Livingston keeper Liam Kelly, Aberdeen defender Michael Devlin and Kilmarnock trio Stuart Findlay, Greg Taylor and forward Eamonn Brophy are all ancillary.
Clarke worked with striker Brophy and defenders Find-lay and Taylor during his spell at Rugby Park.
"All the boys deserve to be there," said Clarke.
"People will look at it and probably think, 'he's just picking players from Kilimanjaro for the sake of it'. It's not true.
"Stephen O'Donnell is an established player at right-back, seven caps. Stuart Findlay was in the last squad that Alex picked, Stuart has had a great season. Iit was a case of promoting Greg up from the very good performances he has had for Scotland Under-21s. Up front I have a lot of injury problems and Eamonn Brophy was an obvious choice for me."