Cellular details of early embryogenesis have been studied extensively among cyclophyllidean cestodes, but have been reported for only 2 species of the order Proteocephalidea, both belonging to the genus Proteocephalus. Thus, we performed a detailed ultrastructural analysis of early embryos of a second species, Corallobothrium fimbriatum, including early events in the formation of the embryonic envelopes. Adult worms were collected from the small intestine of brown bullhead catfish, Ameiurus nebulosus, from the St. Lawrence River in North America and processed by standard methods for transmission electron microscopy. The vitelline capsule consists of 2 closely apposed electron-dense membranous layers, separated by a more electron-lucent material. The 2 vitellocytes that accompany each oocyte contain numerous ribosomes, vesicles, and lipid droplets. These fuse to form a vitelline syncytium, which elongates and almost completely encircles the cleaving embryo by the 4-blastomere stage, forming a partial lipid-rich cellular envelope that undergoes apoptosis as cleavage continues. This envelope is later replaced by outer and inner embryonic envelopes. The outer envelope derives from the fusion of the vitelline syncytium with the cytoplasm of macromeres, whereas the inner envelope originates from 3 mesomeres. Simultaneous to the formation of the embryonic envelopes, other blastomeres multiply and differentiate, while some micromeres undergo degeneration or apoptosis. In most respects, ultrastructural features of early C. fimbriatum embryos closely resemble those of previously studied Proteocephalus longicollis, but differ somewhat from those of other orders. This demonstrates that, despite marked ultrastructural heterogeneity within some orders such as the Cyclophyllidea, some embryonic traits distinguish cestode orders from each other.
You have requested a machine translation of selected content from our databases. This functionality is provided solely for your convenience and is in no way intended to replace human translation. Neither BioOne nor the owners and publishers of the content make, and they explicitly disclaim, any express or implied representations or warranties of any kind, including, without limitation, representations and warranties as to the functionality of the translation feature or the accuracy or completeness of the translations.
Translations are not retained in our system. Your use of this feature and the translations is subject to all use restrictions contained in the Terms and Conditions of Use of the BioOne website.
Vol. 96 • No. 5