* Dermatobranchus semilunus Gosliner & Fahey, 2011 Figure 19E

Material examined.

One specimen 33 mm, TB.

Ecology.

Exclusive to the soft sediment habitats outside the coral reef. Observed on Dendronephthya sp. octocoral, though active feeding was not observed. Depth 14-24 m.

Distribution.

Known from the West Pacific including Malaysia, the Philippines, Indonesia, and Papua New Guinea (Gosliner and Fahey 2011). Here documented as a first record for Thai waters.

Remarks.

Specimens from Koh Tao are sometimes found with a pale yellow-pink margin to the oral veil. A similar trait is known from the closely related Dermatobranchus fasciatus Gosliner and Fahey 2011; however, the present specimens externally match D. semilunus based on other characteristics. Additionally, similar pigment appears to be visible in a photograph of a specimen in the original description of the species (Gosliner and Fahey 2011: fig. 74C).