The newly-formed planets hypothesised around XZ Tau B are likely to be super-Earths rather than sub-Earths. This is because the snowline around XZ Tau B is located ~0.5 AU from the host star, which places it well within the central cavity. The snowline is basically the distance from a star where temperatures start to become cool enough in the protoplanetary disk for volatiles such as water to condense into solid ice grains, thereby providing more planet-building material. Forming planets beyond the snowline increases the likelihood for more massive planets.
Osorio et al. (2016), "A Dwarf Protoplanetary Disk around XZ Tau B", arXiv:1606.03118 [astro-ph.SR]