Deepest starfish

The greatest depth at which a starfish has been documented is 9,990 m (27,560 ft) for a specimen of Hymenaster sp. of the Pterasteridae family, recorded in the Philippine Trench in the western North Pacific Ocean. It was reported by Mironov (1977) and was cited by marine invertebrate expert Dr Georgii Mikhailovich Belyaev in 1989.

Pterasterids sea stars are also known as deep-sea slime stars, so-called for the mucus they can produce as a means of self-defence.

The deepest observed sea star is also a Hymenaster sp. specimen at a depth of 7,176 m (23,543 ft) in the Java Trench in the eastern Indian Ocean, viewed in 2019 by scientists on board the deep-sea submersible Limiting Factor as reported in Frontiers in Marine Science on 8 March 2022.

Possibly the deepest-living echinoderm overall is a sea cucumber; a specimen of Prototrochus bruuni (formerly Myriotrochus bruuni) was logged at a depth of 10,730 m (35,203 ft) in the Tonga Trench in the south-west Pacific Ocean.