Patterns of Early Colony Development (Astogeny) in Four Genera of Trepostome Bryozoans from the Upper Ordovician
2011
Abstract The early astogeny of specimens representing the bryozoan genera Dekayia, Parvohallopora, Heterotrypa, and Homotrypella follows the same pattern documented in other Ordovician trepostomes. After larval settlement and metamorphosis, typically three primary, periancestrular, autozooids bud distally from the founder zooid, the ancestrula, with secondary zooids budding from the primaries, tertiary zooids from the secondaries, and so on. Progressive lateral displacement of buds, through backbudding, eventually produces a sub-circular ancestrular disk. Significant intergeneric differences in this basic pattern do not appear to exist. Intrageneric variability in budding pattern occurs during colony development. That variability might have resulted from any or all of the following sources: within-genus plasticity, the development of multiple ancestrulae, or environmental variation. The basic pattern of three primary buds developed from individual ancestrulae has been recognized in other trepostomes, some...
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