Doris pecten  Collingwood, 1881

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Doris pecten is placed in most publications on sea slugs in the genus Doriopsis. It is characterised by the arrangement of the gills in a transverse line across the back, and a dorsal flap covering the gill opening. The mantle is blue-green, to dark blue, and covered with numerous small pustules, some higher in the axis of the back, which is usually paler and has criss-cross pattern caused by the underlying spicules. It feeds on a deep blue sponge of the genus Terpios.
IPN places this species in the genus Doris
Gosliner, Terrence M., David W. Behrens & Ángel Valdés. 2008. Indo-Pacific Nudibranchs and Sea Slugs. Sea Challengers Natural History Books.
Gig Harbor, Washington. 426pp. at page 157
Let me quote from the Identification of Doris granulosa: "Species with a pectinate gill where often placed in a separate genus, Doriopsis, but are now considered to be a subgroup within Doris."
More information on Doris pecten as Doriopsis pecten are on Bill Rudman's Sea-Slug Forum!