November 6, 1999
From: Valda Fraser
Thanks for the information on Ceratosoma tenue. Here is an unidentified black arminid.
Locality: South Coast of Kwa Zulu Natal, South Africa, near Port Shepstone, on coarse sand between low profile scattered rocky reef, Depth: 36m, June 1999.
firstname.lastname@example.orgFraser, V., 1999 (Nov 6) Armina from South Africa. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/1481
A number of species of Armina were described earlier this century from South Africa. Unfortunately most were described from from preserved specimens and not surprisingly their colour in preservative had become 'blackish with white lines'.
I think they will only be sorted out when their anatomy is studied. from a quick look at the descriptions, your animal seems to differ from them all in having relatively few longitudinal mantle ridges (usually about 30). I am pretty sure it is a species of Armina, but again, a closer look at the anatomy would be needed to confirm that.