Notably, nkx3 [28], foxj [30], the hox gene paralog anthox1 [28] and irx [28] are also expressed in the apical region devoid of six3 in Nematostella; foxj matches the region devoid of six3 expression in sea urchin [38] and apical irx expression has been documented in hemichordates, although broader than in annelids
[25].