Halanonchus scintillatulus sp. nov. from New Zealand and a review of the suborder Trefusiina (Nematoda: Enoplida)

Abstract

We provide a review of the enoplid suborder Trefusiina Siddiqi, 1983, based on morphological considerations and analyses of new and published 18S rDNA sequences. We also describe Halanonchus scintillatulus Leduc sp. nov. from the Hauraki Gulf, northern New Zealand, as well as females of Trefusialaimus idrisi Leduc, 2013 from the continental slope of New Zealand. We show for the first time that the structure of the female reproductive system of Trefusialaimus Riemann, 1974 consists of two opposed and outstretched ovaries, an unusual feature for the Enoplida. The Trefusiina did not form a monophyletic group in the 18S rDNA phylogeny due to the placement of Lauratonema Gerlach, 1953 and Trefusialaimus sequences well away from the main Trefusiina clade. However, due to generally weak Maximum Likelihood support values, we refrain from changing the classification of these taxa until more comprehensive analyses can be conducted. Our phylogenetic analysis supports the inclusion of the Trischistomatidae Andrássy, 2007 within the Trefusiina, meaning that all of the enoplid suborders now include at least some terrestrial/freshwater representatives. The Trefusiina currently comprises five families, 14 genera and 92 valid species.

Twenty Years after De Ley and Blaxter—How Far Did We Progress in Understanding the Phylogeny of the Phylum Nematoda?

“…Phylogenetic relationships within Enoplida ( Figure 2 a), as inferred based on 18S rRNA, are poorly resolved in nearly all studies [ 13 , 16 , 17 , 18 , 21 , 24 , 25 ] except for [ 26 ] who used Bayesian Inference and a very limited dataset. The cladogram depicted on the Figure 2 a is in part based on our own analysis presented in the Supplementary Materials Figure S1 .…”

“…The first includes the families Rhabdolaimidae and Campydoridae (E8 in Figure 2 a) that always form a well-supported monophyletic clade, also confirmed by morphology-based studies [ 28 ]. The second consists of Trefusiidae and Trischistomatidae and Tripyloididae (E9 in Figure 2 a) that are also usually grouped in a well-supported monophyletic clade [ 9 , 17 , 24 ], although the data quality may affect the support for the monophyly of the family Trefusiidae [ 25 ]. Within this clade, monophyletic Trefusiidae is nested within paraphyletic Trischistomatidae [ 19 , 20 ] ( Figure S1 ), and the placement of Trischistomatidae in Enoplida, instead of Triplonchida (previously placed in the family Tripylidae [ 2 , 3 ]) is supported by the morphological evidence [ 29 ].…”