Star-shaped spicules with conical rays are abundant in the test adding to firm consistence of the test and the mottled appearance.
Colour varies from dark and light grey to mustard yellow and purple.
Zooids (2-3 mm long) arranged in elaborated common cloacal systems.
Branchial siphon short and lobed, atrial opening with tongue like languet (may be bifid) on the rim of a large opening.
Retractor short and from the posterior end of the thorax.
The branchial sac has 4 rows of stigmata each with about 8-10 stigmata.
Gonads over the base of the gut loop, single ova and 3-5 male follicles under 4-6 coils of sperm duct.
Monniot, C.; Monniot, F.; Griffiths, C. and Schleyer, M. 2001 Ascidians of South Africa.108:1-141
Monniot, F. and Monniot, C. 1997 Ascidians collected in Tanzania.86:1-35
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