|A re-evaluation of the Macrothrix rosea-triserialis group, with the description of two new species (Crustacea Anomopoda: Macrothricidae)|
|Dumont, H.J.; Silva-Briano, M.; Babu, K.K.S. (2002). A re-evaluation of the Macrothrix rosea-triserialis group, with the description of two new species (Crustacea Anomopoda: Macrothricidae). Hydrobiologia 467(1-3): 1-44. dx.doi.org/10.1023/A:1014933227259|
|In: Hydrobiologia. Springer: Berlin. ISSN 0018-8158, more|
Animal morphology; Distribution; New species; Taxonomy; Cladocera [WoRMS]; Macrothricidae Norman & Brady, 1867 [WoRMS]; ; ; ;
Cladocera; Macrothricidae; taxonomy; males; trunk limbs; species groups and subgroups; world distribution
We redescribe Macrothrix rosea (females and males) based on material collected in Belgium. We also compare seven populations of Macrothrix `triserialis' from different parts of the world, including a topotypical population of M. triserialis s. str. from Sri Lanka, and males from South India (here first described), relying heavily on the structure of the trunk limbs, beside classical features of morphology. M. rosea and M. triserialis are extremely closely related: males are easily separated, but the identification of females requires micro-characters such as the relative length of the apical segment of the setae natatoriae and the adornment of the first antenna and of the longest swimming seta of the antenna. M. rosea and triserialis together constitute a sub-group of the rosea-group.
Macrothrix triserialis-like animals occur in the tropical–subtropical belts of four continents. We compare populations from Asia, South America and Africa, and find differences in microcharacters of the trunk limbs, but cannot decide whether these represent random variation or sound taxonomical differences.
One of the basic characters of the Macrothrix rosea-triserialis subgroup is that the setae natatoriae of the postabdomen are implanted on a prominence, the `heel'. Other characters include the fact that the Fryer' forks are adorned with one or two big teeth only, and that the scrapers of trunk limb two form a row of eight without any doublings. Possibly, scraper five, and scraper four to a lesser degree has an enlarged subapical tooth. The exopodite of trunk limb three has four plumose setae, the back and front row of the endopodite six setae and/or receptors, the exopodite of trunk limb four has two setae, and the back row of the endopodite six setae, plus one on the gnathobase. The pre-epipodite of trunk limb five consists of three lobes, the `endopodite' is small, and the `exopodite' is reduced to a single seta. The male postabdomen has a tubular ending, without true end-claws, although a rudiment of an end-claw is seen in M. triserialis.
Two new species are described: M. tabrizensis and M. agsensis. A comparison, including the males of Macrothrix triserialis, M. rosea, M. smirnovi and M. tabrizensis confirms the relationship of all these taxa, but also reveals a morphological series in the shape of the postabdomen, from a complete absence of end-claws, over rudiments of a pair of end-claws, to complete endclaws. Absence of end-claws is here considered to represent an evolved character state. Macrothrix smirnovi Ciros & Elías (1987) is less closely related to the rosea-triserialis group, and is considered to form a sub-group in its own right. It shows a short `heel' on the postabdomen, but carries a supplementary seta behind scraper 4 of the endopodite of trunk limb two, and has a male with a postabdomen that closely resembles that of the female. These are primitive characters, which are also found in Wlassicsia, Bunops and Onchobunops and provide a possible phylogenetic link between Macrothrix and these three genera, although the genetic distance between them is considered to be quite large.