Identification Key to the Intracontinental Species of the Genus Diaptonema (Nematoda: Monhysterida: Xyalidae) with a Description of New Species D. borkini sp. nov

Abstract

Until recently, the system of the family Xyalidae was extremely complicated. The characters of the genera Theristus, Cylindrotheristus, Mesotheristus, Pseudotheristus, Mongolotheristus, and others were mixed up. Many species changed their generic assignment more than once. The most recent revision (Venekey et al. 2014) resulted in the fact that in intracontinental water bodies two species only preserved their independence: Daptonema and Sacrimarinema. Genera Cylindrotheristus, Mesotheristus, Mongolotheristus, Penzancia were partially reduced to synonyms of Daptonema. The basic character in taxonomy of genera is terminal setae. This cannot be used in some cases as some individuals in some populations lack terminal setae. Development of the system of the family Xyalidae and genus Daptonema, in particular, is possible under consideration of such characteristic as spicule form and presence of tail papillae. The hermaphrodite specimen of D. borkini sp. n. is discussed separately. The article provides an identification key to intracontinental species of the genus Daptonema. The key shows the species to be found in intracontinental water bodies. The species recorded in rivers (as a rule, in estuaries and lower parts of rivers) are not taken into account, as they seem to be the marine species which are capable to survive in significantly desalinated water. The article provides the description of new species D. borkini sp. n., which is similar in morphology to D. salinae Gagarin et Gusacov, 2014 and D. limnobia Wu et Liang, 2000. The key is supplemented with the Table of the main characteristics of all intracontinental species (males) of the genus Daptonema.