The black Protogen missile ship that carried the protomolecule, captured the Scopuli crew, lost control of its infection, and was later destroyed by the Rocinante.
The Anubis is the black, radar-defeating stealth vessel found tethered beside Julie Mao's asteroid marker. It carries capital-ship-buster torpedoes, advanced stealth systems, and the physical evidence of a mission that captured the Scopuli crew. Its security record shows those prisoners confined, abused, and overwhelmed when the infection aboard the ship breaks loose. The crew and captives are reshaped into an impossible mass around the reactor; Julie Mao alone escapes after accessing the records and venting the vessel.
Dresden identifies the vessel by name at captured Thoth Station. He confirms that losing the Anubis was a major blow to Protogen's schedule and that Julie's infected body on Eros allowed the company to recover the 'viral agent' anyway. This makes the ship the direct bridge between the Phoebe protomolecule, Julie's flight, the Canterbury trap, and Eros's experimental outbreak. James Holden's crew has already scuttled it to prevent contamination and recovery, but its surviving data has exposed the project it served.
The Anubis is a long, lean, black stealth missile ship with radar-deflecting curved hull geometry, almost invisible against space, and a large internal bay of twelve capital-ship torpedo tubes.
The Anubis is the lost Protogen delivery vessel whose failure placed the protomolecule on Eros and left the chain of evidence the Rocinante follows.