The Association of Ophiothrix lineata and Callyspongia vaginalis: A Brittlestar‐Sponge Cleaning Symbiosis?

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Abstract
The relationship between a sponge,Callyspongia vaginalis,and an associated brittlestar,Ophiothrix lineata,was examined for mutualistic symbiotic interaction. Cinematography, feeding experiments, and analyses of stomach contents reveal thatO. lineata(unlike otherOphiothrixspecies) is a non‐selective deposit feeder. Its diet consists of detrital particles adhering to the sponge, which are too large to be utilized by the sponge as food. Thus, the brittlestar cleans the inhalent surface of the sponge as it feeds. Since siltation interferes with sponge pumping‐activity, it is suggested that the cleaning behavior ofO. lineatamay enhance the filtration capability ofC. vaginalis. In situelapsed‐time films show that brittlestars expose their arms when they feed, suggesting that they feed only at night because of a need to avoid diurnal predators. Manipulative experiments show that residence inC. vaginalisprotectsO. lineatafrom predatory fish. A comparison of the incidence of arm regeneration for brittlestars residing onC. vaginalis,and on a toxic sponge,Neofibularia nolitangere,indicates that factors other than sponge toxicity are involved in protecting sponge‐dwelling brittlestars.