Rhabditis (Oscheius) Guentheri1 Sp.N., an Unusual Species With Reduced Posterior Ovary, With Observations On the Dolichura and Insectivora Groups (Nematoda: Rhabditidae)

Abstract

The hermaphroditic species Rhabditis guentheri sp. n. from decaying tissue of rice plants in Vietnam is described, separated from previously described Rhabditis species by its more or less reduced posterior ovotestis. In rare cases sperms or oocytes are formed in it, though it could not be determined whether eggs ever matured and were fertilized. Only three degenerate males were found. This species exhibits a very poor fecundity with a maximal number of 60 offspring. The new species belongs to the Dolichura-group. Though the species of the Insectivora-group have a leptoderan and those of the Dolichura-group a peloderan bursa, there are convincing apomorphic characters to hypothesize both as sister taxa. They are united under the subgenus name Oscheius (Andrássy, 1976) with Dolichorhabditis as junior synonym. So a peloderan bursa must have been evolved independently within Rhabditis; and Pellioditis is not monophyletic. Diagnoses are presented for Oscheius, the Dolichura-group (seven species) and the Insectivora-group (five species); likewise a key to identify all the known species of the Dolichura-group. Rhabditis brzeskii is nom. nov. for Cruznema velatum Brzeski, 1989. R. guentheri sp. n. is a transitory form to a nematode possessing only an anterior hermaphroditic gonad. This form is discussed in detail in the more general context of whether a didelphic or a monodelphic condition is primitive within nematodes and if there are constraints for a reduction of one genital branch.

Operons and SL2 trans-splicing exist in nematodes outside the genus Caenorhabditis

“…The isolate CEW1 is an undescribed sibling species of Rhabditis (Oscheius) tipulae, a member of the Dolichura Group (35). Placement of CEW1 and R. tipulae in a genus is actively under investigation (L. Carta, personal communication), but CEW1 is provisionally called Dolichorhabditis.…”

Evaluation of Some Vulval Appendages in Nematode Taxonomy

“…Although the structure is asymmetric and seals the vulval opening, it would not be large or superficial enough to be considered a flap. Epiptygmata and vulval membranes may be present in the same nematode, as in Coslenchus costatus; Antarctenchus hooperi Siddiqi, 1980(Siddiqi, 1980; or Rhabditis (Oscheius) guentheri (Sudhaus and Hooper, 1994). However, epiptygmata do not seem to coexist with vulval flaps, at least nominally in published descriptions.…”

“…9). Small vulval membranes also were observed with the SEM in Rhabditis (Oscheius) guentheri Sudhaus and Hooper, 1994, described as ''longitudinal cuticular flaps 8-10 mm long … at each end of the vulval slit,'' (Sudhaus and Hooper, 1994). An SEM view of a related free-living rhabditid nematode, Pellioditis pellio (Schneider, 1866) Timm, 1960, showed no vulval appendages (Eveland et al, 1990).…”

“…7); Cooperia verrucosa Mönnig, 1932;andCooperia okapi Leiper, 1935 (Hoberg et al, 1993c); and in bacterial-feeding facultative or phoretic parasites Rhabditis (Choriorhabditis) dubia Bovien, 1937(Osche, 1952 (Sudhaus and Kühne, 1989) and Rhabditis (Caenorhabditis) sonorae (Sudhaus and Kiontke, 1996). In Rhabditis (Oscheius) guentheri (Sudhaus and Hooper, 1994) and Caenorhabditis elegans, they are only easily seen with the SEM. However, in the monotypic genus Operculorhabditis Khera, 1969 membranes are described as deciduous, an exceptional condition for cuticular membranes in the literature.…”

The occurrence of three species of the genus Oscheius Andrássy, 1976 (Nematoda: Rhabditida) in Iran

“…The genus is in the family Rhabditidae Ör-ley, 1880 (Andrássy 2005). According to Sudhaus (1976) and Sudhaus and Hooper (1994), species of the genus form two separate subclades. The 42 known species of the genus are clustered in two Insectivora and Dolichura groups (Tabassum et al 2016).…”