  We analyse the properties of three unusual dwarf galaxies in the Centaurus A
group discovered with the HIPASS survey. From their optical morphology they
appear to be low surface brightness dwarf spheroidals, yet they are gas-rich
(M_{HI}/L_{B} > 1) with gas-mass-to-stellar light ratios larger than typical
dwarf irregular galaxies. Therefore these systems appear different from any
dwarfs of the Local Group. They should be favoured hosts for starburst, whereas
we find a faint star formation region in only one object. We have obtained
21-cm data and Hubble Space Telescope photometry in V and I bands, and have
constructed Colour Magnitude Diagrams (CMDs) to investigate their stellar
populations and to set a constraint on their age. From the comparison of the
observed and model CMDs we infer that all three galaxies are at least older
than 2 Gyr (possibly even as old as 10 Gyr) and remain gas-rich because their
star formation rates (SFRs) have been very low (< 10^{-3} M_{sun}/yr)
throughout. In such systems, star formation (SF) appears to have been sporadic
and local, though one object (HIPASS J1321--31) has a peculiar red plume in its
CMD suggesting that many of its stars were formed in a "miniburst" 300 - 500
Myr ago. The question of why there are no similar dwarf galaxies in the Local
Group remains open.
