Agnatha

Agnatha was a Federation ambassador, and an aquatic life-form native to the planet Jezero.

In 2269, Agnatha boarded the USS Enterprise (NCC-1701) on a diplomatic mission to Detente Station 1 for peace talks with the Romulan Star Empire. Unfortunately, Agnatha was murdered enroute to the conference by Dr. Geoffrey M'Benga, who was under the control of alien spores.

(TOS novel: Death's Angel).