First report of marine horsehair worms (Nematomorpha: Nectonema) parasitic in isopod crustaceans

Abstract

Nectonema, the only horsehair worm (Nematomorpha) genus found in marine environments, was previously known to be parasitic only in decapod crustaceans. We report Nectonema sp.as the first record of a marine nematomorph parasitic in isopod crustaceans. This is also the third record of marine nematomorphs from the North Pacific. Six infected isopods (Natatolana japonensis) collected from 1425 m depth in the Sea of Japan each contained one to seven (mean 2.33) nematomorphs in the body cavity in the pereon. There was no correlation between the host body length and number of parasites. For Nectonema sp., we describe and illustrate morphological features of the parasitic juvenile stage and present nucleotide sequences for the cytochrome c oxidase subunit I gene (COI or cox1; 451 nt), 18S rRNA gene (1777 nt), and region spanning the internal transcribed spacer 1 (ITS1) and the 28S rRNA gene including the 5.8S rRNA gene and ITS2 (1218 nt in total). In an 18S maximum-likelihood tree that included 24 nematomorph species, Nectonema sp. grouped with N. agile from the northwestern Atlantic; the 18S gene from these two taxa was divergent by 11.8% K2P distance, suggesting they are different species. Nectonema species may have a broader range of host groups than previously suspected, but may have been previously misidentified as nematode parasites.

Flatworm cocoons in the abyss: same plan under pressure

“…For the COI gene, newly designed primers COI_MarF (CAAATTGGACATCCTGARGTTTATA) and COI_ MarR (AATTAATAACGRCGAGGCAT) were used for PCR amplification and cycle sequencing. For the 18S gene, primers SR1 and SR12 [11] were used for amplification, and primers SR3, 18S-b3F, 18S-b4F, 18S-b4R, 18S-b5F, 18S-b6F, 18S-a6R and 18S-b8F [11][12][13][14][15] for cycle sequencing. For the 28S gene, primers 28S_1F and 28S_6R [16] were used for amplification, and primers 300F, 300R, 900F, 28S_Rd4.2b [17,18] and 28S_b5F (TATCCGGTAAAGCG AATGATTAGA, newly designed in this study) for cycle sequencing.…”

Digenean Metacercariae Parasitic in a Staurozoan Cnidarian

“…It can be challenging to ascertain the intermediate host for a particular parasitic species, and this information is lacking for many parasites. This is especially the case for parasites utilizing unexpected taxa, where novel hosts are generally discovered only fortuitously (e.g., Escobar-Briones et al, 1999;Kakui, 2014;Kakui et al, 2021).…”

First detection of Colletotrichum fructicola (Ascomycota) on horsehair worms (Nematomorpha)

“…However, some species have only freshwater hosts and a free-living freshwater adult stage (Schmidt-Rhaesa 2012). In addition to the freshwater ones, there are marine horsehair worms (all belonging to the genus Nectonema) that parasitise crustaceans as juveniles and live in surface seawater as adults (Schmidt-Rhaesa 2012, Kakui et al 2021). Moreover, two recently-described Nematomorpha live in terrestrial wet environments in the adult phase (Anaya et al 2019, Chiu et al 2020).…”