These are brittle stars, photographed in the 1920s for the Records of the South Australia Museum. These specific ones are from “Dr. Verco’s collection in St. Vincent and Spencer Gulfs,” and are apparently very different from other Ophiactis species. It’s from an article by American researcher Hubert Lyman Clark, cataloguing “The Sea-Lilies, Sea-Stars, Brittle Stars, and Sea Urchins of the South Australia Museum,” which I found in the Biodiversity Heritage Library.
Ophiactis tricolor is a graceful member of graceful family, but I can’t find much else about it online. I guess they’re not large or charismatic enough to be the stars of their own marine portraits. Just small stars in the sea.