The first record of symbiosis between a new species of scaleworm (Polychaeta, Polynoidae) with fungiid corals (Scleractinia, Fungiidae)

Among scleractinian coral-associated symbionts, polychaetes contribute relatively less to overall species richness compared to crustaceans and mollusks, with only 40 documented symbiotic species. Notably, scaleworm (Polynoidae) diversity on scleractinian corals remains remarkably low, with just nine species recorded to date. During biodiversity surveys in the Tho Chu Archipelago (southern Vietnam), we discovered polynoid polychaetes inhabiting fungiid corals Pleuractis moluccensis and Fungia fungites. Specimens were collected, preserved in ethanol, and examined through morphological and molecular analyses, leading to the formal description of Hololepidella martini sp. nov. This new species is distinguished from congeners by: (1) its exclusive association with fungiid corals, (2) the presence of only bidentate neurochaetae, and (3) a uniformly white or yellowish body lacking distinctive pigmentation. Molecular analyses of COI gene fragments further support the distinction between H. martini and its closest relative, H. nigropunctata, revealing 14–15% genetic divergence. Field surveys showed significantly higher prevalence on P. moluccensis (33%, n = 78) than on F. fungites (6%, n = 65), suggesting the former serves as the primary host, while the latter is a secondary alternative. This discovery represents only the fourth known species of coral-associated polynoids, highlighting both the rarity of such symbioses and the need for further research on coral-polychaete relationships.

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