Layered dihaloids of iron group elements (NiCl2, CoCl2, CoBr2 etc.) are easy plane antiferromagnets. Spontaneous reduction of in-plane symmetry in these crystals takes place under magnetic ordering due to magneto-elastic interaction. As a result, spatial degeneration for the antiferromagnetic vector L direction in the easy plane leaves. In the spectrum of low frequency antiferromagnetic resonance a distinctive gap appears. However, study of magnetostriction of these antiferromagnets has shown the absence of the averaged spontaneous deforming crystal's plane in the absence of external magnetic field H-perpendicular to applied in the base plane. This is related with formation of multidomain structure in antiferromagnetic (A-F) crystal. Spontaneous strains of the easy plane in each of the domains are present. But they are differently directed and mutually indemnified for the sample as whole. Earlier AF domains in given crystals were discovered by neutron diffraction method. The in-plane magnetic field converts crystal in the one-domain state with LH (perpendicular to). A deformation of the plane of crystal as whole appears herewith. A multidomain structure is restored practically reversible at the removal of the field. It is grounded that given domain structure is connected with elastic long distance forces under spontaneous magnetostrictive deformation of easy plane antiferromagnets. Such domains must be considering as magneto-elastic ones.