This looks like Trapania sp. 6 in Gosliner et al (2018). Specimens have been found by Peter and Marissa Brown and Jay Lord both on red sponge on pier pilings and on the large sponge Ianthella basta in Kwajalein lagoon. The nudibranchs measured about 6mm stretched out.
Thie photo below was from red sponge covered with the entoprocts that make up the diet of this Trapania.
The specimen below on a field of entoprocts on orange sponge was found and photographed on the lagoon side of Kwajalein Island by Christina Sylvester.
Another pair from Kwajalein Island by Christina Sylvester, feeding on entoprocts similar to those in the previous photo. Christina reported seeing numerous specimens during the summer of 2017 on a variety of entoproct laden sponges and ranging in length from about 5 to 12mm.
Created 3 February 2016
Updated 9 October 2021