Clark, 1938
M. altimensis is a rusty-red sea cucumber (length < 25 mm) with white tentacles and tip of tail. The body is thin but rough. Spicules are tables with a moderate spire and numerous cross bars; there are similar forms with 4 recurved spines at the top ([l]m_altimensis_spicules_2.jpgM. altimensis spicules 2[/l]). M. altimensis has been dredged from soft black mud.