title: An Integrated Morphological and Molecular Approach to the Description and Systematisation of a Novel Genus and Species of Macrodasyida (Gastrotricha).
abstract: BACKGROUND
  Gastrotricha systematics is in a state of flux mainly due to the conflicts between cladistic studies base on molecular markers and the classical systematisation based on morphological traits. In sandy samples from Thailand, we found numerous macrodasyidan gastrotrichs belonging to an undescribed species of difficult taxonomic affiliation. The abundance and original nature of the specimens prompted us to undertake a deep survey of both morphological and molecular traits aiming at a reliable systematisation of the new taxon.
  
  
  RESULTS
  Using several microscopical techniques we investigated the external and internal anatomy, including the muscular and nervous systems of the new species. Additional specimens were used to obtain the 18S rRNA gene sequence; molecular data was analysed cladistically in conjunction with data from additional species belonging to the near complete Macrodasyida taxonomic spectrum. Specimens are vermiform, up to 806 μm in total length, and show a well-defined head equipped with peculiar leaf-like sensorial organs and a single-lobed posterior end. The adhesive apparatus includes anterior, ventrolateral, dorsal and posterior tubes. Pharynx is about 1/4 of the total length and shows pores at its posterior 3/4. Adult specimens exhibit maturing eggs and a bulky, muscular caudal organ, but do not show sperm nor the frontal organ. Musculature and nervous system organisation resemble the usual macrodasyidan plan; however, the somatic circular muscles of the intestinal region surround all other muscular components and a third FMRFamide-IR commissure ventral to the pharyngo-intestinal junction appear to be an autoapomorphic traits of the new species.
  
  
  CONCLUSIONS
  While the anatomical characteristics of the Asian specimens appear so unique to grant the establishment of a new taxon, for which the name Thaidasys tongiorgii gen. et sp. nov. is proposed, the result of phylogenetic analyses based on the 18S rRNA gene unites the new genus with the family Macrodasyidae.
authors.affiliation: Department of Life Sciences, University of Modena and Reggio Emilia, Modena, Italy.
authors.forename: M Antonio
authors.initials: MA
authors.lastname: Todaro
authors.affiliation: Department of Life Sciences, University of Modena and Reggio Emilia, Modena, Italy; Consorzio Interuniversitario per il Centro di Biologia Marina ed Ecologia Applicata 'G. Bacci', Livorno, Italy.
authors.forename: Matteo
authors.initials: M
authors.lastname: Dal Zotto
authors.affiliation: National Museum of Natural History, Smithsonian Institution, Washington, D.C., United States of America.
authors.forename: Francesca
authors.initials: F
authors.lastname: Leasi
mesh_terms: D000818:Animals; D001499:Bayes Theorem; D044822:Biodiversity; D005618:Fresh Water; D007448:Invertebrates / Q000145:classification* / Q000502:physiology* / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D008857:Microscopy, Interference; D010802:Phylogeny; D012337:RNA, Ribosomal, 18S / Q000235:genetics / Q000378:metabolism; D013045:Species Specificity; D013785:Thailand
chemical_list: D012337:RNA, Ribosomal, 18S