Titlebook: Receptaculitids; A Phylogenetic Debat Matthew H. Nitecki,Harry Mutvei,Doris V. Nitecki Book 1999 Springer Science+Business Media New York 1

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Summary and Beyond,s, and however strongly it may be wished, convergence and analogy in organisms of unknown relationships cannot be differentiated from homology and phylogeny. While many receptaculitid characters may appear to be homologous with structures in sponges or dasyclads, they may be structurally convergent.

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keloid

f phosphatized receptaculitids on the Baltic Sea island ofÖland, the authors conclude that receptaculitids possess anattribute not found in any other group of organisms, living or fossil.978-1-4613-7124-3978-1-4615-4691-7

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Geology,t receptaculitids may have been related to the Cambrian radiocyathids, however, Andrey Yu. Zhuravlev (1989) opposed this. Unless these relationships will be adequately proven, receptaculitids appear to have originated abruptly in the Early Ordovician, and their ancestry remains unknown.

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Morphology of a Merom,). Feet, when present, are parallel to the plates, and often reflect the rhombic shapes of the plates (fig. 5.2) or are triangular (fig. 5.3). Heads form the ectorhin, and feet the endorhin (Billings 1865a), but a two-walled structure forms only when feet are present. In . the shafts are thick and the heads and feet are massive (fig. 5.1)

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