  We numerically study a simple model for thermo-reversible colloidal gelation
in which particles can form reversible bonds with a predefined maximum number
of neighbors. We focus on three and four maximally coordinated particles, since
in these two cases the low valency makes it possible to probe, in equilibrium,
slow dynamics down to very low temperatures $T$. By studying a large region of
$T$ and packing fraction $\phi$ we are able to estimate both the location of
the liquid-gas phase separation spinodal and the locus of dynamic arrest, where
the system is trapped in a disordered non-ergodic state. We find that there are
two distinct arrest lines for the system: a {\it glass} line at high packing
fraction, and a {\it gel} line at low $\phi$ and $T$. The former is rather
vertical ($\phi$-controlled), while the latter is rather horizontal
($T$-controlled) in the $(\phi-T)$ plane. Dynamics on approaching the glass
line along isotherms exhibit a power-law dependence on $\phi$, while dynamics
along isochores follow an activated (Arrhenius) dependence. The gel has clearly
distinct properties from those of both a repulsive and an attractive glass. A
gel to glass crossover occurs in a fairly narrow range in $\phi$ along low $T$
isotherms, seen most strikingly in the behavior of the non-ergodicity factor.
Interestingly, we detect the presence of anomalous dynamics, such as
subdiffusive behavior for the mean squared displacement and logarithmic decay
for the density correlation functions in the region where the gel dynamics
interferes with the glass dynamics.
