Michalakus Plisko, 1996

Plisko, Jadwiga Danuta, 2013, A new family Tritogeniidae for the genera Tritogenia and Michalakus, earlier accredited to the composite Microchaetidae (Annelida: Oligochaeta), African Invertebrates 54 (1), pp. 69-69 : 82

The genus Michalakus Plisko, 1996

contains only one species, M. initus Plisko, 1996 ( Fig. 11 ).

Species incertae sedis: T. benhami (Michaelsen, 1900) and T. crassa Michaelsen, 1918 .

Distribution: Tritogeniidae species are known from a limited area of the north-eastern part of the RSA. Tritogenia species have been found at the northern border of the Eastern Cape province, extending through KZN, Mpumalanga and Limpopo, to the Limpopo River as the northern boundary of their diestribution range. However, their occurrence may be expected in neighbouring Botswana, Zimbabwe, Swaziland, and Mozambique. They are distributed from the sea level up to higher altitudes in the Drakensberg escarpments and eastern Soutpansberg range. Although mostly recorded from unpolluted grassland, indigenous bush, and river bank biotopes, some of the species ( zuluensis and douglasi ) are to be found in fairly disturbed, contaminated places.

The monotypic genus Michalakus has been recorded in a more restricted area in the KZN midlands in the vicinity of the Umgeni River valley, where species of Tritogenia have also been encountered. Although initus , the sole species of Michalakus , has been collected in only a few localities, it could also occur in neighbouring sites.

Discussion: In respect of the majority of the species, evidence of speciation, species endemism and marked restriction to certain ecological conditions are of particular note.At present, with knowledge of the evolutionary history of Oligochaeta still being limited, the idea that the Tritogeniidae have undergone separate evolutionary development during various geological periods is a speculative concept. The characters noted in Tritogenia and Michalakus differ notably from these observed in species of the Microchaetidae (s.str.). The meroic excretory system, which has been viewed primarily as a generic character for Tritogenia , may be considered as homoplasy, being frequently seen in other Oligochaeta. However, its occurrence together with the complex of instantly recognizable characters ( Table 2 ), supports its unambiguous value. Extended study of these characters may shed more light on the evolutionary situation as regards the indigenous South African megadriles. Recent data based on selected gene sequences observed in T. lunata (James & Davidson 2012) indicate a basal sister-group relationship with the microchaetid species. A follow-up molecular study on the indigenous South African megadriles may elucidate the evolutionary position of the Tritogeniidae .

Figures

Fig. 11. Michalakus initus Plisko, 1996, holotype.