One of the two living species of Coelocanth. These are famously refered to as "prehistoric" or "living fossils"; both terms are erroneous, but that's a topic for an esoteric rant, some day.
The white marks are not disease or specimen decay, they're pigment patches that researchers have used to identify individuals, in much the same way that other marine animals such as Orcas and Grey Whales are tracked. There are lots and lots of pictures of these guys on the web, so I'll put up another one.
Fishbase refers to videos of interesting Latimeria behaviour, but I couldn't find any good videos on GoogleVideo or YouTube.