Morphological and molecular study on Yininemertespratensis (Nemertea, Pilidiophora, Heteronemertea) from the Han River Estuary, South Korea, and its phylogenetic position within the family Lineidae.

Taeseo Park,Shi-Chun Sun,Hiroshi Kajihara,Sang-Hwa Lee

doi:10.3897/zookeys.852.32602

Abstract

Outbreaks of ribbon worms observed in 2013, 2015, and 2017–2019 in the Han River Estuary, South Korea, have caused damage to local glass-eel fisheries. The Han River ribbon worms have been identified as Yininemertespratensis (Sun & Lu, 1998) based on not only morphological characteristics compared with the holotype and paratype specimens, but also DNA sequence comparison with topotypes freshly collected near the Yangtze River mouth, China. Using sequences of six gene markers (18S rRNA, 28S rRNA, histone H3, histone H4, 16S rRNA, and COI), the phylogenetic position of Y.pratensis was inferred among other heteronemerteans based on their sequences obtained from public databases. This analysis firmly placed Y.pratensis as a close relative to Apatronemertesalbimaculosa Wilfert & Gibson, 1974, which has been reported from aquarium tanks containing tropical freshwater plants in various parts of the world as well as a wild environment in Panama.

Highlights

An explosive proliferation of unidentified, brackish-water heteronemerteans was observed in the Han River Estuary, South Korea, in the spring of 2013
We report the identity of Han River nemerteans based on morphological characteristics in comparison to the type material of Y. pratensis as well as DNA barcoding data from the type locality
The external feature of the Han River nemerteans agreed with the original description of Y. pratensis in that these worms were variously dark brown, brick red, and tinged with violet sometimes (Fig. 2A, B)

Summary

Introduction

An explosive proliferation of unidentified, brackish-water heteronemerteans was observed in the Han River Estuary, South Korea, in the spring of 2013. In the 2015 bloom, more than 90% of catches were worms, with none to only a few eels that were dead (Lee 2015) probably due to yet-unidentified neurotoxic substances (Kwon et al 2017) in worm mucus within the concentrated net catches These neurotoxins might have been discharged from epidermal cells and contained in the secreted mucus (cf Tanu et al 2004; Asakawa et al 2013). To our knowledge, this is the first record of damage to fisheries directly caused by nemertean outbreaks, a potentially indirect case is known. The milky ribbon worm Cerebratulus lacteus (Leidy, 1851) has been identified as an important threat to populations of the softshell clam Mya arenaria Linnaeus, 1758, which is one of the commercial bivalves in Atlantic Canada, no outbreak has ever been reported for C. lacteus (cf. Bourque et al 2001, 2002)

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Conclusion