Acanthograptus praedeckeri minimus, 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 : 324-325

Acanthograptus praedeckeri minimus n.subsp.

Fig. 20F

Holotype. AM F114630 , from F6, Wallace Creek .

Derivation of name. To indicate smaller dimensions than the nominate subspecies.

Diagnosis. Acanthograptus praedeckeri differing from the nominate subspecies in: its much smaller form with narrower stipes, the more open “space coverage” by the branching, and with twig spacing twice as frequent.

Description. The single well-preserved rhabdosome shows several well-developed branches and numbers of twigs. The stipes are uniformly narrow at 0.20 mm yet clearly compound with bundles of long narrow tubes. It is possible that some of the twigs may terminate with a single autotheca but parts of some twigs have more than one thecal tube involved. Some thecae appear to open on the main stipes, their apertures adpressed to the surface. Twigs are 0.30– 0.60 mm long, usually directed at about 45° to the stipe axis; twig spacing more than 20 in 10 mm.

Remarks. Although having the same general appearance as the type subspecies, A. p. minimus is a much smaller form with narrower stipes and the “space coverage” by the branching is more open. It is difficult to give a twig spacing accurately, because of the numbers of branches, but twig spacing is certainly twice as frequent as in the type subspecies.

Figures

Fig. 20. A–E, Acanthograptus praedeckeri praedeckeri n.subsp., respectively AM F114568, AM F114568, AM F114741,AM F114742 and AM F114740, all from F14; F, Acanthograptus praedeckeri minimus n.subsp.,AM F114630, F6. Scale bars 1 mm.