Riethia, Kieffer, 1917

Cranston, Peter S., 2019, Riethia (Kieffer 1917) (Diptera: Chironomidae) revised for the Austro-Pacific region, Zootaxa 4646 (3), pp. 461-500 : 495

Riethia larva ‘A’

Material examined, larval head capsules only: AUSTRALIA, 4L, New South Wales, Currowan S.F., Cabbage Tree Ck., 35°34'S 150°02'E, 2.i.2009 ( MV AU09CTCR1, 2, 4, 5); L, same, except 23.i.2000 (Cranston & Dimitriadis); L, Glenbog SF., Brown Mountain , Fastigata Rd, Rutherford Ck., 36°36’S 149°47’E, 909 m a.s.l, 4.ii.2009 ( MV NSWRGCR4 ) .

Molecular data shows that four larvae from Cabbage Tree Ck ( CTC) (collected 2.i.2009) are essentially identical and belong to a clade distinct from any others with molecular sampling. These larvae are smaller than any congener measured from Australia ( Table 2 ). Although it is possible they might be 3 rd instars, this seems unlikely given that in all other species in which 3 rd and 4 th instars are known, the size ratio of 4 th to 3 rd instar for sclerotised structures (head, postmentum and mandible lengths) is 1.6 (that is 4 th is 160% length of 3rd), and is nearer to 2 for the basal antennal segment. The small larva ‘A’ is only a negligible outlier to the smallest other 4 th instars described ( Table 2 ). The larvae show some unexpected variability in morphology: the antennal flagellum can extend to the base of the 4 th antennal segment or significantly beyond the terminal, and the clypeus approximates that of R. queenslandensis ( Fig. 6M ) in shape and size, especially with regard to the curved posterior boundary but with weaker antero-lateral flare. Given that these 4th instars can be keyed, significant features from the antenna can be recognised as being the low AR of 0.9–1.1, 3 rd segment shorter than the 2 nd and with an evenly and completely sclerotised wall to the 3 rd segment. Morphology of this larval molecular cluster suggests 2 additional unreared larvae (lacking molecular data) belong to the clade. The occurrence of this larval type in both Cabbage Tree and Rutherford Creeks, but seemingly nowhere else, cannot allow association by sympatry as both sites support several coexisting species.

Figures

FIGURE 6. Riethia spp. Larva. Mid-dorsal head:A. R. donedwardi, sp.n., B. R. noongar sp.n.. Clypeus: C. R. larval sp. ‘C’, D. R. azeylandica sp.n., E. R. cinctipes Freeman, F. R. donedwardi sp.n., G. R. hamodivisa sp.n., H. R. neocaledonica sp.n., I. R. noongar sp.n., J. R. paluma sp.n., K. R. phengari sp.n., L. R. plumosa Freeman, M. R. queenslandensis sp.n., N. R. stictoptera Kieffer, O. R. wazeylandica sp.n., P. R. zeylandica Freeman.