Symplectic sigma models in superspace

21 pages, LatexWe discuss a special "symplectic'' class of N = 4 supersymmetric sigma models in (0+1) dimension with 5r bosonic and 4r complex fermionic degrees of freedom. These models can be described off shell by N = 2 superfields (so that only half of supersymmetries are manifest) and also by N = 4 superfields in the framework of the harmonic superspace approach. Using the latter, we derive the general form of the relevant bosonic target metric