Doing a search for the name unterhausen provided, I found a match on eBay that has all the peices laid out.

https://www.ebay.co.uk/itm/305117646890

Since it has the big nut, this might just be a cover on the outside that you just pry off. But, if it doesn't, then any prying might ruin it.

Still check underneath that black ring if it seems like it will stretch and pull out when you grab if with a pick or something.