I just stumbled upon a wiki article:
In the section "simultaneity" theres a description of a model which says that both variables are codetermined ,i.e. each affecting the other, and it's a static SEM
The model is
$y_i = \beta_1 x_i + \gamma_1 z_i + u_i$
$z_i = \beta_2 x_i + \gamma_2 y_i + v_i$
My question is: What does static in this context mean? My guess is that though it's a dynamic model we actually can't observe the dependency between $y_i$ and $z_i$. One would need at least one additional "shifter" in order to observe these dependencies.