1 Abcauline wall of the adnate part of the hydrotheca with transverse striae........................................ 2
- Abcauline wall of the adnate part of the hydrotheca without transverse striae....................................... 7
2 Defensive tubes of the coppinia forming a protective structure over the gonothecae................................. 3
- Defensive tubes of the coppinia not forming a protective structure over the gonothecae........... F. nitidum Watson, 2005
3 Defensive tubes arising amongst the gonothecae. Gonotheca with short distal neck with everted rim.................... 4
- Defensive tubes exclusively on the periphery of the gonothecal mass and arching over the gonothecae................. 5
4 Defensive tubes forming a shield-shaped structure (canopy)............................... F. serratum (Clarke, 1879)
- Defensive tubes simply arching over gonothecae............................. F. magnificum Peña Cantero et al., 2004 b
5 Gonothecae without distal neck................................................. F. antarcticum (Hartlaub, 1904)
- Gonothecae with distal neck............................................................................. 6
6 Coppinia bud-shaped. Gonothecae flask-shaped. Hydrothecal aperture 140–168 µm. Hydrothecal free part 320–420 µm.................................................................................... F. conopeum Watson, 2003
- Coppinia corbula-shaped. Gonothecae irregular. Adnate hydrothecal part short or absent. Hydrothecal aperture 180–250 µm. Hydrothecal free part 650–1875 µm..................................................... F. bouvetensis sp. nov.
7 Gonothecae without juxtaposed walls. Defensive tubes absent................ F. disaggregatum Peña Cantero et al., 1998
- Gonothecae with juxtaposed walls. Defensive tubes present.................................................... 8
8 Hydrothecae and hydrorhiza forming a continuous layer on the substrate.......................................... 9
- Hydrothecae and hydrorhiza spaced and distinct from each other............................ F. serpens (Hassall, 1848)
9 Gonothecae fusiform............................................................. F. adhaerens (Nutting, 1901)
- Gonothecae polygonal....................................................... F. parasiticum (Antsulevich, 1987)