Habitat
Fontinalis antipyretica is always found in aquatic sites. It may be found in moving water attached to rocks and logs, or floating freely in stagnant water.
Gametophyte
Overall Structure:
Fontinalis antipyretica is a large pleurocarpous moss whose dark green, floating or reclining shoots can sometimes exceed a metre in length!
Leaf Structure:
The leaves on a shoot are three-ranked, keeled, and straight. The stem is often red.
The keeled leaves lack a costa (ecostate).
Sporophyte
Sporophytes are rare, however may occur in autumn or spring.
Sporangium:
The mature more or less immersed sporangium is surrounded by leaves and may remain submerged. 
Spore dispersal in an aquatic environment probably obviates the need for a long seta.
A mesh-like structure in the shape of an inverted cone called a trellis is characteristic of the Fontinalis endostome.