Can I book a seat on the Glacier Express from Zermatt to Disentis?

Question

I want to take the Glacier Express from Zermatt and disembark at Disentis.

However, on http://www.glacierexpress.ch/, when I select Zermatt as my starting point, my destinations are limited to the following:

Note that this leg isn't mentioned on the Glacier Express ticket price list either.

Am I able to book this leg? If so, how?

Edit #1: Further to my original question, is there any difficulty disembarking at Disentis after buying a longer ticket to Chur? Note that I'll have a few suitcases with me.

Edit #2: Per Andrew Lazarus' post, this particular segment of the Glacier Express route can be booked on sbb.ch (option 1 in the screenshot in Andrew's response). The first class fare is CHF 153, as opposed to CHF 204 for Zermatt -> Chur.

Answer 1

Even though this is on a private railway, you may buy the ticket at the SBB-CFF-FSS site. (That’s three acronyms in German, French, and Italian for the one Swiss State Railways.) Choice of language is in tiny letters near the top of the screen.

I have just checked, and I could have booked Zermatt-Disentis by either the Express or a combination of local trains.

The following screenshot shows the availability of the GEX ticket from Zermatt, disembarking at Disentis:

Answer 2

The 'Glacier Express' is a special kind of train, more of a tourist attraction than a transport service and the sales manual suggests that only certain segments can be booked.

One option would be to book a longer segment that you actually want. Alternatively, if you are happy to travel on just a train rather than the 'Glacier Express', you could take the ordinary trains which run on the same route, which run hourly. The tradeoff is that it would take 5 hours instead of 4 and you would have to change trains twice. I think it should also be cheaper. You can see these connections by searching here and using the advanced search to restrict the result to 'R' trains only.