Arter helped the Cherries rise from League One to the Premier League, and has played 69 matches in the top flight over the last three seasons.
Under the terms of the loan agreement, Arter will be ineligible for selection when Cardiff visit Bournemouth in their league opener on Saturday.
Camarasa passed a medical at Cardiff's training ground on Thursday and could be in line for a debut against Bournemouth.
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The 24-year-old Spaniard, who came through Valencia's academy, helped Betis finish sixth in La Liga last season.
The midfield duo took Cardiff's total of new recruits to six since they gained promotion back to the top flight having spent a season there in 2013-14. All their other signings, including Norwich City winger Josh Murphy, have come from England's second-tier.
(Reporting by Martyn Herman; Editing by Ken Ferris and Ed Osmond)
