Spongodiscoidea Haeckel 1862

Superfamily SPONGODISCOIDEA Haeckel, 1862

Spongodiscida Haeckel, 1862: 239, 452, 460 [as a tribe]; 1882: 461 [as a subfamily]; 1887: 409, 573-575 [as a family].

Euchitoniilae – Campbell 1954: D86 [as a subsuperfamily].

Spongodiscacea [sic] – Pessagno 1971a: 16, 19 [as a superfamily] (= Spongodiscoidea); 1972: 273, 296 [as a superfamily]; 1973: 50, 56 [as a superfamily]; 1976: 25 [as a superfamily]; 1977b: 930 [as a superfamily]. — Dumitrica 1984: 100 [as a superfamily]. — De Wever et al. 2001: 158.

Spongodiscilae – Pessagno 1971a: 19 [as a subsuperfamily]; 1972: 278 [as a subsuperfamily]; 1973: 50 [as a subsuperfamily]; 1976: 25 [as a subsuperfamily]; 1977b: 930 [as a subsuperfamily].

Spongodiscoidea – Petrushevskaya 1975: 573;Petrushevskaya 1979: 110-111; 1984: 132; Petrushevskaya 1986: 128. — Dumitrica 1979: 25. — Amon 2000: 33. — Bragin 2011: 757-758. — Suzuki et al. 2009d: 251.

Spongodiscata – Afanasieva et al. 2005: S288 [as an order, pars]. — Afanasieva & Amon 2006: 130-131.

DIAGNOSIS. — Flat-shaped Polycystinea with or without, un-walled pylome (excluding Ommatocampe). Radial spines and radial beams emanating from the center to the periphery of disk are absent.

REMARKS

The Spongodiscoidea include the Spongodiscidae (including Clade E2) Euchitoniidae (including Clade E3), Spongobrachiidae and. Panartidae and Spongosphaeridae should also be preferable grouped with these three families according to molecular results (100% PhyML bootstrap values with 10000 replicates and>0.99 posterior probabilities), but we keep morphological (instead molecular) groups as a consensus. Spongodiscoidea in the sense of this catalogue comprise Clades E2 and E3 of Sandin et al. (2021). Not only are these subclades unstable, but representatives of the genus Spongolivella (originally Cypassis) were scattered in Clades E2 and E3.

Molecular phylogenetic studies (e.g., Ishitani et al. 2012; Sandin et al. 2021) clearly revealed that the so-called spongodiscids are divided into three groups at a superfamily level. One group includes Dictyocoryne, Tricranastrum (originally Myelastrum), Spongaster and Spongodiscus, classified in Spongodiscoidea; the second group, the Trematodiscoidea, includes Flustrella; and the third group is formed by Schizodiscus and Spongobrachiopyle, classified in Spongopyloidea. Flat-shaped Polycystinea show a high morphological convergence meaning that an unsophisticated recognition of such a structure as “spongy” or “concentric” leads to a completely false identification and contributes to confusion regarding Spongodiscoidea, Trematodiscoidea and Spongopyloidea. The principal differences among Euchitoniidae, Spongobrachiidae and Spongodiscidae are: 1) a central structure around the spinose microsphere; 2) an ultra-fine structure throughout the shell; and 3) an upcropping condition of the central structure on both polar sides. No simple difference between Spongodiscoidea and Trematodiscoidea is known. The Spongodiscoidea differs from Spongopyloidea by having a walled pylome tube emanating from the microsphere and a disk made of very short parts of discontinuous concentric structures. Trematodiscidae have a microsphere with decussate primary radial beams, exterior concentric hoops which never cover the inner hoops, and four or more straight radial beams originating from the center to the periphery of the disk. A simple way to differentiate the Spongodiscoidea from the Spongopyloidea lies in examining the wall-status of the pylome. The pylome was illustrated in Dictyocoryne (Euchitoniidae) (Matsuoka 1992c: pl. 2, figs 7, 8; 1993b: pl. 1, figs 1, 2; 1994: figs 3.B-3.D, 6.A-6.D), Spongaster (Spongodiscidae) (Matsuoka 1994: fig. 3.B-3.D) and the Pseudocephalis -form of an undescribed genus (Spongodiscidae) (Matsuoka 1994: figs 5.B-5.E).

Many described species cannot be placed into an appropriate genus as many genera of Spongodiscoidea remain undescribed. In particular, “ Spongotrochus glacialis ” which is quite different from any other flat-shaped polycystines (Petrushevskaya 1975: pl. 35, figs 1-6; Nakaseko & Nishimura 1982: pl. 29, figs 1-3; pl. 31, figs 2,3). Other undescribed genera remain in classically established Spongodiscoidea (Jouse 1977: pl. 137, fig. 7; pl. 141, fig. 16; Nakaseko & Nishimura 1982: pl. 32, figs 3; pl. 33, fig. 1; pl. 35, fig. 4).