Specialized predation by deep-sea Solenogastres revealed by sequencing of gut contents.

'Who eats whom?' is a fundamental question about the ecological roles and interactions of deep-sea organisms. However, the tools needed to analyze trophic relationships remain limited, especially with regard to studying meiofauna and small macrofauna in abyssal and hadal depths. We present results from indirect molecular analyses of the gut contents of abyssal and hadal Solenogastres (Mollusca, Aplacophora) of the Northwest Pacific. Our data revealed a high food specialization and a surprising diversity of food sources among these inconspicuous worm-shaped predators. We hypothesize that Hydrozoa forms the ancestral food source of Solenogastres, and that specialization on non-cnidarian prey (such as annelids, nemerteans, and bivalves) evolved independently along with modifications in the digestive tract. Despite being intuitively advantageous in the nutrient-limited deep sea, we found only one widespread generalist feeder (potentially associated with scavenging).