Two new Thermocyclops species (Copepoda, Cyclopoida) from Thailand, with notes on the genus phylogeny inferred from 18S and ITS sequences

With nearly 80 valid species, the genus Thermocyclops Kiefer, 1927 is one of the most speciose members of the family Cyclopidae. Although its centre of diversity is in the Sub-Saharan Africa, different species can be found in almost any non-glaciated part of the world. Six of them have been recorded so far from Thailand, all from lacustrine environments and with very wide distribution. It was therefore surprising to discover two endemic new species living sympatrically in a single cave. We describe their morphology in detail and assess affinities between them, and among them and the rest of their congeners. Judging by their morphology, one species has no close living relatives, while the other is very similar to the African T. hastatus Kiefer, 1952 and the Carribean T. antillensis Herbst, 1986. We use 18S and ITS nuclear markers to assess phylogenetic relationships of the new species, as well as to test the monophyly of Thermocyclops and a closely related genus Mesocyclops Sars, 1914. Both morphological data and reconstructed phylogenies reveal the two new species as only distantly related, which probably facilitates their sympatry. We were unable to challenge monophyly of either Mesocyclops or Thermocyclops, despite their diagnosis being essentially based on a single morphological character.