Gastrotrichs are a phylum of minute animals, generally less than a millimetre in length, found in interstitial spaces in sediments (a phylum is the highest classification of organisms below that of kingdom; other animal phyla include Molluscs and Arthropods, the Vertebrates only have the status of a subphylum within the Phylum Chordata, which also includes animals such as Sea Squirts and Lancets). Their small size meant that they went unnoticed until the event of microscopy, with the group not being discovered until the 1860s. These animals appear to be almost ubiquitous in marine and freshwater ecosystems, as well as semi-terrestrial ecosystems such as bogs and swamps, although the majority of non-marine species belong to one of the two orders of Gastrotrichs, the bottle-shaped Chaetonotida, with the other order, the worm-like Macrodasyida, far less common, and all coming from a single family, the Redudasyidae.
In a paper published in the journal Scientific Reports on 14 February 2019, André Garraffoni of the Department of Animal Biology at the State University of Campinas, Thiago Araújo of the Departament of Zoology at the Federal University of Minas Gerais, Anete Lourenço of the Department of Biological Science at the Federal University of Jequitinhonha and Mucuri Valleys, and Loretta Guidi and Maria Balsamo, of the Department of Biomolecular Sciences at the University of Urbino, describe a new species of Gastrotrich from Minas Gerais State, Brazil.
The new species is placed in the genus Redudasys and given the specific name brasiliensis, meaning 'from Brazil'. These Gastrotrichs are 302–376 μm in total body length, with a body separated into head, trunk and caudal (tail) regions. The head is rounded with several sensory cilia, but lacking tentacles or ocelli (simple eyes). The trunk is cylindrical, two-lobed at the posterior, and lacks a peduncle (narrow region to which the tail is connected). The body is covered by a smooth cuticle without ornamentation, and there are paired bristles along the sides. There are adhesive tubes at the front and rear of the animal.
Redudasys brasiliensis, Scanning electron micrograph in dorsolateral view and close-up of an anterior adhesive tube (inset). c, locomotory ventral ciliation; e, egg; m, mouth; ph, pharynx; sb, sensory bristles; TbA, anterior adhesive tubes; TbP, posterior adhesive tubes. Garraffoni et al. (2019).
Redudasys brasiliensis was found in sediments of the Jequitinhonha Drainage Basin, where it is relatively common, and sediments of the São Francisco Drainage Basin, where it was more rare. It's distribution beyond this is unknown. The locations where it was found were all above 900 m above sealevel, in rocky areas with a highly endemic (localised) vegetation.
Redudasys brasiliensis. Reconstruction of the musculature from confocal laser scanning microscopy images. (a) Schematic drawing of musculature in dorsal view. (b) Schematic detail of ventral musculature in the pharyngeal and the caudal regions. (c) Volocity-rendered 3D view of muscles in lateral view. Confocal micrographs of phalloidin-stained specimens. (d) Helicoidal muscles in the pharynx (arrow). (e) Detail of the pharynx posterior end with pharyngeal pores. asm, anterior semicircular muscle; cm, circular muscles; dlm, dorsal longitudinal muscles; llm, dorsal longitudinal muscles; mr, mouth ring, plm, pharyngeal longitudinal muscles; pp, pharyngeal pore; psm, posterior semicircular muscle; vlm, ventrolateral muscles. Garraffoni et al. (2019).
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