The placental analogue and the pattern of sexual reproduction in the cheilostome bryozoan Bicellariella ciliata GymnolaemataReport as inadecuate

The placental analogue and the pattern of sexual reproduction in the cheilostome bryozoan Bicellariella ciliata Gymnolaemata - Download this document for free, or read online. Document in PDF available to download.

Frontiers in Zoology

, 9:29

First Online: 25 October 2012Received: 27 August 2012Accepted: 23 October 2012


BackgroundMatrotrophy or extraembryonic nutrition – transfer of nutrients from mother to embryo during gestation – is well known and thoroughly studied among vertebrates, but still poorly understood in invertebrates. The current paper focuses on the anatomy and ultrastructure of the oogenesis and placentotrophy as well as formation of the brood chamber ovicell in the cheilostome bryozoan Bicellariella ciliata Linnaeus, 1758. Our research aimed to combine these aspects of the sexual reproduction into an integral picture, highlighting the role of the primitive placenta-like system in the evolution of bryozoan reproductive patterns.

ResultsFollicular and nutrimentary provisioning of the oocyte occur during oogenesis. Small macrolecithal oocytes are produced, and embryos are nourished in the ovicell via a simple placental analogue embryophore. Every brooding episode is accompanied by the hypertrophy of the embryophore, which collapses after larval release. Nutrients are released and uptaken by exocytosis embryophore and endocytosis embryo. Embryos lack specialized area for nutrient uptake, which occurs through the whole epidermal surface. The volume increase between the ripe oocyte and the larva is ca. 10-fold.

ConclusionsThe ovicell is a complex organ not a special polymorph as often thought consisting of an ooecium protective capsule and an ooecial vesicle plugging the entrance to the brooding cavity that develop from the distal and the fertile zooid correspondingly. Combination of macrolecithal oogenesis and extraembryonic nutrition allows attributing B. ciliata to species with reproductive pattern IV. However, since its oocytes are small, this species represents a previously undescribed variant of this pattern, which appears to represent a transitional state from the insipient matrotrophy with large macrolecithal eggs to substantial one with small microlecithal ones. Altogether, our results substantially added and corrected the data obtained by the previous authors, providing a new insight in our understanding of the evolution of matrotrophy in invertebrates.

KeywordsMatrotrophy Oogenesis Ovicell Placental analogue Bicellariella ciliata Bryozoa Electronic supplementary materialThe online version of this article doi:10.1186-1742-9994-9-29 contains supplementary material, which is available to authorized users.

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Author: Martin Moosbrugger - Thomas Schwaha - Manfred G Walzl - Matthias Obst - Andrew N Ostrovsky


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