It's been a couple of good years for radiolarian research! After almost 200 years of studying them, and failing to understand their classification fully (in part thanks to Haeckel honestly), three papers came out in the last 2 years that present molecular data to establish a proper backbone to living radiolarian phylogeny. The first one from last year by Sandin et al. presented a morpho-molecular classification of Nassellarians, then this year a paper by Nakemura et al. sorted out the various groups considered by some to be modern Entactinarians (Entactinaria being an order of polycystines radiolarians known in the Paleozoic and the Mesozoic, primarily), and a preprint by Sandin et al., again, offered a morpho-molecular classification of Spumellarians. Patching them together and adding to that the work from a few years ago by Osamu Takahashi et al. in 2004 which showed that the haeckelian order of Collodaria was in fact highly derived Nassellarians and the work by Biard et al. 2015 which sorted them out, and you get that combined tree (as long as i didn t make any mistakes):

((Eucyrtidoidea, ((Acropyramioidea,((Carpocaniidae, Artostrobioidea),(Acanthodesmoidea,(Orosphaeridae,(Sphaerozoidae,(Collophidiidae,Collosphaeridae))Collodaria)))), (((Archipiloidea,Theopilidae),Plagiacanthoidea), (Cycladophoridae, (Lychnocanoidea,Pterocorythoidea)))))Nassellaria, ((Hexastyloidea, (Spongosphaeroidea,(Lithocyclioidea, Spongodiscoidea))), (Liosphaeroidea,((Rhizosphaeroidea,(Centrocubidae,Excentroconchidae)Centrocuboidea), ((Stylodictyoidea,(Actinommoidea,Spongopyloidea)), (Tholoniidae,Pyloniidae)Pylonioidea))))Spumellaria);
			

Tree of living polycystine radiolarians; after Takahashi et al. 2004, Biard et al. 2015, Sandin et al. 2019, 2020, Nakemura et al. 2020.

The biggest surprises for me in these studies and this tree are:

• the fact that Orosphaeridae are the sister group of the collodarians, and in fact belong to Nassellaria: though honestly, after the fact, it makes so much sense, as an intermediary step!
• the placement of Cannobotryidae inside Plagiacanthoidea: again, make sense, but how is it we never thought about it before? I seem to remember a paper by Maria Petrushevskaya in which she considered them as sister taxa though.

Anyway, now that we have that, we can actually start testing skeletal homology hypothesis and start filling the blanks (given naturally the molecular studies used a very limited number of species/specimens for each group). Very exciting!

References:

Biard, T., Pillet, L., Decelle, J., Poirier, C., Suzuki, N., and Not, F. (2015). Towards an integrative morpho-molecular classification of the Collodaria (Polycystinea, Radiolaria). Protist, 166(3):374– 388.

Nakamura, Y., Sandin, M. M., Suzuki, N., Tuji, A., and Not, F. (2020). Phylogenetic revision of the order Entactinaria—Paleozoic relict Radiolaria (Rhizaria, SAR). Protist, 171(1):125712.

Sandin, M. M., Pillet, L., Biard, T., Poirier, C., Bigeard, E., Romac, S., Suzuki, N., and Not, F. (2019). Time calibrated morpho-molecular classification of Nassellaria (Radiolaria). Protist, 170(2):187–208.

Sandin, M. M., Biard, T., Romac, S., O’Dogherty, L., Suzuki, N., and Not, F. (2020). Morpho-molecular diversity and evolutionary analyses suggest hidden life styles in Spumellaria (Radiolaria). bioRxiv.

Takahashi, O., Yuasa, T., Honda, D., and Mayama, S. (2004). Molecular phylogeny of solitary shell-bearing Polycystinea (Radiolaria). Revue de Micropaléontologie, 47(3):111-118.