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First record of Eulimids on brittle stars from Spratly islands of Vietnam

23/08/2021

The Eulimidae is a diverse group of symbiotic gastropods, most of which appear in tropical waters, but have not been fully studied. Worldwide, this family includes about 1,500 species, mostly known in symbiotic associations with all living classes of echinoderms. Eulimidae penetrate the skin of echinoderms, and their proboscis reach into the body cavity, vascular system or circulatory system, possibly feeding on mucus, phagocytic leukocytes or internal tissues of the echinoderm hosts. Some species feed on the dermis of echinoderms. Endosperm species of Eulimidae inhabit the gastrointestinal tract or large intestine cavity. In addition to their feeding activities, Eulimidae affects its host, causing lesions and bile formation, for example in brittle stars and sea lilies. In Vietnam, Eulimidae is still little researched. Previous studies have recorded 15 species, but only 3 species have been detected with their hosts.

Two specimens of brittle star Ophiothrix (Acanthophiothrix) purpurea with Eulimidae snails were collected from the surface of two soft coral colonies at 20-25 m depth on a drop off near the Central London Reef (Truong Sa Dong), during the scientific expedition of Vietnam - Russia Tropical Center in June 2019.

Fig. 2 The brittle star Ophiothrix (Acanthophiothrix) purpurea on different corals: a - Stereonephtya sp., b - Sinularia sp. (photo by Y.V. Deart)

Research results show that, for the first time, two species of snails Stilapex zebra and Pyramidelloides sp. (Eulimidae family) on the arm of the brittle stars. In previous studies, only snails of the Eulimidae family were found on the Ophiuroidea brittle class in Central Vietnam (Nha Trang Bay), while this study first recorded a symbiotic relationship between Eulimidae species and Ophiuroidea from another area of the East Sea - the Spratly Islands. For the brittle stars, this was also the first time recorded as a host for both Stilapex zebra and Pyramidelloides sp. This may suggest that the brittle star Ophiothrix (Acanthophiothrix) purpurea is a common symbiotic with many high-level hosts (mainly soft corals). If so, this could be considered a very interesting example of a supersymbiosis between mobile invertebrates: the brittle star is a symbiotic of soft corals, and the Eulimidae snail is the symbiosis organism of the brittle star.

Eulimids on the brittle star arm: a – two specimens ofStilapex zebra and three Pyramidelloides sp., b – three specimens of Pyramidelloides sp. (photo by Y.V. Deart)

Eulimids on the brittle star arm: a - two specimens of Stilapex zebra and three Pyramidelloides sp., b - three specimens of Pyramidelloides sp. (photo by Y.V. Deart)

Shells of eulimids from Ophiothrix (Acanthophiothrix) purpurea: a - Stilapex zebra, female, b - Pyramidelloides sp. (photo by E.S. Mekhova)

Source: Dgebuadze P.Y., Deart Y.V., Do Huu Quyet, 2020. First record of eulimids on brittle stars from Spratly Islands. Symbiosis, 81(2): 201-205. DOI:10.1007/s13199-020-00694-9

 Nguyễn Quốc Khánh/Institute of Tropical Ecology