Eubostrichus fertilis sp. n., a new marine nematode (Desmodoridae: Stilbonematinae) with an extraordinary reproductive potential from Belize, Central America

Abstract

Eubostrichus fertilis sp. n. is described from fine subtidal sands in the Belize Barrier Reef system using LM and SEM illustrations and the sequence of the 18S rRNA gene. The new species is one of the smallest (mature specimens ranging from 1.88 to 3.03 mm) and the stoutest (a = 36-80) of all previously described Eubostrichus species. The closest relatives are E. parasitiferus and E. hopperi. It differs from the former in the more posterior position of the vulva and the postanal porids, and from the latter in the smaller size of the amphids, the shorter cephalic setae and the shape of the tail. Furthermore, it is remarkable for the prominent extent of the female genital system. Females have up to 18 eggs of similar size in their uteri. The body of the worm is covered by large (up to 45 μm long) crescent-shaped bacteria attached with both poles to the cuticle of the worm in a spiral pattern. The genus Eubostrichus is phylogenetically well supported on the basis of the 18S rRNA gene sequence. Eubostrichus gerlachi nom. nov. (= E. parasitiferus apud Gerlach, 1963 nec Chitwood, 1936) is proposed.

Phylogenetic confirmation of the genusRobbea(Nematoda: Desmodoridae, Stilbonematinae) with the description of three new species

“…Here large species of Stilbonematinae ( Laxus oneistus , Stilbonema majum ) and also R. hypermnestra are found in high densities (Ott & Novak, 1989 ). In contrast, a diverse assemblage of smaller Stilbonematinae species such as E. dianae , E. fertilis , R. agricola and R. ruetzleri inhabit the fine sands in the vicinity of lagunal mangrove islands and Thalassia testudinum seagrass beds (Ott et al , 2014 ). Additionally to the described species, several undescribed species and possibly genera of stilbonematine nematodes can be found in the shallow water habitats in the vicinity of Carrie Bow Cay (authors’ pers.…”

The importance of integrative approaches in nematode taxonomy: the validity of Parapharyngodon and Thelandros as distinct genera

“…Nematode identification has traditionally relied on morphological characters, but molecular approaches are crucial to detect cryptic and sibling species and to clarify taxonomic relationships (Nadler and Pérez-Ponce de León, 2011; Jorge et al ., 2014; Ott et al ., 2014). Despite this, the use of genetic tools in oxyurids is still not routinely implemented in most current taxonomic descriptions.…”

Morphology of obligate ectosymbionts revealsParalaxusgen. nov., a new circumtropical genus of marine stilbonematine nematodes

“…To date, a total of 10 different stilbonematine nematode genera and more than 50 different species are described (reviewed by Tchesunov 2013; Leduc 2013, Armenteros et al 2014b, Ott et al 2014a,b, Leduc and Sinniger 2018). Most species and genera still lack molecular data, but recent taxonomic work has started to integrate molecular data using the 18S rRNA gene (18S) (Ott et al 2014a, b; Armenteros et al 2014ab; Leduc and Zhao 2016, Leduc and Sinniger 2018) and the mitochondrial cytochrome oxidase subunit I (COI) gene (Armenteros et al 2014a, b). The phylogenetic signal of the two marker genes was however not consistent and called morphological genus and species identifications into question (Armenteros et al 2014b).…”

“…The phylogenetic signal of the two marker genes was however not consistent and called morphological genus and species identifications into question (Armenteros et al 2014b). While the monophyly of the subfamily Stilbonematinae has strong support based on 18S data (Kampfer et al 1998, Bayer et al 2009, van Megen et al 2009, Ott et al 2014a and b; Leduc & Zhao 2016), it was questioned in a recent study by Armenteros et al (2014b) which used both 18S and COI.…”

“…A trait that unites all stilbonematine nematodes is the conspicuous ectosymbiosis with sulphur-oxidizing Gammaproteobacteria that cover major parts of the cuticle (reviewed by Ott et al 2004). Stilbonematine symbionts have diverse morphologies, including rod, coccus, coccobacillus, filament, corn-kernel or crescent shapes, and each host species harbours a single morphotype (Ott & Novak 1989, Polz et al 1992; Polz et al 1994; Ott et al, 2004; Bayer et al 2009, Pende et al 2014, Ott et al 2014a, b). In phylogenetic analyses of the symbiont 16S rRNA gene (16S) sequences, all stilbonematine symbionts fall into a monophyletic clade of Gammaproteobacteria related to Chromatiaceae , which has been described as Candidatus Thiosymbion (from here on ‘Thiosymbion’) (Bayer et al 2009, Bulgheresi et al 2011, Heindl et al 2011, Zimmermann et al 2016).…”