Mo. Rev. Stat. § 509.060

The plaintiff in his petition or in a reply setting forth a counterclaim and the defendant in an answer setting forth a counterclaim may join either as independent or as alternate claims as many claims either legal or equitable or both as he may have against an opposing party. There may be a like joinder of claims where there are multiple parties if the requirements of sections 507.030, 507.040 and 507.060 are satisfied. There may be a like joinder of cross-claims or third-party claims if the requirements of section 509.460 and section 507.080, respectively, are satisfied.