Mariaglaja inornata is seen in a variety of mostly lagoon reef and pinnacle habitats. Often if you see one, there will be others in the near vicinity. We also have this species from the Solomon Islands. Mariaglaja inornata was first reported in the Marshalls from Enewetak and Kwajalein Atolls as Chelidonura inornata by Johnson & Boucher (1984).
When they are out, you can often catch two or more in the act of mating, as in the two photos below.
This specimen released the reddish substance when disturbed.
Unless they are eating it, most opisthobranchs seem to avoid crawling on coral. Yet we often see Mariaglaja inornata on live colonies of various hard corals, particularly Montipora. They appear to eat tiny flatworms found on the coral.
In October 2011, there was a sudden bloom in the population on a pinnacle reef near Kwajalein we dive frequently. We have seen a few individuals here before, but on October 10 and 11, we saw many: about 36 on the 10th and well over 50 (where I stopped counting) on the 11th. Nearly all were on live Montipora coral, and appeared to be using their mouths as little vacuum cleaners. I still have not seen what they are trying to eat. Many were mating, and one cluster (second photo below) depositing egg masses on a chunk of mostly dead Acropora coral resting on a Montipora colony.
Created 27 January 2007
Updated 7 November 2021