Can anyone help with this?

[ceepee83]

This is some weird slug/nudibrach that moves like a caterpillar. Anyone know what it is and if it’s good or bad?

Thanks in advance

 

[ISpeakForTheSeas]

You're going to need some higher contrast pics of the slug - any chance you could get it in a container of tank water and take some pics of it from the top and the side (showing the full body length with both) under white light, preferably against a black background?

 

[ceepee83]

Thanks for your reply but I’ve lost the bugger now. I’ll try and repost if I can.

 

[ceepee83]

Do the new images help?

 

[ISpeakForTheSeas]

Do the new images help?

A bit, yes. Probably a sacoglossan (sap-sucking) slug, possibly an Elysia species, though I can't tell for sure from the pics - if it's a sacoglossan slug, then it's an algae-eater (an herbivore).

Do you have any macroalgae in your tank?

 

[ceepee83]

Yes I do but I don’t know what type they are. It has sprung up on live rock purchased from a tank closure. I’ll do some research. Thank you very much.