Colonies with soft, opaque, reddish test. Size over 20 m long and 1.2 m in diameter (Baker, 1971). Colony tapering from the narrow closed end to the broad open end, which is provided with a single, long whip-like process (Pyrostremma spinosum 1). Young colonies semi-globular, dome-shaped, with thick opaque test (Van Soest, 1974c). Ascidiozooids longer than high, with angular endostyle (Pyrostremma spinosum).
Collected in South Atlantic Ocean: Pyrostremma spinosum M