HELIODISCIDAE Haeckel, 1882

Family HELIODISCIDAE Haeckel, 1882 sensu De Wever et al. (2001)

Heliodiscida Haeckel, 1882: 457 [as a tribe]; 1887: 421, 444 [as a subfamily]. — Schröder 1909: 41 [as a subfamily].

Heliodiscinae – Clark & Campbell 1942: 38; 1945: 22. — Campbell 1954: D82. — Chediya 1959: 127. — Kozur & Mostler 1972: 21 (sensu emend.). — Dumitrica 1984: 97-98 (sensu emend.).

Sethodiscinidae Chediya, 1959: 124.

Heliodiscidae – Kozur & Mostler 1972: 18-21 (sensu emend.). — Petrushevskaya 1975: 576. — Dumitrica 1979: 22. — De Wever et al. 2001: 124-125. — Afanasieva et al. 2005: S275. — Afanasieva & Amon 2006: 112. — Vishnevskaya 2006: 137; Matsuzaki et al. 2015: 14.

TYPE GENUS. — Heliodiscus Haeckel, 1862: 436 [type species by subsequent designation (Strelkov & Lipman 1959: 444): Haliomma phacodiscus Haeckel, 1861a: 815].

INCLUDED GENERA. — Actinommura Haeckel, 1887: 255 (=? Excentrosphaerella n. syn.). — Excentrococcus Dumitrica, 1978: 238. — Excentrodiscus Hollande & Enjumet, 1960: 125. — Heliodiscus Haeckel, 1862: 436 (= Heliodiscilla with the same type species; Heliocladus n. syn., Heliodiscetta n. syn., Heliodrymus n. syn.; Heliodendrum, Heliosestilla synonymized byKozur & Mostler 1972: 19). — Helioferrusa Dumitrica, 2019: 52. — Phaenicosphaera Haeckel, 1887: 75 (= Dreyeropyle n. syn.).

INVALID NAME. — Anthomma.

NOMINA DUBIA. — Actinommantha, Astrophacetta, Astrophacus, Astrosestilla, Astrosestomma, Cerasosphaera, Distriactis, Heliodiscura.

DIAGNOSIS. — Flat to spherical shells with an eccentric microsphere, and a spherical to ellipsoid outer medullary shell. Protoplasm illustrated for Heliodiscus. The endoplasm is situated near the double medullary shell and occupies the cortical shell in fully-grown cells. Tens to hundreds of algal symbionts are always found inside the cortical shell. A transparent endoplasm is located in the medullary shell, and this in turn, is enclosed by a reddish endoplasmic cover except on its apical side. The detailed protoplasmic structure is known in Excentrodiscus. In Excentrodiscus, no axopodial system was identified. The nucleus occupies the outer double medullary shell and its lobate parts sometimes extrude through pores of the outer double medullary shell.

STRATIGRAPHIC OCCURRENCE. — Early Eocene-Living.

REMARKS

The Heliodiscidae show some homeomorphy with the Lithocycliidae and Phacodiscidae. Differing from Heliodiscidae, the latter two families do not have an eccentric innermost microsphere. The innermost microsphere appears to be covered by the second outer shell, but the figure shown in van de Paverd (1995: pl. 38, fig. 6) indicates that the heteropolar microsphere extends outwards from the second outer shell. Internal skeletal structure was illustrated for Actinommura (Dumitrica 2019: figs 11.a, 11.b), Excentrococcus (Sugiyama & Furutani 1992: pl. 16, fig. 4; Sugiyama et al. 1992: pl. 7, figs 1, 2; Suzuki 1998b: pl. 7, figs 11-12?; Dumitrica 2019: figs 8.a, 8.c), Excentrodiscus (Dumitrica 2019: figs 9.d-9.g, 10.c), Heliodiscus (Sugiyama et al. 1992: pl. 5, figs 1-8; van de Paverd 1995: pl. 38, fig. 6), Helioferrusa (Dumitrica 2019: figs 9.b, 9.c) and Phaenicosphaera (Sugiyama & Furutani 1992: pl. 16, fig. 3). A living image was illustrated for Heliodiscus (Takahashi et al. 2003: figs 2, 3; Probert et al. 2014: S1, Vil 219). Protoplasm and algal symbionts were documented by epi-fluorescent observation with DAPI dyeing for Heliodiscus (Zhang et al. 2018: 9, fig. 11, p. 11, figs 12, 13, 23; p. 16, fig. 7). Fine protoplasmic structure was illustrated in Excentrodiscus (Hollande & Enjumet 1960: pl. 24, figs 4, 5). Algal symbionts of Heliodiscus were identified as Brandtodinium nutricula by Probert et al. (2014).

VALIDITY OF GENERA

Actinommura

Any specimen fitting with Actinomma capillaceum, the type species of Actinommura, possess a microsphere which is eccentrically located in the outer medullary shell (See the supporting image for Actinommura in the Atlas). This character is exactly the same in Excentrosphaerella, but the type-illustration for A. capillaceum (Haeckel 1887: pl. 29, fig. 6) is drawn with a perfect concentric symmetry to the microsphere. We suspect the quality of this illustration but it has no value to questionably synonymize Excentrosphaerella with Actinommura. Actinommura is an available name older than Excentrosphaerella.

Heliodiscus

The combinations of the following genera have respectively same type species: Heliodiscus and Heliodiscilla, Heliocladus and Heliodrymus, and Heliodendrum and Heliosestilla. The specimens identifiable to Heliodiscus and Heliodendrum (the supporting images for both these genera in the Atlas) have eccentric microspheres, indicating they are members of the Heliodiscidae.

Heliocladus is defined by a smooth surface and no spines on the cortical shell, ten to 20 branched equatorial radial spines and a simple medullary shell (Campbell 1954: D82). Heliodendrum differs from Heliocladus by simple or branched robust spines on the cortical shell surface (Campbell 1954: D82). We have never met forked equal radial spines like in the type species of Heliocladus but the variability in the shape of the equatorial radial rings is commonly observed in the same samples. The development status of robust spines on the cortical shell surface also varies from absent to very robust like the supporting image for Heliodendrum in the Atlas in the same samples. These differences between Heliocladus and Heliodendrum are insufficient for a difference at generic level. The innermost shell of Heliodiscus specimens is easily lost by dissolution so as not to be applied as genus criteria.

Phaenicosphaera

Phaenicosphaera is defined by round, irregular but dissimilar pores on the spherical cortical shell and one medullary shell (Campbell 1954: D48). The translated definition of Dreyeropyle in Kozur & Mostler (1979: 14) from German is “two concentric spherical lattice shells with numerous short main spines. In the area of the large pylome bordered by spines, there are very large pores which are considerably larger than the remaining pores.” The type-illustrations were based from the sketches included in classic papers (Haeckel 1887 for Phaenicosphaera; Dreyer 1889 for Dreyeropyle). However, the drawings of the type species of Phaenicosphaera and Dreyeropyle do not show the eccentric microsphere; but it was probably overlooked because the existence of any eccentric microsphere had never been recognized until Hollande & Enjumet (1960) who erected Excentrodiscus on the basis of the presence of this structure. The most representative real specimens of Carposphaera nodosa for the type species of Phaenicosphaera and of Sphaeropyle heteropora for type species of Dreyeropyle (supporting image of this genus in the Atlas) possess eccentric microspheres in the periphery of the outer medullary shell and more flattened spherical cortical shells. Any specimens which have very large pores like the specimen type illustrated of Dreyeropyle have never been found and reported so far. This highly presumes of the occurrence of exaggerated drawings. The real specimens show no significant differences which could correspond to different genus criteria. Phaenicosphaera is an available name older than Dreyeropyle.