 |
 |
 |
| Class Graptolithoidea, Order Rhabdopleuroidea, Family Uncertain Rhabdotubus johanssoni Bengtson & Urbanek, 1986 |
 |
| Fragments of erect zooidal tubes. of Rhabdotubus johanssoni. Above, primary adhesion and later divergence (dv) of two adjacent tubus (t). To the right is a fragment of the tube in transmitted light. |
| Rhabdotubus johanssoni is regarded as the earliest known pterobranch. It was described from the early Middle Cambrian Eccaparadoxides pinus Zone of Närke, southern Sweden, by Stefan Bengtson and Adam Urbanek, and named in honour of its discoverer, Mr. Jan Johansson of Sköllersta, Sweden. Bengtson & Urbanek (1986:293) wrote: "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 long in length and widening gradually to about 1 mm width. Both erect and repent 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." |
| The earliest known pterobranch hemichordate ! A number of similarities between this rhabdopleurid and the Tuboidea, an order of sessile graptolites, may indicate a close phylogenetic relationship between Rhabdotubus and tuboid graptolites. |
| BIBLIOGRAPHY Bengtson, A. & Urbanek, A. 1986. Rhabdotubus, a Middle Cambrian rhabdopleurid hemichordate. - Lethaia 19, 293-308. Urbanek, A., Mierzejewski, P. & Bengtson, S. 1992. Fine structure of the earliest known rhabdopleurid. - Lethaia, 25, 349-350. |
EDITORS: Piotr Mierzejewski, the Count of Calmont & Countess Maja Anna Korwin-Kossakowska Goethe Lab - Centrum Paleobiologii 2003-2006 |
 |
 |
 |
|
 |
 |