Parry, 20, will get the chance to prove his credentials at Rodney Parade in the Dragons' Amlin Challenge Cup clash with Rugby Mogliano on Sunday.
Gustafson, still learning his trade in his first full season as a hooker following a switch from loosehead prop, is among the replacements.
Former flanker Appleyard insists both have the talent required to fill in for 35-year-old Jones - and believes they have a golden chance to get their foot in the door.
"It's a great opportunity for them and we need them to step up for us," Appleyard told the South Wales Argus.
"Doors open in funny ways - I got a chance at Swansea because Richard Webster went to rugby league.
"Every player has a story about how they got their opportunity and Sam and Hugh has been told 'if you want it, go out and claim it'.
"While we are gutted about losing Steve, something positive can come out of his injury if the other boys respond to the challenge and fill his jersey.
"It isn't just at hooker where that opportunity is there - throughout the team there are chances to make a claim for places in the side against the Blues and Ospreys over Christmas."
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