What Is this? Safe or not?

[smotard]

Dear reef friends, I am a beginner in marine aquariology, I am writing from Italy. DSB tank of 1 year and 10 months with soft corals, anemones and some LPS which is perhaps beginning to proceed with dignity in recent months. After finding and removing some small orange flatworms on the base of a bastomussa I occasionally check the tank with a flashlight with the lights off. Last night I found on a rock, near xenia, the flatworm (or nudibranch?) visible in the attached photos. Length about 3cm. Do you know what it can be? Is it harmful to the reef? Can I leave it? Thanks in advance for the advice!

 

[IKD]

Nudi of some sort. Generally these either starve out as hitchhikers, are not coral safe (lettuce and berghia are exceptions). Others may have more precise ID of this one.

 

[Dburr1014]

Dear reef friends, I am a beginner in marine aquariology, I am writing from Italy. DSB tank of 1 year and 10 months with soft corals, anemones and some LPS which is perhaps beginning to proceed with dignity in recent months. After finding and removing some small orange flatworms on the base of a bastomussa I occasionally check the tank with a flashlight with the lights off. Last night I found on a rock, near xenia, the flatworm (or nudibranch?) visible in the attached photos. Length about 3cm. Do you know what it can be? Is it harmful to the reef? Can I leave it? Thanks in advance for the advice!

They are hard to ID most of the time.
Unless you know of the origin, better to take out.

 

[ISpeakForTheSeas]

Welcome to Reef2Reef!

That's an Elysia sp. sacoglossan slug, likely E. obtusa or E. flava - Elysia spp. are sometimes called lettuce nudibranchs, though they're not actually nudibranchs at all. They're harmless algae eaters.

 

[smotard]

Thank you! I am amazed at the speed and accuracy of the response! I looked at photos on google and it looks just like Elysia Fava or Elysia Obtusa. I haven't added new corals for over a month and I only saw it tonight. It is currently in a plastic cup with aquarium water. If tonight it's still alive I'll put it back on the rock to graze on seaweed I think.
Thanks everyone, I figured I could find answers in this awesome forum!