  We report the discovery of eight optical counterparts of ALFALFA
extragalactic objects from DECaLS, five of which are discovered for the first
time. These objects were flagged as HI emission sources with no optical
counterparts in SDSS before. Multi-band data reveal their unusual physical
properties. They are faint and blue ($g-r=-0.35\sim0.55$), with quite low
surface brightness ($\mu_{\rm g,peak}=24.88\sim26.41\,{\rm mag}/{\rm
arcsec}^2$), irregular morphologies, low stellar masses
($log_{10}(M_{*}/M_\odot)=5.27\sim7.15$), low star formation rates
($SFR=0.21\sim9.24\times10^{-3}\,{M_\odot}\,{\rm yr}^{-1}$), and remarkably
high HI-to-stellar mass ratios ($log_{10}(M_{\rm HI}/M_{*}) = 1.72\sim3.22$,
except AGC\,215415). They deviate from the scaling relations between HI and
optical properties defined by the ALFALFA sample and the baryonic Tully-Fisher
relation. They agree well with the main sequence of star-forming galaxies but
exhibit low star-forming efficiency. Based on their physical properties and
environments, we speculate that six of these objects may have originated from
tidal processes, while the remaining two appear to have isolated origins. They
may have had a relatively calm evolutionary history and only begun to form
stars recently.
