Koremagraptus obscurus, Rickards, R. B., Chapman, A. J., Wright, A. J. & Packham, G. H, 2003

Rickards, R. B., Chapman, A. J., Wright, A. J. & Packham, G. H, 2003, Dendroid and Tuboid Graptolites from the Llandovery (Silurian) of the Four Mile Creek Area, New South Wales, Records of the Australian Museum 55 (3), pp. 305-330 : 327

Koremagraptus obscurus n.sp.

Figs. 21A, 22C

Material. HOLOTYPE AM F114745 , the only specimen, from BF28, W tributary of Bridge Creek .

Diagnosis. Koremagraptus with growth direction of individual stipes difficult to ascertain due to complex and rapid anastomosis; most thecal apertures, with a diameter of 0.15 mm, are located on stipe walls and only rarely isolated.

Derivation of name. Reflecting the complex anastomosis of stipes.

Description. The large fragment of rhabdosome exhibits a complex mass of anastomosing stipes. Each stipe is clearly composed of numerous thecal tubes. Most thecal apertures are located on the stipe walls and only rarely are isolated. In Fig. 22C the arrows indicate the growth directions of three stipes. It is immediately obvious that in a distance of only 3 mm several instances of complex anastomosis occur. Most anastomosis seems to involve the transfer from one stipe to another of whole bundles of tubes. The tube apertures—presumed autothecal apertures—have a diameter of 0.15 mm. There is a suggestion that the stipes and thecal tubes are thin walled.

holotype, BF28; D, Koremagraptus elegantulus n.sp. AM F114752 , holotype, W885; E, Reticulograptus thomasi n.sp. AM F114756 , holotype, BF28. Scale bars 1 mm.

Remarks. Koremagraptus obscurus n.sp. has the characteristics of previously-described koremagraptids but taken to extremes in that the growth direction of individual stipes is difficult to ascertain at any one point, so great is the anastomosis. Koremagraptus obscurus can be contrasted, for example, with K. elegantulus n.sp., which is a more typical koremagraptid in its stipe arrangement. It is possible that other fragments in our collections might be referable to K. obscurus because small pieces of complex, thin-walled stipe fragments are not uncommon. Koremagraptus flexuosus Bouěek, 1957 from the basal Devonian has a similar stipe pattern but is less densely connected.

Figures

Fig.22.A,B. Thallograptus christoffersonae n.sp.: A,AM F114765, stipe development from basal holdfast, BF14 and B,AM F114746, holotype, F14; C, Koremagraptus obscurus n.sp. AM F114745,