A new Nectonema nematomorph species parasitic in an alpheid shrimp (Decapoda: Caridea)

We describe the marine horsehair worm Nectonema shimadaisp. nov., which was parasitic in a snapping shrimp (Alpheus sp.) collected at 4 m depth from the coastal water of Kikaijima Island, Japan, northwestern Pacific. The nematomorph was a female, 49 mm in length and 340 μm in width, salmon-pink when alive, with a translucent anterior body region and a distinct anterior chamber. The 18S sequence from N. shimadaisp. nov. was 12.8%, 9.8%, 9.6%, and 9.3% divergent in Kimura 2-parametar (K2P) distance from Nectonema sp. parasitic in the isopod Natatolana japonensis, Nectonema sp. parasitic in the crab Chionoecetes bairdi, N. munidae, and N. agile, respectively. In an 18S tree, N. shimadaisp. nov. was the sister taxon to a clade comprising three decapod-parasitic species, and species sharing the same host group or ocean were not monophyletic. The tree may reflect genetically distant warm- and cold-water lineages within decapod-parasitic nematomorphs.