Rhabdotubus, a Middle Cambrian rhabdopleurid hemichordate |
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Authors: | STEFAN BENGTSON ADAM URBANEK |
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Affiliation: | Stefan Bengtson, Institute of Palaeontology, Box 558, S-751 22 Uppsala, Sweden;Adam Urbanek, Zaklad Paleobiologii PAN, Unit for Graptolite Research, Ul. Newelska 6, PL-01–447 Warszawa, Poland |
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Abstract: | Rhabdotubus johanssoni n.gen., n.sp., is described from the early Middle Cambrian Eccaparadoxides pinus Zone of Närke, southern Sweden. The colonies encrusted shells of inarticulate brachiopods, and occasionally trilobites, on otherwise soft substrates. The tubarium consists of repent and erect tubes. The former branch irregularly and produce a thecorhiza-like structure; the latter are erect and mostly isolated, up to 10 mm in length and widening gradually to about 1 mm width. Both repent and erect tubes are composed of fusellar bands, mostly irregularly arranged. Branching of repent tubes takes place through resorption or perforation of fusellar tissue in the parent tube. Branching of erect tubes occurs sporadically. There is no thecal dimorphism. No sclerotized stolon is present. Rhabdotubus is interpreted as the earnest known rhabdopleurid (Class Pterobranchia, Phylum Hemichordata). In general habitus it is similar to sessile graptolites of the Order Tuboidea. These similarities may well have phylogenetic significance, but further knowledge of the Tuboidea and other sessile orders of the Graptolithina is required to clarify the early evolution of graptolites. |
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Keywords: | Hemichordata Pterobranchia Rhabdopleurida Graptolithina Rhabdotubus morphology evolution Sweden Middle Cambrian |
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