Centrohelea Kühn 1926
Diagnosis: Non-flagellate heliozoa with axopodial axonemes; nucleus eccentric; centrosome central; two types of siliceous scales present ancestrally (flat inner tangential plate scales and elongated, usually pointed, outer radial spine scales), but outer scales or both scale layers secondarily lost in several derived lineages.
Because the scales are poorly visible by light microscopy, the most exact method for identification of centrohelids is the Scanning Electron Microscope. SEM is a traditional method for examining the ultrastructure of centrohelidian scales. This method provides high quality images of spine and plate scales and so it is applied for taxonomic descriptions of centrohelidian species.
| Included families (key should be updated): | |||||
| 1 | Periplast composed of siliceous scales |
2 |
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| – | Periplast without siliceous elements | 5 | |||
| 2 | Periplast with tangential rod-shaped spicules or plates | Raphidiophryidae | |||
| – | Periplast wit tangential plates and radial spicules | 3 | |||
| 3 | Radial spicules with centrally attached basal plate | Acanthocystidae | |||
| – | Radial spines without such a plate | 4 | |||
| 4 | Radial spines with winglike structures | Pterocystidae | |||
| – | Radial spines with eccentrically attached basal plate | Choanocystidae | |||
| 5 | 18S rRNA short | Heterophryidae | |||
| – | 18S rRNA markedly longer | Marophryidae | |||