The taxonomy of the family Xyalidae Chitwood, 1951 (Monhysterida: Nematoda): a cladistic analysis

Abstract

A cladistic analysis of the family Xyalidae has been carried out, with selected Monhysteridae and Sphaerolaimidae as presumptive outgroups. Forty nine characters, taken from published descriptions, were scored for 91 species from 33 genera. The way in which the characters were coded is illustrated by drawings and graphs. Phylogenetic analyses were conducted with the programs PAUP*4.0d65 and PAUP*4.0b2. Neighbour-joining and parsimony trees were constructed and the preferred consensus parsimony tree is presented. The tree has been divided into 15 groups for purposes of discussion. All eight species of Monhysteridae form a separate clade consistent with outgroup status, but the four species of Sphaerolaimidae are not separated from Xyalidae. Several of the Daptonema species, Pseudosteineria plus Steineria, and Rhynchonematinae form three well supported clades. Other groupings are much less well supported and are presumed to be paraphyletic. Many published descriptions do not include suf cient detail to allow relationships to be determined and suggestions are made as to data which should be included in future taxonomic descriptions of Xyalidae.

The state of the art of Xyalidae (Nematoda, Monhysterida) with reference to the Brazilian records

“…This genus was originally described with the name Macramphis by Timm (1961) in the family Sphaerolaimidae and renamed later for Megalamphis to avoid homonymy with another already existing genus of terrestrial nematode described previously by Altherr (1950). Since then the genus is considered as a taxon of Sphaerolaimidae by some authors (Timm 1961;Andrássy 1976) and of Xyalidae by others (Lorenzen 1978;Nicholas and Trueman 2002). In the present work we agree with the original description by Timm (1961) and the last revision of Xyalidae (Fonseca and Bezerra 2013) that considered it as a genus of Sphaerolaimidae.…”

“…Species belonging to Daptonema, Theristus, Trichotheristus and Zygonemella were the only ones encountered in estuarine sediments (Table 1). Interestingly is that these four genera are not necessarily monophyletic (Nicholas and Trueman 2002;Fonseca and Bezerra 2013), suggesting that the colonization of inland waters Habitats of occurrence were classified as sandy beaches (SB) or estuary (EST). PR Paraná, SP São Paulo, RJ Rio de Janeiro, ES Espirito Santo; PE Pernambuco; PA Pará.…”

“…Nicholas and Trueman (2002) recognized 33 genera in their cladistic analysis whereas Fonseca and Bezerra (2013) accepted 44 genera and also mentioned the number of valid species of each genus. The total number of valid species also varies enormously within Xyalidae.…”

Guitartia tridentata n. gen., n. sp. (Monhysterida: Xyalidae) and Macrodontium gaspari n. gen., n. sp. (Chromadorida: Microlaimidae), free-living marine nematodes from the Caribbean Sea

“…The family Xyalidae Chitwood, 1951 appears to be monophyletic after Meldal et al (2007) and within-family relationships have been revised, according to cladistic principles based on morphological and morphometric features, by Nicholas and Trueman (2002). According to these authors, the family is characterised by an annulated cuticle, six outer labial setae plus four cephalic setae arranged in one circle, and female with a single, outstretched, anterior ovary.…”

“…From our results, an emended diagnosis of the family is proposed. In their analysis, Nicholas and Trueman (2002) recognised 33 genera within the family. Other genera have been included in the meantime: Arabanema Turpeenniemi, Nasira & Maqbool, 2001;Cienfuegia;Dactylaimoides Blome, 2002;Enchonema Bussau, 1993;Manganonema Bussau, 1993;Marisalbinema Tchesunov, 1990;Paragonionchus Blome, 2002;Paramphimonhystrella Huang & Zhang, 2006;Parelzalia Tchesunov, 1990;Pseudechinotheristus Blome, 2002;and Sacrimarinema Shoshin, 2001.…”