Tambja morosa, also known as Tambja kushimotoensis or gloomy nudibranch,[3] is a species of sea slug, a dorid nudibranch, a shell-less marine gastropod mollusk in the subfamily Nembrothinae[4] within the family Polyceridae.

It is found in the Philippines, Indonesia, Thailand, Myanmar, Malaysia, New Zealand, Solomon Islands, Taiwan, Australia, French Polynesia, Fiji and Hawaii.

This large species of Tambja grows to approximately 70–75 mm in length.

This species is normally black with blue markings, although dark green specimens are found in the cooler waters of New South Wales and northern New Zealand.

[7] Tambja morosa feeds on arborescent bryozoan colonies.