mollusc? ID

I saw a few of these at Rowley Shoals last month and wold like to know what they are. It looks like a nudibranch but had no gills or distinct rhinophores.

Very light absorbant so challenging to get a clear picture.

Thanks,

Mark

Looks like Coriocella nigra to me.

Thanks, Coriocella sp looks right. The C. nigra images on the web are more amber coloured - is variable colour a feature of this species?

I often see them with this blue tinge.

-Mark