  The presence of HI gas in galaxies is inextricably linked to their morphology
and evolution. This paper aims to understand the HI content of the already
identified 2210 dwarfs located in the low-to-moderate density environments of
the MATLAS deep imaging survey. We combine the HI observations from the
ATLAS$^{3D}$ survey, with the extragalactic HI sources from the ALFALFA survey,
to extract the HI line width, velocity and mass of the MATLAS dwarfs. From the
1773 dwarfs in our sample with available HI observations, 8% (145) have an HI
line detection. The majority of the dwarfs show irregular morphology, while 29%
(42) are ellipticals, the largest sample of HI-bearing dwarf ellipticals (dEs)
to date. Of the HI dwarf sample, 2% (3) are ultra-diffuse galaxies (UDGs), 12%
have a transition-type morphology, 5% are tidal dwarf candidates, and 10%
appear to be disrupted objects. In our optically selected sample, 9.5% of the
dEs, 7% of the UDGs and 10% of the classical dwarfs are HI-bearing. The
HI-bearing dwarfs have on average bluer colors than the dwarfs without detected
HI. We find relations between the stellar and HI masses, gas fraction, color
and absolute magnitude consistent with previous studies of dwarfs probing
similar masses and environments. For 79% of the dwarfs identified as satellites
of massive early-type galaxies, we find that the HI mass increases with the
projected distance to the host. Using the HI line width, we estimate dynamical
masses and find that 5% (7) of the dwarfs are dark matter deficient.

Astrophysics of Galaxies