Stiliger sp.. A new species of sea slug?

I was in the Lembeh Strait in Indonesia recently, shooting macro video of tiny skeleton shrimps on a green algae stalk, when my dive guide Mamang and I noticed a small sea slug next to them.

This is a sacoglossan, a herbivorous animal commonly known as a sap-sucking slug. It pierces the algae and sucks out the sap from the cells.

Those large, clear appendages on the back are called the cerata, or kerata, and the green ducts are branches of its digestive gland. If you look closely you can see material traveling up and down those green ducts.

It's possible this is a solar-powered slug. Some sacoglossans keep chloroplasts from the algae alive in their body, where they continue to photosynthesize the sun's energy into sugars, a phenomenon known as kleptoplasty.

On the head you can see two black primitive eye spots, and a long pair of sensory stalks known as rhinophores. It looks like it's lost part of one of them. You can even see branches of the digestive gland in the head.

At first I expected this would be a known species of sea slug, but I've been unable to find any match, and I'm now told that it's probably a new species in the Stiliger genus. There are a few other species of Stiliger that have been observed in the field but not described and named.

It wouldn't be possible for scientists to officially designate this as a new species without examining samples. The form of the radular teeth for example is important in differentiating between species, and DNA testing is becoming increasingly important.

This specimen was at the dive site Jahir at a depth of 10 metres. It was just a few millimetres long. I'd love to hear from you if you believe this is a known species.

I shot this footage at while diving with YOS Dive Lembeh - Eco Beach Resort (http://yosdivelembeh.com/). Thanks to my dive guide and critter spotter Mamang.

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The video was shot by Nick Hope with a Panasonic GH4 in a Nauticam NA-GH4 housing. I used an Olympus M.Zuiko ED 60mm f2.8 macro lens and a Nauticam CMC.

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