The self-archived version of this journal article is available at Linköping University Institutional Repository (DiVA): http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-139605 N.B.: When citing this work, cite the original publication. Lagerkvist, V., Wahlström, M., (2017) ed variables, and say that a co-clone closed under such denitions is polynomially closed, and otherwise superpolynomially closed. We investigate properties of polynomially closed co-clones and prove that if the corresponding clone contains a k-ary near-unanimity operation for k ≥ 3 then the co-clone is polynomially closed, and if the clone does not contain a k-edge operation for any k ≥ 2, then the co-clone is superpolynomially closed. For the Boolean domain we strengthen these results and prove a complete dichotomy theorem separating polynomially closed co-clones from superpolynomially closed co-clones. Using these results, we then proceed to investigate properties of strong partial clones corresponding to superpolynomially closed co-clones. We prove that if Γ is a nite set of relations over an arbitrary nite domain such that the clone corresponding to Γ is essentially unary, then the strong partial clone corresponding to Γ is of innite order and cannot be generated by a nite set of partial functions.