Abstract

Serial peels through primary zones of astogenetic change of four taxa designated on external features to be phylloporinid bryozoans demonstrate that three of these taxa have early growth stages generally similar to those of trepostomes and cyclostomes, which are "typical" for stenolaemate bryozoans. Similarities include the tubular shapes of the first formed zooid (the ancestrula) and other basal zooids, the presence of a reflection and change in growth direction from distal to proximal of the upper portions of the conical outer wall that initially covered the ancestrula, and the way in which all basal zooids grew along the substrate for at least part of their length. Differences from "typical" stenolaemates include the relatively small number of zooids in the phylloporinid bases and, in some, the lack of basal zooids proximal to the ancestrula. The fourth supposed phylloporinid taxon has early growth stages in some aspects similar to those of fenestrate bryozoans: an ancestrula with a vertical axis of symmetry is surrounded by a sequentially budded, curvilinear series of basal zooids. The shapes of the ancestrula and other basal zooids differ from known fenestrate basal zooids in that they are squat cylinders rather than hemispheres topped by a short, narrow tube. Because of the two fundamentally different types of early growth exhibited in the four taxa studied, it is suggested that recognition of phylloporinids based on external features has produced a polyphyletic grouping. Although primary zones of astogenetic change cannot form the sole basis for taxonomic placement or interpretation of evolutionary relationships, the pronounced difference between those of known fenestrates and three of the four phylloporinids described herein, suggests that there is greater distance between them and most fenestrates than between them and more typical stenolaemates.--Modified journal abstract.

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