  Dilute-gas Bose-Einstein condensates are an exceptionally versatile testbed
for the investigation of novel solitonic structures. While matter-wave solitons
in one- and two-component systems have been the focus of intense research
efforts, an extension to three components has never been attempted in
experiments, to the best of our knowledge. Here, we experimentally demonstrate
the existence of robust dark-bright-bright (DBB) and dark-dark-bright (DDB)
solitons in a spinor $F=1$ condensate. We observe lifetimes on the order of
hundreds of milliseconds for these structures. Our theoretical analysis, based
on a multiscale expansion method, shows that small-amplitude solitons of these
types obey universal long-short wave resonant interaction models, namely
Yajima-Oikawa systems. Our experimental and analytical findings are
corroborated by direct numerical simulations highlighting the persistence of,
e.g., the DBB states, as well as their robust oscillations in the trap.
