Berthellina delicata is common in the Marshalls, usually found under rocks on lagoon reefs and pinnacles at depths from the intertidal to at least 15 meters. We have seen specimens at both Kwajalein and Enewetak Atolls, and they have been observed at Rongelap by John and Lynette Flynn and at Ailinglaplap by Stan Jazwinski. They are active at night and eat a variety of sponges and hard corals. This was long known as Berthellina citrina, but Gosliner et al (2008) suggest that B. citrina is restricted to the Red Sea and that the one from the rest of the Indo-Pacific should be B. delicata (Pease, 1861). B. delicata is also common in Hawaii. Berthellina delicata was first reported in the Marshalls from Enewetak and Kwajalein Atolls as Berthellina citrina by Johnson & Boucher (1984) and Willan (1984).
Below is one of a number of individuals observed by Stan Jazwinski at Ailinglaplap in the shallow water on the reef flat.
There is a yellow Berthellina we used to think was a color form of this species. However, we noticed that when either form paired up or formed groups, they always did so with those that were colored the same. Apparently, as noted on the Sea Slugs of Hawaii page, there is now DNA evidence that the two color forms are in fact different species. This makes sense, since I'm sure that when pairing up, these animals are more capable of recognizing their own kind than we are.
The next two photos show individuals with different looking egg masses. The first is a pleurobranch egg mass but does not look like eggs we have seen from this species before, which are more like those in the second photo below.
Below shows one with a couple of egg masses, but the eggs may be someone else's.
The animal below had just been eating the red sponge. You can see a dug-out area in the sponge just back from under the anterior end on the left side of the photo.
Created 27 January 2007
Updated 4 August 2021