What is the equivalent of theme_menu_item in Drupal 7? I know that in drupal 6 exist: theme_menu_item, but in drupal 7 there is not. Is there any replacements so that I modify the output for main system menu ?

Actually I want to do a kind of filter of the menu items depending some criteria, which I will set in the function.
Looking at the function that called the theme function theme_menu_item() (menu_tree_output()), and comparing it with the Drupal 7 version of the same function, I can say that the equivalent of theme_menu_item() is theme_menu_link().