Common species along intertidal rocky shores and on the upper regions of submerged shallow reef pinnacles were they form dense aggregations.
Individuals can grow to a large size (up to 20cm in diameter).
Two large siphons open in the upper part of the body close together.
This species lack the pointed papillae on and around the siphons as is characteristic of Pyura herdmani.
The test may be clean and relatively smooth to heavily encrusted by various other organism such as algae, sponges or other ascidian.
Elaborately branched tentacles form a ring at the opening of the branchial sac.
Dorsal tubercle in the form of two spiral cones.
Branchial sac has 6 folds with longitudinal vessels.
The oesophagus is long, the stomach voluminous with a large hepatic gland and the intestines form a loop obscured by endocarps.
Single gonads on each side are divided into lobes which may be hidden by endocarps.
Millar, R. H. 1962 Further descriptions of South African ascidians56:113-221
Monniot, C.; Monniot, F.; Griffiths, C. and Schleyer, M. 2001 Ascidians of South Africa.108:1-141
Shenkar, N.; Gittenberger, A.; Ruis, M.; Rocha, R. M.; Swalla, B.; et al. 2017 Ascidiacea World Database. Atriolum marinense Kott, 2001. Accessed through: World Register of Marine Species at: http://www.marinespecies.org/aphia.php?p=taxdetails&id=250052 on 2019-03-12