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A simplified placenta‐like system for the transport of extraembryonic nutrients during embryogenesis of Bugula neritina (bryozoa)
Author(s) -
Woollacott Robert M.,
Zimmer Russel L.
Publication year - 1975
Publication title -
journal of morphology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.652
H-Index - 74
eISSN - 1097-4687
pISSN - 0362-2525
DOI - 10.1002/jmor.1051470308
Subject(s) - biology , bryozoa , embryo , endoderm , anatomy , microbiology and biotechnology , epithelium , embryogenesis , ectoderm , embryonic stem cell , botany , genetics , taxonomy (biology) , gene
Embryos of the marine cheilo‐ctenostome bryozoan Bugula neritina undergo a marked increase in volume (about 500‐fold) during embryogenesis while being retained in a brood chamber. Previous morphological studies indicate that shortly after transfer of the zygote to the brood chamber, the epithelium of the maternally‐derived portion of the brood chamber, the ooecial vesicle, differentiates in regions adjacent to the embryonary space from a squamous to a columnar form suggesting that the parent is involved as a source of extraembryonic nutrients required for the extensive growth of the embryo. Results of the present ultrastructural study indicate that hypertrophy of the epithelial cells occurs only in that region of the ooecial vesicle which opposes the embryo, that differentiation (and subsequent regression) of the lining are predictable events correlated with the onset (and termination) of embryonic growth, and that hypertrophied cells are well equipped for the synthesis and transport of macromolecular materials across the vesicle wall to the developing embryo. Further, that portion of the embryo's ectoderm (the presumptive metasomal sac) in contact with this hypertrophied epithelium is morphologically specialized for the uptake of nutrients. Finally, shortly before release of the larva, this intimate association of the metasomal sac tissue and the hypertrophied ooecial vesicle lining epithelium is terminated by invagination of the sac and atrophy of the lining.