically specialized uptake nutrients. Finally, before release larva, intimate association sac tissue terminated by invagination atrophy lining.