Haeckel, 1862, emend. Sanfilippo and Riedel, 1980
Solitary species with latticed or spongy spherical, subspherical, or ovoid shells (not lenticular); with or without medullary shells. Surface of shell is often covered with spines, but not tubes. All actinommids posses either single or multiple, concentric spherical or ovoid shells. When several shells are present they are connected to each other by radial beams which pierce the cell.
An enormous variety of forms was described in this family whose identification has traditionally been based on Haeckel's (1887) system. Haeckel based the classification of the actinommids (= Suborder Sphaeroidea, exclusive of the Family Collosphaeridae) on the following characters (in decreasing order of importance; see classification of Sphaeroidea):
1. Number of primary radial spines;
2. Number of concentric spheres;
3. Position of concentric spheres (intra- or extracapsular), type and relative size of spines, presence of by-spines, type of medullary shell, etc.).
However, the number of primary spines varies intraspecifically, whereas the number of main concentric spheres, which within some bounds might indeed be species-specific (Riedel and Sanfilippo, 1986), can only be used in the case of fully-grown individuals. It is quite obvious that, based on this trait, Haeckel (as well as many other authors) assigned new names to growth stages still missing the outermost sphere(s) (see classification of Sphaeroidea). Furthermore, while growth of an actinommid as far as we know proceeds from the center toward the periphery (see stages of growth in skeletons), dissolution works in the opposite direction, innermost, more delicate shells usually disappearing before the more robust cortical ones. Thus, materials from the sediments offer yet another suite of "new species", this time missing the medullary (rather than the cortical) shells.
The following species of this family are treated in the present volume (arranged in two groups, according to the aspect of the outermost shell, either latticed or spongy):
[1] Outermost shell spongy [e.g. Plegmosphaera entodictyon]
Spongodictyon spongiosum
Octodendron cubocentron
Plegmosphaera entodictyon
Plegmosphaera exodictyon
Plegmosphaera pachyplegma
Spongoplegma antarcticum
Spongoplegma rugosa
Spongosphaera streptacantha
Styptosphaera spumacea
[2] Outermost shell latticed [e.g.Actinomma sol 2]
Acanthosphaera actinota
Acanthosphaera dodecastyla
Acanthosphaera pinchuda
Actinomma antarcticum
Actinomma arcadophorum
Actinomma leptodermum
Actinomma sol
Arachnosphaera myriacantha
Astrosphaera hexagonalis
Carposphaera acanthophora
Cenosphaera spp.
Centrocubus cladostylus
Cladococcus cervicornis
Cladococcus megaceros
Cromyechinus antarctica
Cromyechinus icosacanthus
Cromyomma circumtextum
Druppatractus irregularis
Heliaster hexagonium
Heliosoma echinaster
Hexacontium aristarchi
Hexacontium armatum/hostile
Hexacontium laevigatum
Saturnalis circularis
Stylatractus spp.
Stylosphaera melpomene
Stylosphaera spumacea
Thecosphaera inermis