Not really a moss, Riccia is more primitive than that being about half a billion years old - it's a "Liverwort" commonly known as "Crystalwort". "Wort" was a more primitive name for a plant, hence other plants named "bladderwort" and "lungwort".

Mosses and Liverworts are both Bryophytes, but are different:
http://www.majordifferences.com/2014/04/difference-between-liverworts-and-mosses.html

See also:
Botany 321 - Mosses and Liverworts, UBC 2001.
http://www3.botany.ubc.ca/bryophyte/index.html

Exclusive conservation of mitochondrial group II intron nad4i548 among liverworts and its use for phylogenetic studies in this ancient plant clade
http://onlinelibrary.wiley.com/doi/10.1111/j.1438-8677.2011.00499.x/full