The suggestion has been made by Allmann and recently upheld by Schepotieff that Rhabdopleura is related to some of the Graptolites.
553; " Rhabdopleura and Graptolites," Neues Jahrb.
Since no graptolites are known living, or, indeed, since palaeozoic times, the interpretation of their structure and affinities must of necessity be extremely conjectural, and it is by no means certain that they are Hydrozoa at all.
See the treatise of Delage and Herouard (Hydrozoa, ), and the article Graptolites.
In the Maecuru, another northern affluent, graptolites of Ordovician age have been discovered, and Silurian fossils are said to have been found in the Maraca.