Orkney Liberal Democrat MSP Liam McArthur said his “blood ran cold” when he learned that a member of the Ewing dynasty had been promoted to the Scottish Government.
He described Annabelle Ewing, the newly appointed minister for youth and women’s employment, as having a “partisan and utterly unconstructive approach” to politics.
Mr MacArthur, Liberal Democrat education spokesman, made the remarks at a fringe meeting at the Lib Dem conference in Dumfermline on Saturday, the day after First Minister Nicola Sturgeon unveiled her new cabinet.
Ms Ewing, a Mid Scotland and Fife MSP, is the daughter of SNP legend Winnie Ewing and sister of Inverness and Nairn MSP Fergus Ewing.
A spokesman for the SNP hit back at Mr McArthur and said his “personal attacks are unbecoming and ill-judged”.
“He complains about an unconstructive approach to politics whilst indulging in these unpleasant remarks,” the spokesman added.
“Is it any wonder the Lib Dem poll ratings have fallen through the floor and they are now struggling to out-poll the Monster Raving Loony Party?”
Reflecting on the cabinet reshuffle which resulted in Mr Russell being replaced with Angela Constance, Mr McArthur said: “On a personal level I surprisingly got along with Mike Russell quite well.
“But he had an ego the size of a planet, is hugely arrogant and definitely somebody who thought the minister knows best.
“But this departure will lead to a change in style and hopefully a change in substance with Angela Constance who has done a pretty good job in her previous role.”
Mr McArthur said he thought Ms Constance would approach education issues in a different way to her predecessor.
“But as they say the Lord giveth and the Lord taketh away and the prospect of Annabelle Ewing in this portfolio turns my blood cold,” he added.
“Whatever Mike Russell is Annabelle Ewing is something altogether worse in terms of her partisan and utterly unconstructive approach to anything.
“Ministerial office may mellow her slightly but I will not hold my breath.”