Haeckel, 1879
Diagnosis
Siliceous skeleton lacking altogether, or consisting of hollow tubes or foreign objects outside the central capsule either strewn or regularly ordered. The skeletal elements (if present) in these families are loosely associated in the cytoplasm, not united into a fixed structure. The taxonomic relationships among these families needs to be re-examined.
Families treated:
Family Astracanthidae Haecker, 1908
Family Aulacanthidae Haeckel, 1862
Family Phaeodinidae Haeckel, 1879
Family Pharyngellidae Haeckel, 1887