Costasiella usagi Ichikawa, 1993 Figure 4B

Material examined.

Three specimens 2-6 mm, LB.

Ecology.

In soft sediment habitats beyond the coral reef where it feeds predominantly on Avrainvillea longicaulis and less commonly on Vaucheria sp. An individual of the species has been observed to be naturally captured and ingested by the free-living coral Heteropsammia cochlea with subsequent investigations suggesting the species may represent viable prey for the coral in soft sediment habitats (Mehrotra et al. 2019). Depth 10-18 m.

Distribution.

Across the Indo-Pacific including India (Dixit et al. 2017), Singapore (Jensen 2009), Japan (Ichikawa 1993), Malaysia, the Philippines, Papua New Guinea, Australia, and Guam (Gosliner et al. 2008). Known from the Gulf waters of Thailand (Mehrotra and Scott 2016).