Description of Phasmarhabditis californica n. sp. and first report of P. papillosa (Nematoda: Rhabditidae) from invasive slugs in the USA

Abstract

A new species ofPhasmarhabditisand the known speciesP. papillosawere isolated from cadavers of invasive slugs in California.Phasmarhabditis papillosais the type of the genus and has not previously been reported from the Americas. Both species are characterised based on morphology, morphometrics and molecular data. Molecular phylogenies were inferred from concatenated DNA sequence alignments of nearly complete SSU and the D2-D3 domains of the LSU rDNA.Phasmarhabditis californican. sp. is characterised by a robust body, mature egg-laying specimens almost spindle-shaped when relaxed, 1.5 (1.3-1.8) mm long, tapering to a bluntly rounded anterior end with stoma about as long as lip region diam., six inner labial papillae and four outer cephalic papillae, pharynx with rounded to pyriform basal bulb, vulva located halfway along the body, hermaphroditic, didelphic, amphidelphic, and short, conoid tail constricted at one-third its length with prominent phasmids. Not a single male was found among five strains.Phasmarhabditis papillosais gonochoristic and has a longer isthmus, pyriform basal bulb and longer, dome-shaped spicate female tail constricted halfway along its length. Sequence analysis revealed unambiguous autapomorphies forP. papillosaandP. californican. sp. Phylogenetic analyses placed these two species in a monophyletic clade comprisingPhasmarhabditisspecies and other gastropod-parasitic taxa. Morphology, genetic distance, reproductive strategy and nucleotide autapomorphies support the new taxon.