Polyentactinia zhamoidai, from Afanasieva et al. (2005).

Belongs within: Radiozoa.
Contains: Spongentactiniidae, Spongopolyentactiniidae, Haplentactiniidae.

The Spumellaria are a major group of radiolarians with a spongy or porous skeleton (Afanasieva et al. 2005).

Radiolarians of the globe
Published 9 January 2019

Radiolarians are one of the primary groups of micro-organisms to be found among the marine plankton. These unicellular greeblies are justly famed for their intricate mineralised skeletons, leading to their comparison to living works of art. This page covers one particular group of radiolarians, the Spumellaria.

Haeckel’s (1899–1904) figure of Hexancistra quadricuspis from Kunstformen der Natur.

Spumellaria are one of the major subdivisions of radiolarians, containing species characterised by a generally spherical skeletal form. Many authors have also included the colonial radiolarians, which often lack a coherent skeleton and may form colonies up to several metres long, in the Spumellaria but these have more recently been treated as a distinct group. The skeleton of radiolarians is entirely enclosed by cytoplasm in life, though in those species in which the skeleton bears radiating spines, those spines may extend beyond the main body of the cell and be covered by only a thin cytoplasmic layer distally. In Spumellaria and anothre major radiolarian group, the Nassellaria, the skeleton is composed of opal, making these living jewels in more ways than one (another radiolarian group, the Acantharea, composes its skeleton of a mineral by the somewhat ethereal-sounding name of celestite). The cytoplasm of radiolarians is internally divided by a fibrous capsule into two structurally distinct sections, the internal endoplasm and external ectoplasm. The denser endoplasm contains most of the cell’s primary organelles, such as the nucleus and large mitochondria. Linear microtubular structures called axonemes extend outwards from the endoplasm, passing through pores in the internal capsule and through the ectoplasm. The ectoplasm is often frothy in texture, containing an extensive assemblage of cellular vacuoles. In many of these radiolarians, some of these ectoplasmic vacuoles will house symbiotic algae that contribute much of the radiolarian’s nutrition. Otherwise, radiolarians may feed on other small organisms that are captured on axopodia supported by the axonemes, which in spumellarians radiate outwards from the cell body in all directions. Extension and contraction of the axopodia may also help maintain the radiolarian’s position in the water column (Cachon et al. 1990).

Schematic diagram of organisation of Didymocyrtis tetrathalamus from Sugiyama & Anderson (1998).

In many spumellarians, the basic skeletal architecture is one of nested spheres and/or globules. Sugiyama & Anderson’s (1998) description of Didymocyrtis tetrathalamus stands as a fairly typical example. The central part of the skeleton is a double sphere well within the cytoplasmic capsule with the lobate nucleus contained in the spaces between the spheres. Radiating axes connect the inner shell with an outer shell mostly just outside the capsule (the capsular wall crosses the skeleton at some points). In Didymocyrtis, this outer shell is not spherical but a sort of peanut shape. At each end of the ‘peanut’, a further cap is added beyond the main shell. In many spumellarians, the outer shell appears spongy in texture, being constructed of densely criss-crossing fine opal fibres. There may be further extensions of the outer shell such as polar spines or funnels.

Not surprisingly, spumellarian classification has most commonly been based on skeletal architecture. Some attempts have been made to construct alternative classifications incorporating cytoplasmic features such as the relationship between the axopods and the nucleus (Cachon et al. 1990) but, as these systems require access to live specimens to place taxa, they have been less popular (especially as most people studying radiolarians are primarily working with fossil material). A phylogenetic study of recent spumellarians by Ishitani et al. (2012) found evidence for two main lineages within the class that differ in ecology. One, including the families Pyloniidae and Sponguridae, contained species found in temperate and cold waters. The other, including the families Astrosphaeridae, Hexalonchidae and Coccodiscidae, was found in tropical waters. Species assigned to the family Spongodiscidae were divided between both lineages, suggesting the need for some further tinkering with the morphological classification.

Systematics of Spumellaria

Characters (from Afanasieva et al. 2005): Homoaxonic, radially-rayed, with spherical latticed, reticular, or spongy skeleton and inner frame in shape of spicule or microsphere.

<==Spumellaria [Spumellarida]
    |    |--SpongentactiniidaeAA05
    |    `--SpongopolyentactiniidaeAA05
         |    |--Busuanga Yeh 1990AA05
         |    |--Lobactinocapsa Dumitrica 1978AA05
         |    |--Pentactinocapsa Dumitrica 1978AA05
         |    |--Pentactinorbis Dumitrica 1978AA05
         |    `--Pentactinocarpus Dumitrica 1978AA05
         |         `--P. tetracanthusAA05
            |    |--Orodapis Friend & Riedel 1967AA05
            |    |--Orosphaera Haeckel 1887AA05
            |    |--Orostaurus Friend & Riedel 1967AA05
            |    `--Oropelex Friend & Riedel 1967AA05
            |         `--O. pagodaAA05
            |    |--Magnisphaera Won 1997 [Magnisphaerinae]AA05
            |    `--PolyentactiniinaeAA05
            |         |--Cuboctostylus Bragina 1999AA05
            |         |--Pyloctostylus Dumitrica 1994AA05
            |         `--Polyentactinia Foreman 1963AA05
            |              |--P. circumretiaAA05
            |              |--P. kossistekensisAA05
            |              `--P. zhamoidaiAA05
                 |  |    |--Empirea Whalen & Carter 1998AA05
                 |  |    `--Quinquecapsularia Pessagno 1972AA05
                 |  |         `--Q. spinosaAA05
                 |  `--RhizosphaeridaeAA05
                 |       |--Elatommura Haeckel 1887AA05
                 |       |--Haliomma Haeckel 1860AA05
                 |       |--Haliommilla Haeckel 1887AA05
                 |       `--Rhizosphaera Haeckel 1860AA05
                      |--Arachnostylus Hollande & Enjumet 1960AA05
                      |--Arcicubulus Dumitrica 1983AA05
                      |--Centrocubus Haeckel 1887AA05
                      |--Diplospongus Mast 1910AA05
                      |--Excentroconcha Mast 1910AA05
                      |--Gonosphaera Jørgensen 1905AA05
                      |--Heptacladus Dumitrica, Kozur & Mostler 1980AA05
                      |--Lonchosphaera Popofsky 1908AA05
                      |--Octodendron Haeckel 1887AA05
                      |--Pessagnulus Dumitrica 1983AA05
                      |--Solicubulus Dumitrica 1983AA05
                      |--Welirella Dumitrica, Kozur & Mostler 1980AA05
                      |--Weverisphaera Kozur & Mostler 1981AA05
                      `--Stauropylissa Dumitrica 1989AA05
                           `--S. spongoidalisAA05
Spumellaria incertae sedis:
  Callela Won 1983WBN02
  Streblacantha Dreyer 1889BC98, AA05
    `--S. circumtexta (Jørgensen 1900)BC98
  Anomalocantha dentata (Mast 1910)BC98
  Spirema Haeckel 1887BC98, AA05
    `--S. haliomma (Ehrenberg 1861)BC98
  Styptosphaera Haeckel 1881BC98, AA05
    `--S. spumacea Haeckel 1887BC98
  Antygopora Maletz & Bruton 2005 [Antygoporidae]MB07
    |--*A. ordovicica Maletz & Bruton 2005MB07
    |--A. bella Maletz & Bruton 2007MB07
    |--A. compacta Maletz & Bruton 2007MB07
    |--A. labyrinthina Maletz & Bruton 2007MB07
    `--A. microspina Maletz & Bruton 2007MB07

*Type species of generic name indicated


[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.

[BC98] Bjørklund, K. R., G. Cortese, N. Swanberg & H. J. Schrader. 1998. Radiolarian faunal provinces in surface sediments of the Greenland, Iceland and Norwegian (GIN) Seas. Marine Micropalaeontology 35: 105–140.

Cachon, J., M. Cachon & K. W. Estep. 1990. Phylum Actinopoda. Classes Polycystina (=Radiolaria) and Phaeodaria. In: Margulis, L., J. O. Corliss, M. Melkonian & D. J. Chapman (eds) Handbook of Protoctista. The structure, cultivation, habitats and life histories of the eukaryotic microorganisms and their descendants exclusive of animals, plants and fungi. A guide to the algae, ciliates, foraminifera, sporozoa, water molds, slime molds and the other protoctists pp. 334–346. Jones & Bartlett Publishers: Boston.

Ishitani, Y., Y. Ujiié, C. de Vargas, F. Not & K. Takahashi. 2012. Two distinct lineages in the radiolarian order Spumellaria having different ecological preferences. Deep-Sea Research II 61–64: 172–178.

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

Sugiyama, K., & O. R. Anderson. 1998. Cytoplasmic organization and symbiotic associations of Didymocyrtis tetrathalamus (Haeckel) (Spumellaria, Radiolaria). Micropaleontology 44 (3): 277–289.

[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.

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