Myrmecina difficulta, Shattuck, Steve, 2009

Shattuck, Steve, 2009, A revision the Australian species of the ant genus Myrmecina (Hymenoptera: Formicidae), Zootaxa 2146, pp. 1-21 : 8-10

Myrmecina difficulta sp. n.

( Figs 6 , 12–16 , 49 )

Types. Holotype worker from Summit, Mt. Bellenden-Ker, 1700m, Queensland, 7 July 1971, R. W. Taylor & J. Feehan, moss forest (ANIC, ANIC32-047353); 8 paratype workers, same data as holotype (ANIC, BMNH, MCZC, ANIC32-047507).

Diagnosis. Dorsal surface of mesosoma with continuous longitudinal carinae running from pronotum to propodeum; carinae extending continuously from the posterodorsal surface onto the lateral surfaces of the anterior mesosoma (the carinae extend from the mesonotum to the sides of the pronotum), the sculpturing well developed on sides of pronotum. The form of the mesosomal sculpturing combined with the smooth region behind the compound eyes will separate this species from others known from Australia.

Worker description. Antennal scapes smooth or with low ridges. First segment of funiculus coneshaped. Sides of head behind compound eyes smooth. Sculpturing on dorsal surface of mesosoma varying from running longitudinally and generally with the central carina (or carinae) running nearly the length (the pronotum not differentiated from the mesonotum) to weakly “V”-shaped anteriorly. Carinae extending continuously from the dorsal surface onto the lateral surfaces of the mesosoma. Metanotal spines very short and broadly anglular. Propodeal spines long. Erect hairs abundant, straight. Colour dark brown-black, gaster slightly lighter, antennae, mandibles, legs and tip of gaster yellow.

Measurements. Worker (n = 24)— CI 93–107; HL 0.59–0.92; HW 0.54–0.91; MTL 0.28–0.49; SI 79–97; SL 0.45–0.82; WL 0.67–1.15.

Additional material examined ( ANIC except where noted). Queensland: 2.0km WNW Cape Tribulation (Site 2) (Monteith, Yeates & Thompson); 4km E Lake Barrine (Taylor,R.W. & Feehan,J.E.); 4.3km NE Mt. Perseverance (Burwell,C.) ( QMBA); 6.5km SSE Eungella (Gillison,A.); Alexandra Bay (Taylor,R.W. & Feehan,J.); Bellenden Ker Range, 1km S Cable Tower 6 (Earthwatch, Qld Museum); Bellenden Ker Range, Summit TV Stn (Earthwatch, Qld Museum; Monteith, Yeates & Thompson; Monteith,G.B. & Yeates,D.K.); Bellenden Ker Summit (Monteith,G.B.); Bellenden Ker, Centre Peak Summit (Monteith,G.B.); Brandy Ck. Rd., Conway S.F. (Monteith,G.B.); Crystal Cascades, via Redlynch (Monteith,G.B.); Hinchinbrook Is., Gayundah Ck. (Monteith, Davies, Thompson & Gallon); Kuranda, Black Mt. Road (Taylor,R.W. & Feehan,J.); Mt. Bartle Frere, below NW Peak Summit (Monteith,G.); Mt. Bartle Frere, Summit NW Peak (Monteith,G. & Monteith,S.); Mt. Dryander (Monteith,G.); Mt. Elliot (Taylor,R.W.); Mt. Fisher, 7km SW Millaa Millaa (Monteith, Yeates & Cook); Mt. Tyson, 2km W Tully (Yeates,D.K.); Mt. Windsor Tableland (Taylor,R.W.); Mulgrave River Road, 7km WbyS Bellenden Ker (Calder,A. & Weir,T.); Noah Creek (Taylor & Feehan); Noah Creek, 7km ENE Thornton Peak (Calder,A. & Weir,T.); Nob Creek, Byfield (Monteith,G.B.); Summit, Mt. Bellenden-Ker (Taylor,R.W. & Feehan,J.); Thornton Range (Taylor,R.W. & Feehan,J.); Tully Falls Nat. Pk (Taylor,R.W. & Feehan,J.E.).

Comments. This rainforest and palm forest species has been collected from leaf litter and under stones.

Myrmecina difficulta shows considerable morphological variation in a number of character systems, including the size, number and shape/configuration of carinae on the head and mesosoma, the development of sculpturing in the area behind the compound eye, the length of the metanotal spines and the overall body size. In some cases these characters show as much variation as that seen between other species in the genus, strongly suggesting that multiple closely related species are involved. For example the density of carinae on the mesonotum shows considerable variation, ranging from large and widely spaced to smaller and more dense. Similarly, body size is extreme in this species, showing more variation than that found in all other species combined – a highly unexpected and surprising condition.

However, this variation was found to be largely continuous and lacking obvious subdivisions. Additionally, there are numerous examples where significant variation is seen among specimens collected from the same litter sample, suggesting that this variation is intra- rather than inter-specific.

Additionally, the variation across characters showed little correlation. For example, many of the smaller specimens show a tendency to have the carinae on the dorsum of the pronotum in the form of a “V”, a pattern also seen in some of the largest workers but absent from the majority of intermediately sized specimens (where the carinae are more or less linear).

Combined, the lack of congruence among characters and the considerable variation found within individual characters make it difficult or impossible to subdivide the specimens treated here into diagnosable subsets. As a result these specimens are treated as belonging to a single heterogeneous species. It would be worth revisiting this conclusion as additional material becomes available.

Figures

FIGURES 5 – 6. Fig. 5, graph of head length versus head width for M. ampla, eruga, orbicula and pumila; Fig. 6, graph of head length versus head width for M. difficulta and the remaining Australian species.

FIGURES 12 – 16. Myrmecina difficulta sp. n. worker. Fig. 12, front of head; Fig. 13, lateral view of body; Fig. 14, dorsal view of body; Fig. 15, dorsal view of body; Fig. 16, dorsal view of body.

FIGURES 47 – 52. Distribution of material examined during this study. Fig. 47, M. alpina, M. pumila, M. silvalaeva, M. silvampla, M. silvangula, M. silvarugosa and M. silvatransversa; Fig. 48, M. australis; Fig. 49, M. difficulta; Fig. 50, M. eruga (circles) and M. rugosa (square); Fig. 51, M. inaequala; Fig. 52, M. wesselensis.