Stauracon pallidus, from Saint-Petersburg State University.

Belongs within: Sar.
Contains: Arthracanthida, Spumellaria, Nassellaria, Aculearia, Sphaerellaria, Stauraxonaria, Collodaria, Archaeospicularia, Entactinaria.

The Radiozoa are a clade of aquatic protists that typically bear mineralised skeletons of silica or strontium sulphate.

Sticholonche zanclea
Published 6 January 2010
Sticholonche zanclea, from here.

Sticholonche zanclea is a very unusual marine protist. In the past, it has been classified among the heliozoans, a group of organisms united by their generally radial arrangement of long cytoplasmic extensions called axopodia. However, both molecular and ultrastructural studies have established that the ‘heliozoans’ are a polyphyletic assemblage of a number of unrelated groups that have converged on a similar morphology. ‘Heliozoans’, in general, are passive trappers of other micro-organisms and food particles by means of their axopodia; the helizoan morphology provides for significant area coverage without massively increasing the cell cytoplasm. Compare this to the ‘radiosa’ form adopted by amoebae that become detached from their substrate and which serves a similar purpose (though in that case the aim is increasing the chance of recontacting the substrate). In the case of Sticholonche, molecular analysis has placed it among the also-axopod-bearing radiolarians with which it shares the production of siliceous spicules. Sticholonche differs from other radiolarians in lacking a central capsule dividing the cell into internal and external sectors; however, said molecular analyses place it nested among rather than sister to radiolarians. Indeed, it may be the sister to the spumellarid family Litheliidae (Kunimoto et al. 2006).

Sticholonche differs from other ‘heliozoans’ in being flattened with the axopodia concentrated laterally. The axopodia are rigid, reinforced by a central core of microtubules, and anchored on small cup-shaped depressions on the nuclear envelope (Cachon et al. 1977). By flexing the nuclear envelope, Sticholonche can move by rowing itself with the axopodia. If your day has so far provided insufficient awesomeness, follow this link, scroll down the page a bit, and you will find a video of a Sticholonche doing just that.

Systematics of Radiozoa

Characters (from Cavalier-Smith 2018): Cells with radiating axopodia supported by axonemes nucleated by one to many intracapsular axoplasts; axonemes of cross-linked microtubules ancestrally in open hexagonal array, each hexagon with 6 (Spasmaria) or 12 microtubules (Polycystinea—in some subgroups hexagons incomplete on one side, resembling branching palisades); axopodia thicker and longer than reticulopodia. Mineralised skeleton usually present: largely strontium sulphate (Acantharea) or amorphous silica (Polycystinea, Sticholonche) with only small amounts of strontium sulphate. Ectoplasm separated from endoplasm by cortical alveoli and dense multiperforated central capsule sandwiched between cortical alveoli and plasma membrane invaginations (Polycystinea) or by extracellular fibrous capsule (Acantharea). Reticulopodia rarely secondarily absent (Sticholonche). Zoospores biciliate.

    |    |--Sticholonche [Sticholonchea, Taxopodida]C-S18
    |    |    `--S. zancleaNB04
    |    `--Acantharea [Acantharia, Acanthariobiontes]C-S18
    |         |--ArthracanthidaAS12
    |         |--HolocanthidaAS12
    |         |    |--AcanthochiasmaAS12
    |         |    |--AcanthocollaAS12
    |         |    `--AcanthoplegmaAS12
    |         |--ChaunocanthidaAS12
    |         |    |--AmphiaconAS12
    |         |    |--ConaconAS12
    |         |    |--GigartaconAS12
    |         |    |--HeteraconAS12
    |         |    `--Stauracon pallidusAS12, BM05
    |         `--SymphyacanthidaAS12
    |              |  i. s.: AmphilithiumAS12
    |              |--PseudolithidaeZSC97
    |              |    |--HaliommatidiumZSC97
    |              |    `--PseudolithiumAS12
    |              `--Astrolonchinae [Astrolonchidae]LT61
    |                   |--AstroloncheAS12
    |                   `--Dipelicophora Loeblich & Tappan 1961 (see below for synonymy)LT61
    |                        `--*D. buetschlii (Schewiakoff 1926) [=*Dicranophora buetschlii]LT61
    `--Polycystinea [Discoidea, Heliosestrinae, Polycystina, Polycystinia]BM05
         |  i. s.: AspiculumidaeMB07
         |           |--Parechidnina Kozur, Mostler & Repetski 1996 [incl. Aitchisonellum Won in Won & Below 1999]MB07
         |           |    |--*P. nevadensis Kozur et al. 1996MB07
         |           |    |--P. aspinosa Won in Won & Below 1999MB07
         |           |    |--P. densa Maletz & Bruton 2007MB07
         |           |    `--P. jamesi Won & Iams 2002MB07
         |           |--Aspiculum Won et al. 2005MB07
         |           `--Nyfrieslandia Maletz & Bruton 2007MB07
         |                |--N. complicata Maletz & Bruton 2007MB07
         |                `--N. sphaeroidea Maletz & Bruton 2007MB07
         |         Haplotaeniatumidae [Haplotaeniatinae]MB07
         |           |--Tetracircinata Nazarov & Ormiston 1984AA05
         |           |--Orbiculopylorum Noble, Braun & McClellan 1998WBN02
         |           |    `--O. marginatum Noble, Braun & McClellan 1998WBN02
         |           |--Labyrinthia Maletz & Bruton 2007MB07
         |           |    `--*L. inexpectata Maletz & Bruton 2007MB07
         |           `--Haplotaeniatum Nazarov & Ormiston 1990AA05
         |                |--*H. labyrintheum Nazarov & Ormiston 1993WBN02
         |                |--H. adobensis (Noble, Braun & McClellan 1998) [=Orbiculopylorum adobensis]WBN02
         |                |--H. aperturatum Noble, Braun & McClellan 1998WBN02
         |                |--H. cathenatum Nazarov & Ormiston 1993WBN02
         |                |--H. primordialis (Rüst 1892)WBN02
         |                `--H. tegimentum Nazarov & Ormiston 1993WBN02
         |         Beothuka Aitchison et al. 1998MB07
         |           `--*B. terranova Aitchison et al. 1998MB07
Radiozoa incertae sedis:
  Scharfenbergia Won 1983WBN02, AA05
    `--S. concentricaWBN02
  Amphiptermis alamedaensisBL79
  Spongotripus Haeckel 1881BL79, AA05
    `--S. morenoensisBL79
  Conosphaera Haeckel 1881BL79, AA05
    `--C. sphaeromaBL79
  Tripilidium Haeckel 1881BL79, AA05
    `--T. dendroacanthosBL79
  Discanthocapsa communisBL79
  Triplococcus acanthicusMB07
  Podactinelius [Actineliida]ZSC97
    `--P. sessilisZSC97

Dipelicophora Loeblich & Tappan 1961 [=Dicranophora Schewiakoff 1926 nec Macquart 1834 nec Schrött. 1886 (ICBN)]LT61

*Type species of generic name indicated


[AS12] Adl, S. M., A. G. B. Simpson, C. E. Lane, J. Lukeš, D. Bass, S. S. Bowser, M. W. Brown, F. Burki, M. Dunthorn, V. Hampl, A. Heiss, M. Hoppenrath, E. Lara, E. Le Gall, D. H. Lynn, H. McManus, E. A. D. Mitchell, S. E. Mozley-Stanridge, L. W. Parfrey, J. Pawlowski, S. Rueckert, L. Shadwick, C. L. Schoch, A. Smirnov & F. W. Spiegel. 2012. The revised classification of eukaryotes. Journal of Eukaryotic Microbiology 59 (5): 429–493.

[AA05] Afanasieva, M. S., E. O. Amon, Y. V. Agarkov & D. S. Boltovskoy. 2005. Radiolarians in the geological record. Paleontological Journal 39 (Suppl. 3): S135–S392.

[BL79] Basov, V. A., B. G. Lopatin, I. S. Gramberg, A. I. Danjushevskaya, V. Ya. Kaban’kov, V. M. Lazurkin & D. K. Patrunov. 1979. Lower Cretaceous lithostratigraphy near Galicia Bank. Initial Reports of the Deep Sea Drilling Project 47: 683–717.

[BM05] Bass, D., D. Moreira, P. López-García, S. Polet, E. E. Chao, S. von der Heyden, J. Pawlowski & T. Cavalier-Smith. 2005. Polyubiquitin insertions and the phylogeny of Cercozoa and Rhizaria. Protist 156: 149–161.

Cachon, J., M. Cachon, L. G. Tilney & M. S. Tilney. 1977. Movements generated by interactions between the dense material at the ends of microtubules and non-actin-containing microfilaments in Sticholonche zanclea. Journal of Cell Biology 72: 314–338.

[C-S18] Cavalier-Smith, T. 2018. Kingdom Chromista and its eight phyla: a new synthesis emphasising periplastid protein targeting, cytoskeletal and periplastid evolution, and ancient divergences. Protoplasma 255: 297–357.

Kunimoto, Y., I. Sarashina, M. Iijima, K. Endo & K. Sashida. 2006. Molecular phylogeny of acantharian and polycystine radiolarians based on ribosomal DNA sequences, and some comparisons with data from the fossil record. European Journal of Protistology 42 (2): 143–153.

[LT61] Loeblich, A. R., Jr & H. Tappan. 1961. Remarks on the systematics of the Sarkodina (Protozoa), renamed homonyms and new and validated genera. Proceedings of the Biological Society of Washington 74: 213–234.

[MB07] Maletz, J., & D. L. Bruton. 2007. Lower Ordovician (Chewtonian to Castlemainian) radiolarians of Spitsbergen. Journal of Systematic Palaeontology 5 (3): 245–288.

[NB04] Nikolaev, S. I., C. Berney, J. F. Fahrni, I. Bolivar, S. Polet, A. P. Mylnikov, V. V. Aleshin, N. B. Petrov & J. Pawlowski. 2004. The twilight of Heliozoa and rise of Rhizaria, an emerging supergroup of amoeboid eukaryotes. Proceedings of the National Academy of Sciences of the USA 101 (21): 8066–8071.

[WBN02] Won, M.-Z., R. B. Blodgett & V. Nestor. 2002. Llandoverian (Early Silurian) radiolarians from the Road River Formation of east-central Alaska and the new family Haplotaeniatumidae. Journal of Paleontology 76 (6): 941–964.

[ZSC97] Zettler, L. A., M. L. Sogin & D. A. Caron. 1997. Phylogenetic relationships between the Acantharea and the Polycystinea—a molecular perspective on Haeckel’s Radiolaria. Proceedings of the National Academy of Sciences of the USA 94: 11411–11416.

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