Stelechocladia praeattenuata, 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 : 322

Stelechocladia praeattenuata n.sp.

Figs. 17B , 19A,B

Material. HOLOTYPE AM F114743 a-b, from BF28, W tributary of Bridge Creek . PARATYPES AM F114765 from BF14, Bridge Creek ; AM F114781 from F14, Bridge Creek ; AM F114782 a-b from BF18 ; AM F114783 from F19, Four Mile Creek ; and AM F114784 from BF18 .

Derivation of name. To reflect its earlier occurrence than the most similar species, Stelechocladia attenuata Bouěek, 1957 .

Diagnosis. Robust Stelechocladia with dominant main stipes and shorter, intermediate, finer stipes quite regularly arranged; 10–14 stipes in 10 mm; autothecal spacing 30– 40 in 10 mm; rhabdosome developed from broad holdfast; stipes with proximal lateral width of 1.0 mm at most; dorsoventral width 0.70–0.90 mm.

Description. The rhabdosome develops from a holdfast 3– 5 mm across; although detailed growth close to the holdfast is not clear, three or four main stipes seemingly arising from an amorphous mass of tissue. The mains stipes are initially up to 1 mm wide (lateral width) though usually less than this. More distally they gradually become narrower reaching 0.25–0.30 mm. Intermediate stipes are similarly tapered. However, when seen in profile view, when the denticulate autothecae are clearly visible, the dorsoventral width is fairly constant at 0.70–0.90 mm. Branching from the main stipes is frequent but irregular, and it tends to be from one side of the main stipe. Branching from the main stipes takes place every 0.50–1.50 mm. The result of the branching is a striking array of spike-like stipes, quite unconnected (except at the branching points) with shorter, intermediate stipes filling the spaces between main stipes. Many intermediate stipes are rather short and seem to be positioned merely to fill a space between two adjacent but distally converging longer stipes. No bithecae have been detected.

Remarks. Stelechocladia attenuata from the Přídolí of the Czech Republic is undoubtedly the closest species but is much larger and altogether more robust than in S. praeattenuata , and also has a wider autothecal spacing (25 in 10 mm compared with 30–40 in 10 mm: see Kraft, 1984).

Figures

Fig. 17. A, Callograptus ulahensis n.sp., AM F114760, holotype, BF15; B, Stelechocladia praeattenuata n.sp.,AM F114743, holotype, BF28; C,D, Acanthograptus praedeckeri praedeckeri n.sp., respectivelyAM F114792, holotype, BF28 and AM F114568a, F14. Scale bars 1 mm.

Fig. 19. A,B, Stelechocladia praeattenuata n.sp.: A, AM F114743, holotype, and B, AM F114744, both BF18; C, Acanthograptus praedeckeri praedeckeri n.sp., AM F114629a, F14. Scale bars 1 mm.