Pellia moss 
Sold in 125ml cup 
Picture 2 represent a minimum portion size
Picture 1 is a close up of the actual moss for indentification
 
Pelia Moss (Monosolenium Tenerum)

This is not Subwassertang Scientific Name: Lomariopsis sp
 
Pellia
Scientific Name: Monosolenium tenerum
Pellia is a liverwort which can be grown either emersed in a humid environment or submersed in water such as your aquarium. Pellia is an undemanding slow grower & does well in low/high light, all pH ranges, 5-30°C & with or without Co2. Monosolenium tenerum is olive green and has no leaves but rather thallus or thalli(plural). While it will attach itself to objects with fine filaments (rhizoids) on the underside of the thallus or thalli, it freely floats if water current is present. You'll need to tie Pellia to objects if you want them in specific locations in your aquarium. You can also wedge clumps between plants in your aquarium to keep it from floating. It's also fragile & breaks apart easily when handled.
 
While Subwassertang is the gametophyte form of a fern species in the genus Lomariopsis, (possibly lineata) and is not Pellia or a liverwort at all.Subwassertang is often wrongly sold as Pellia, but is definitely not Pellia.Care is very similar as it performs very well in low light. It has no filaments to anchor itself, so it needs to be tied to an object in your aquarium. It's also thinner & lighter green.
 
So... Pellia is thicker & has filaments on the underside and are capable of ataching itself to substate.

Subwassertang is thinner, light green & not as fragile and can not atach itself at all.