Hi Francois,
There seem to be 3 species here.
The first I'd suggest Holothuria dakarensis (or poss. H. tubulosa - Panning described dakarensis as a subspecies of tubulosa)  

From: flmnh-aspidolist [mailto:[log in to unmask]] On Behalf Of François Michonneau
Sent: 05 March 2014 15:51
To: [log in to unmask]
Subject: Fwd: Trans. : holothurians of the Dakar area

Hello all,

  I received these cuke pictures taken from Dakar, Sénégal by a French naturalist who is getting worried about Chinese prospectors who want to harvest them. I'm not familiar with the fauna, but maybe some of you are. Do you have any IDs?

  -- François