Moriarty had been suffering from what the Lions said was nerve damage and was restricted to just one appearance on the tour during the 13-7 victory over the Provincial Barbarians in the opening match.
Gatland had earlier called lock Cory Hill, hooker Kristian Dacey, scrumhalf Gareth Davies and prop Tomas Francis, who were in New Zealand on duty with Wales.
He later added prop Alan Dell and flyhalf Finn Russell to the squad after Scotland beat Australia 24-19 in Sydney.
The Welsh quartet had joined the Lions in Rotorua, where the visitors clinically ground down the Maori All Blacks 32-10.
With the additions, Gatland will now be able to run two separate teams, with the new players likely to feature in the 'midweek' squad against the Waikato Chiefs on Tuesday and Wellington Hurricanes the following week.
"We have said all along that we need to give ourselves the best chance of winning the test series and that could potentially involve calling up players," he said in an earlier statement.
"Bringing in these players from an identical time zone, who can hit the ground running and step straight in rather than having to adjust following long-haul travel, will help us manage players before the first test, give us quality training numbers to prepare properly as well as offering us options for selection for the Chiefs match."
(Reporting by Greg Stutchbury; Editing by Peter Rutherford/Amlan Chakraborty)
