u/Exciting-Network-455

I have just moved house, and it appears that I did not do my due diligence during the inspection, as I have only just noticed this black substance while going about cleaning the bathroom. Is it mould or something else? My gut instinct says it’s black mould, but I don’t have any experience with black mould so I am probably just jumping to conclusions. Is it worth messaging the landlord over this? Thank you in advance.