Hedriocystis pellucida, bar = 10 µm
Genus Hedriocystis Hertwig & Lesser, 1874
Diagnosis: Cell surrounded by a non-silicious stalked shell; shell hyaline, colorless, with small holes, pores, through which non-branching axopodia radiate; stalk not always distinct, at one species never observed; central nucleus; Schwärmer observed at two species, with one or two flagella.
Type species. Hedriocystis pellucida
Key to the species
| 1 | Stalk longer than the test | 2 |
| – | Stalk shorter than the test | |
| 2 | Shell polygonal and/or with clear conical nipples | |
| – | Shell circular or ovoid in circumference |
Hedriocystis brachypous – from Siemensma 1982