Gastrotrichs of the genus Chaetonotus Ehrenberg, 1830 (Chaetonotida, Chaetonotidae) are known to be a speciose and pervasive group in both the marine and freshwater ecosystems, and recent investigations indicate that there is a significant amount of species diversity yet to be discovered. In the present study, a new species of this genus is described from two quarry lakes in northern Italy and characterized using an integrative morphological and molecular approach. Chaetonotus polites n. sp. is recognized by a rather stocky body, a five-lobed head, and the cuticular covering resolved in 13 alternating columns of partially imbricated scales, trilobed on the head and pentagonal on the trunk; each scale bears a peculiar simple, very thick, curved spine with a truncated apex. The new species is also distinguished by four putative molecular apomorphies at the 18S rRNA gene and two at the 28S rRNA gene. The location and type of these unique traits in the predicted secondary structure of the ribosomal genes is provided. The phylogenetic analysis based on concatenated sequences of three genes (the nuclear 18S and 28S rRNA genes and the mitochondrial COI gene) derived from 123 selected chaetonotidans, including the novel species, confirms that the genus Chaetonotus is a polyphyletic group, with several of its members resolved together with species of other genera. The new species forms a cluster with species of the subgenus Hystricochaetonotus Schwank 1990, suggestive of its potential stem lineage |
