Perhaps ticks answer close to right one (5)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

A charade of A (‘answer’) plus CA ( circa , ‘close to’) plus R (‘right’) plus I (‘one’). Acari was an old taxonomic subclass including mites and ticks, but recent genetic studies have shown that they fall into two orders not as closely related as had been thought, so the term acari has been dropped..