AN ENIGMATIC FRESHWATER CHAETONOTIDA (GASTROTRICHA) FROM BRAZIL: A NEW SPECIES IN A NEW GENUS

The phylum Gastrotricha includes over 800 free-living species of worm-like, actively moving microinvertebrates that represent an important component of the meiobenthic fauna of marine, brackish-water and fresh-water habitats. Global diversity of Gastrotricha from inland waters is less known than that of marine forms, and available information is extremely heterogeneous: in particular South America has been poorly studied. A new freshwater psammic species of Gastrotricha Chaetonotida was collected from sediments of high altitude streams in the Minas Gerais State, Brazil. A set of peculiar morphological features clearly distinguishes this taxon from all the other Chaetonotida: very large and closely juxtaposed cephalic plates wholly cover the head region both dorsally and ventrally; cuticular large, spineless, hexagonal scales partially overlapping and similar to each other coat the anterior and central trunk region both dorsally and ventrally; posterior trunk region coated by extremely large dorsal and ventral scales; two pairs of terminal ventral keeled scales, the external ones exceptionally large and double in size than the medial ones; long, thin caudal adhesive tubes composed of three sections. The taxonomic position of the new species within Chaetonotida and in particular into the family Chaetonotidae is discussed on morphological bases, and the reasons for its possible assignment to a new genus are advanced. Preliminary molecular data obtained from 18S rDNA analysis of the new taxon are presented within a phylogenetic tree of Chaetonotida, and its phylogenetic relationships are discussed.