A Novel Parasitic, Syndinean Dinoflagellate Euduboscquella triangula Infecting the Tintinnid Helicostomella longa

Jung Min Choi,Ki Hong Kim,Young Ok Kim,D. Wayne Coats,Jae Ho Jung

doi:10.3389/fmars.2021.720424

Abstract

A tintinnid species, Helicostomella longa, infected by the parasitic dinoflagellate Euduboscquella triangula n. sp. was discovered from the southern coast of Korea in August of 2015 and 2016. Parasite morphology and development were analyzed by observation of live cells and protargol-stained specimens. The parasite was determined to be a new species in the genus Euduboscquella based on morphological and molecular data. A representative sequence of the novel species clustered in Euduboscquella group I. The morphological and developmental features of E. triangula were distinguished from those of its congeners by: (1) numerous shallow and intertwining grooves on an inconspicuous shield; (2) sporocytes initially forming a short chain, but separating after the second or third division regardless of spore type; (3) production of motile mushroom-shaped dinospores, non-motile spherical spores, and non-motile triangular spores. Dinospores were formed by ca. 28% of infections, while both non-motile spherical and triangular spores occurred at a frequency of ca. 36%. All spore types showed completely identical 18S rDNA sequences. Parasite prevalence was 15.5 and 8.3% on 17 and 24 August of 2015, respectively, with infection intensity on both dates being 1.3.

Highlights

The genus Euduboscquella (Coats et al, 2012) was erected for syndinian dinoflagellates previously included in the genus Duboscquella (Chatton, 1920)
Of the morphological and morphogenetic attributes exhibited by Euduboscquella species, sporogenetic pattern, spore morphology, and shield (= episome) structure have proven most useful in distinguishing taxa
Coats and Bachvaroff (2013) distinguished three patterns of sporogenesis among species of Euduboscquella infecting tintinnids: (1) production of a tightly packed cluster of sporocytes that separate following the final division to produce dinokont spores (= dinospores) or non-dinokont spores (= spores with one or no flagella); (2) production of a very long string of sporocytes that mature into dinokont spores; and (3) production of a short string of sporocytes that separate, continue to divide, and produce non-dinokont spores

Summary

Introduction

The genus Euduboscquella (Coats et al, 2012) was erected for syndinian dinoflagellates previously included in the genus Duboscquella (Chatton, 1920). The nine current species of Euduboscquella are intracellular parasites of protists, with six described from tintinnid hosts, one from aloricate ciliates, and two from dinoflagellates. A single tintinnid species can be parasitized by more than one species of Euduboscquella (Coats and Bachvaroff, 2013). Diversity of sequences within the Euduboscquella subclade of MALV Group I includes numerous cryptic species. Comparison of host and parasite rDNA phylogenies based on single cell isolates indicates that multiple tintinnid species are parasitized by undescribed Euduboscquella morphospecies (Bachvaroff et al, 2012)

Methods

Results

Conclusion