Maldybulakia angusi, Edgecombe, 1998

Edgecombe, Gregory D., 1998, Early myriapodous arthropods from Australia: Maldybulakia from the Devonian of New South Wales, Records of the Australian Museum 50 (3), pp. 293-313 : 305-310

publication ID	https://doi.org/ 10.3853/j.0067-1975.50.1998.1288
DOI	https://doi.org/10.5281/zenodo.4658242
persistent identifier	https://treatment.plazi.org/id/03FE7A7C-2D46-FFAF-FA0B-FE53FE417B1E
treatment provided by	Felipe
scientific name	Maldybulakia angusi
status	sp. nov.

Treatment

Maldybulakia angusi n.sp.

Figs. 9 View Figure 9 -12

Maldybulakia new species 2 Edgecombe, 1998: fig. 2.

Etymology. For Angus Young.

Diagnosis. Maldybulakia with considerable serial variation in B-pleurotergites; posteromedian spine present on some tergites of anterior and posterior trunk tagmata; very long, posterolaterally-directed paratergal spines on most bilobate trunk pleurotergites; caudal tergite bearing long median spine; many tergites bearing robust tuberculation.

Types. HOLOTYPE trunk pleurotergite (B-pleurotergite) AM F.102565 (Fig. lOa); length 24.6 mm. Sugarloaf Creek Formation (Lochkovian or Pragian), near Three Oaks , Taemas district , New South Wales (35°04'S 148°5l'E). PARATYPES AM F.l02557-102564, 102566-102580, from type locality .

Description. T-tergites ( Fig. 9 View Figure 9 a-h) with length 32-39 percent of width. Anterior part of prozonite a flattened, boomerang-shaped surface that slopes forwards and lengthens medially to about 50 percent the length of the prozonite; rear edge of this surface forms a crest-like rise above posteriorpart of prozonite; well preserved specimens show dense, scaly sculpture ( Fig. 9c View Figure 9 ). Posterior part of prozonite with pair of moderately wide longitudinal furrows varying from faint to distinctly incised. Stricture moderately deep, gently convex forward medially, recurved distally around elliptical or teardrop shaped lateral lobes. Metazonite 70-86 percent length of prozonite. Posteromedian spine absent or short. Posterior margin approximately transverse between lobate processes which vary from broad and rounded to angular to short, slender spines. Tuberculation usually strong, rarely faint, sometimes more prominent on prozonite than on metazonite. Doublure ( Fig. 9a View Figure 9 ) as described for M. malcolmi .

Ring tergite ( Fig. 9i View Figure 9 ) as for M. malcolmi .

B-pleurotergites up to 24.6 mm in length. Anteriormost B-pleurotergite (Fig. lOb,f,h,i) distinguished by relatively short, wide proportions and short, knob-like projections at anterolateral edge of prozonite as seen in this pleurotergite only in M. malcolmi . Prozonite about 25 percent length of tergite, with cuticular sculpture of dense polygonal depressions amidst a network of low ridges (Fig. lOi). Lateral lobes of metazonite teardrop shaped, outer margin rounded, strongly inflated, with steep lateral and anterior edges encircled by well-impressed furrow. Posteromedian spine on median lobe of metazonite short, conical, and posterodorsally directed or absent. Paratergal spines long, strongly divergent (directed back 40-50 degrees from transverse line), largest known specimen 88 mm wide across spines (extrapolated from one half); inferred width across spines up to approximately 115 mm (based on size relative to largest known B-pleurotergites); dorsal and

ventral surfaces of spine bisected by shallow furrow along all but proximalmost part. Small and moderate sized tubercles abundant on lateral and median lobes of metazonite, somewhat stronger on lateral lobes.

B-pleurotergite of uncertain position (Fig. lOe,g) with short, posterolaterally directed paratergal spines. Prozonite relatively elongate, about 35 percent length of tergite. Short anterolaterally-directed, conical process at anterolateral corner of metazonite. Posteromedian spine on median lobe of metazonite varying from absent (Fig. 109) to strong (Fig. lOe), variably more posteriorly- or dorsally-directed. Tubercles on lateral lobes of metazonite faint to moderately strong; tubercles weaker on median lobe, sometimes obscure.

B-pleurotergites (probably second or third) from middle of tagma (Fig. lOa,c,d) with prozonite about 25 percent length of tergite. Anterolateral corner of pleurotergite extended as a short angulation that gently rises distally. Robust tubercles usually present, abundant on lateral and median lobes of metazonite. Polygonal sculpture grading into transversely elongate, scaly sculpture along anterior margin of prozonite and posterior margin of metazonite and fine tubercles on paratergal spines. Lateral lobes relatively longer than on first B-pleurotergite, less inflated. Paratergal spine long, more posteriorly directed than that on first B-pleurotergite, nearly straight or gently curved for much of length, with slightly stronger posterior curvature distally; spine flattened proximally, more rounded near tip; rounded, ventrally directed process on posterior margin at base of paratergal spine.

Posteriormost B-pleurotergite (Fig. lla,b,e) with prozonite up to 35 percent length of tergite. Anterolateral corner of metazonite forming a blunt, gently swollen angulation, separated from lateral lobe by shallow furrow. Median lobe relatively narrow, raised central part set off by pair of shallow longitudinal furrows. Tuberculation of median and lateral lobes subdued in most specimens. Paratergal spine long, approximately straight, weakly directed inwards, markedly flattened in section along entire length; longitudinal furrow on dorsal and ventral surfaces of spine deeper than on other pleurotergites, narrow but well-incised; spines with sculpture of small, crowded tubercles.

Caudal pleurotergite (Fig. lld,?f,g,h) with teardrop shaped or subtriangular lateral lobes; lobes substantially inflated, tuberculate, set off from median lobe by furrows of similar depth to or shallower than those on other Bpleurotergites; outer edge of lateral lobes steep, set off from more gently sloping outer border by shallow furrow. Lateral margin strongly convex outward. Median spine gently upturned, of about even width along entire known length, bisected by shallow longitudinal furrow.

Telson sclerites unknown.

Discussion.AlthoughMaldybulakia angusi is distinguished from its congenerics by numerous autapomorphies, a separate genus cannot be upheld unless reasonable synapomorphies are identified for M. malcolmi and M. mirabilis . As noted above, most of the similarities between the latter pair of species are probably symplesiomorphies

and, if so, restricting Maldybulakia to these two species would recognise a paraphyletic group. In fact, certain characters might instead serve to unite the two Australian species to the exclusion of M. mirabilis . The flattened, sloping anterior scarp on the prozonite of the T-tergite is a distinctive modification shared by these two species but appears less developed in M. mirabilis ( Tesakov & Alekseev, 1992: fig. Ig).

Considerable variability is observed in the strength of tuberculation on T-tergites as well as B-pleurotergites in M. angusi . Some specimens have only weak expression of tubercles ( Figs. 9b View Figure 9 , lOe, lIe), whereas most show them to be more distinct or pronounced. Because of continuous gradation in tuberculation in otherwise similar tergites this is not regarded as an important criterion for distinguishing different pleurotergites. Presence or absence of a median spine on the metazonite is a feature that varies between tergites that are otherwise similar. This is observed on the T-tergites (compare Fig. 9b and 9g View Figure 9 ) as well as on various Btergites that appear to represent the same position (e.g., Fig. lOb versus lOh; Fig. lOe versus 109). Presence or absence of a median spine is considered to vary between individuals.

The antero-posterior position of B-pleurotergites can be largely determined based on the progressively more posterior direction of the paratergal spines on posterior segments (as observed analogously in other spiny myriapods, such as euphoberiid diplopods). Consistent with this line of evidence are other correspondences with known positions in M. malcolmi : the anterior pleurotergites are shorter relative to their width, and the anteriormost Bpleurotergite is distinguished by its anterolateral processes on the prozonite (Figs. lOf, 12c; compare with Fig. 6d View Figure 6 ). The posteriormost B-pleurotergite (immediately anterior to the caudal pleurotergite) is identified by its posteriorlydirected paratergal spines and relatively long median lobe on the metazonite ( Figs. 11a,b,e View Figure 11 , 12f).

Given the above considerations, the minimal number of sclerites in the trunk of Maldybulakia angusi is depicted in Fig. 12. The B-pleurotergites can be sorted into four morphological groups (Fig. 12c-f)' excluding the caudal pleurotergite (Fig. 12g), thus allowing that the number of pleurotergites may be identical to that in M. malcolmi and, apparently, M. mirabilis . The position of the Bpleurotergite reconstructed in Fig. 12d is uncertain, constrained only by the likelihood that those shown in Figs. 12c and 12f are the first and last in the series based on their morphological correspondences to M. malcolmi . The specimen in Fig. 11f View Figure 11 conforms to a caudal pleurotergite except for the absence of a median spine, although this is possibly due to breakage. Its lensoid outline (i.e., absence of paratergal spines) with tightly curved lateral margins is similar to caudal pleurotergites that have a median spine ( Fig. 11g View Figure 11 ). In M. malcolmi , this specimen is most comparable to a lensoid specimen regarded as a caudal pleurotergite (Fig. 5c).

The best preserved external moulds display a cuticular sculpture of dense polygonal depressions amidst a maze of low ridges (Fig. lOi), as is also seen in M. malcolmi (Fig. 5j,k) and M. mirabilis ( Tesakov & Alekseev, 1992: fig. 1i). This character is, accordingly, general for Maldybulakia .