TREMATODISCIDAE Haeckel, 1862

Family TREMATODISCIDAE Haeckel, 1862

sensu Suzuki emend. herein

Trematodiscida Haeckel, 1862: 240, 485, 491 [as a tribe]; Haeckel 1882: 459 [as a tribe]; Haeckel 1887: 484, 491 [as a subfamily]. — Mivart 1878: 176. — Stöhr 1880: 107 [as a family]. — Schröder 1909: 42 [as a subfamily].

Discospirida Haeckel, 1862: 240, 485, 513 [as a tribe]. — Zittel 1876-1880: 124 [rank unknown]. — Mivart 1878: 176 [as a subsection]. — Stöhr 1880: 113 [as a family].

Porodiscida Haeckel, 1882: 459 [junior homonym, as a subfamily]; Haeckel 1887: 409, 481-485 [as a family]. — Wisniowski 1889: 685 [as a family]. — Bütschli 1889: 1961 [as a family]. — nec Rüst 1892: 166 [as a family]. — Anderson 1983: 24 [as a family].

Stylodictyida Haeckel, 1882: 459 [as a tribe]; Haeckel 1887: 484, 503 [as a subfamily]. — Schröder 1909: 42 [as a subfamily].

Stylocyclida Haeckel, 1887: 458, 461.

Spongophacida Haeckel, 1882: 461 [nomen dubium, as a tribe]. — Dunikowski 1882: 190 [as a tribe]. — Haeckel 1887: 575 [as a subfamily]. — Schröder 1909: 50 [as a subfamily].

Porodiscidae – Popofsky 1908: 222 [junior homonym]; 1912: 127. — Clark & Campbell 1942: 41; 1945: 23. — Campbell & Clark 1944a: 24; 1944b: 15. — Orlev 1959: 444. — Chediya 1959: 132. — Kozlova 1967: 1171-1173 (sensu emend.). — Petrushevska- ya & Kozlova 1972: 524-525 (sensu emend by Kozlova). — Tan & Tchang 1976: 242. — Riedel & Sanfilippo 1977: 865. — Dumitrica 1979: 24-25; 1984: 102. — Tan & Su 1982: 152. —Anderson 1983: 39. — Blueford 1988: 250. — Chen & Tan 1996: 151. — Hollis 1997: 53. — Tan 1998: 209. — Tan & Chen 1999: 208. — Amon 2000: 41. — Chen et al. 2017: 138.

Trematodiscinae – Clark & Campbell 1942: 41; 1945: 23. — Campbell & Clark 1944a: 24; 1944b: 15. — Frizzell & Middour 1951: 23. — Chediya 1959: 133. — Kozur & Mostler 1978: 128. — Tan & Su 1982: 152. — Tan 1998: 209. — Tan & Chen 1999: 208.

Stylodictyinae – Clark & Campbell 1942: 42; Clark & Campbell 1945: 23. — Campbell & Clark 1944a: 25; 1944b: 16. — Campbell 1954: D92. — Chediya 1959: 134. — Tan & Tchang 1976: 242. — Kozur & Mostler 1978: 128. — Tan & Su 1982: 153. — Tan 1998: 210. — Tan & Chen 1999: 210. — Chen et al. 2017: 141.

Spongophacinae – Clark & Campbell 1942: 47 [nomen dubium]; Clark & Campbell 1945: 25. — Campbell & Clark 1944a: 27;— Campbell & Clark 1944b: 18. — Chediya 1959: 146.

Trematodiscidae – Frizzell & Middour 1951: 23. — Kozur & Mostler 1978: 127.

Stylocycliinae – Campbell 1954: D82.

Flustrellinae Campbell, 1954: D88-89.

Stylocyclinae [sic] – Chediya 1959: 129 (= Stylocycliinae). — Kozur & Mostler 1972: 46.

Amphibrachiinae Pessagno, 1971a: 20 [nomen dubium].

Stylodictyidae – Petrushevskaya 1975: 576.

Spongostaurinae Kozur & Mostler, 1978: 157-159 [nomen dubium].

TYPE GENUS. — Trematodiscus Haeckel, 1861b: 841 [type species by subsequent designation (Frizzell & Middour 1951: 24): Trematodiscus orbiculatus Haeckel, 1862: 492] = junior subjective synonym of Flustrella Ehrenberg, 1839: 90 [type species by monotypy: Flustrella concentrica Ehrenberg, 1839: 132].

INCLUDED GENERA. — Flustrella Ehrenberg, 1839: 90 (nec Gray, 1848) (= Centrospira, Discospirella, Trematodiscus synonymized by Kozur & Mostler 1978: 128; Perichlamydium synonymized byOgane et al. 2009a: 86; Perispirella n. syn., Stylochlamyum n. syn.). — Staurospira Haeckel, 1887: 507 (= Staurodictyon synonymized by Petrushevskaya & Kozlova 1972: 525; Tholodiscus n. syn., Xiphospira n. syn.). — Stylodictya Ehrenberg, 1846: 385 (= Stylodictyon with the same type species; Stylochlamydium n. syn., Stylochlamys n. syn., Stylospongia n. syn.; Stylocyclia synonymized by Müller 1859b: 41; Stylospira synonymized by Haeckel 1887: 513). — Tripodictya Haeckel, 1882: 459 (= Xiphodictyon n. syn.).

NOMINA DUBIA. — Amphibrachium, Spongophacus, Spongostaurus Haeckel, 1882 (nec Swanberg et al., 1985), Spongotripodiscus, Spongotripodium, Spongotripus, Stylodictula, Stylospongidium.

JUNIOR HOMONYMS. — Discospira Haeckel, 1862 (= Discospirella) nec Mantell, 1850; Perispira Haeckel, 1882 (= Perispirella) nec Stein, 1859.

NOMEN NUDUM. — Polydiscus.

DIAGNOSIS. — A spherical microsphere with four decussated radial beams is surrounded by 2 to 20 concentric rings. The ring wall has a variable appearance, ranging from a distinct shape to a very ambiguous shadow. In uncertain identifications, walls are observed in the sectioned specimens. Four, eight, or more non-bladed primary radial beams may be observed.

The endoplasm fills the disc part but does not fill the peripheral gowns or one to three of the peripheral hoops. The central part endoplasm is different from the endoplasm found in the concentric hoops. In these last cases, the U-letter shaped or round bracket-shaped designs are visible on the disk of the concentric hoop parts. The protoplasm sometimes appears as a transparent yellowish-green color under a light microscope, or as a light, bright blue autofluorescent emission after DAPI dyeing under an epi-fluorescent microscope.

No algal symbionts were identified. Ectoplasmic membrane wrapping the skeletal part including the radial spines. In general, a single axoflagellum is observable in living forms but there is no pylome.

STRATIGRAPHIC OCCURRENCE. — Middle Paleocene-Living.

REMARKS

Despite the efforts to resolve the synonymy problem between Flustrella and Porodiscus (Ogane et al. 2009a), this family was classically known as “ Porodiscidae ”. The genus name Porodiscus was proposed for a diatom (Greville 1863), for Polycystinea (Haeckel 1882), and for fungi (Murrill 1903). The genus Porodiscus has been erroneously considered as a primary junior synonym of Trematodiscus (see discussion p. 84-85 in Ogane et al. 2009a), actually there was a long debate on the type species of Porodiscus. Frizzell (in Frizzell & Middour 1951: 24) designates Trematodiscus orbiculatus Haeckel, 1862 as the type species of Porodiscus; later on, Flustrella concentrica Ehrenberg, 1854 (Ehrenberg 1854c) was designated as the type species of Porodiscus (Campbell 1954: D89). However, these seem inappropriate as neither species was among those first subsequently assigned to the genus Porodiscus. Species first subsequently assigned to Porodiscus are: Porodiscus communis Rüst, 1885; P. nuesslinii Rüst, 1885; P. simplex Rüst, 1885. The first attempt to fix the type species of Porodiscus among those first species subsequently assigned to the genus is by De Wever et al. 2001: 158. The Mesozoic revision of genera (O’Dogherty et al. 2009a) revalidate such taxonomic act and considered Porodiscus as an available Mesozoic radiolarian name (but dubium), being Porodiscus communis Rüst, 1885 the type species.

Molecular phylogeny supports a close relationship between Flustrella and Stylodictya. Thus, Stylodictyidae is herein synonymized with Trematodiscidae.Two types of equatorial radial spines were identified as primary radial spines: One type is the spine that is directly connects to the radial beams, the other is the spine that is disconnected from the radial beams. The latter has no value at genus level taxonomy. Ogane et al. (2009a: 84) originally thought that the structure of margarita was different between Flustrella and Stylodictya, but Flustrella in the sense of Ogane et al. (2009a) was tightly connected to Stylodictya stellata and Stylochlamydium venustum in the molecular phylogenetic study and belongs to Clade J (Sandin et al. 2021). According to Ogane et al. (2009a: 86), differences in the internal structure between Flustrella and Perichlamydium are unknown. Considering, these results and newly obtained images in the catalogue, we hereby grouped them together into a single genus.

The taxonomic definition employed hitherto for classical Spongodiscidae could not distinguish Trematodiscidae from the Spongodiscidae in sensu stricto (e.g., De Wever et al. 2001: 158, 160). In particular, their internal structure cannot be identified with normal observation methods. Nonetheless, surface images under scanning electronic microscopes (SEM) provide a clear, perceivable difference between the Trematodiscidae and the Spongodiscidae. The central part observed in several genera of the Trematodiscidae crop out throughout their life. Hoops are generally added one by one, outside the external most hoop on the equatorial plane. The subsequent hoops never cover the previous ones, as such, sutures between hoops remain well visible. Furthermore, external hoops tend to be larger and thicker than inner hoops. Consequently, the center of the disk is thinner than the outer extremities. The observed change in thickness of this disk helps us understand the structure of the Trematodiscidae under a light microscope. These patterns are confirmed by SEM image of the surface in Flustrella (Dumitrica 1973a: pl. 8, figs 1-6; Petrushevskaya 1975: pl. 40, figs 1-4; Nakaseko & Nishimura 1982: pl. 44, figs 1-3; Poluzzi 1982: pl. 20, figs 10-12; Yamauchi 1986: pl. 4, fig. 8; Cheng & Yeh 1989: pl. 1, figs, 15: 18; van de Paverd 1995: pl. 52, fig. 1; Ogane & Suzuki 2006: pl. 1, figs 5-9; pl. 2, figs 1-5; Onodera et al. 2011: pl. 6, figs 1, 2), Staurospira (Suyari & Yamasaki 1988: pl. 3, fig. 9) and Stylodictya (Suyari & Yamasaki 1987: pl. 7, fig. 11). The Trematodiscidae includes morphotypes with “covers” on the faces of the disk. Both “ Spongophacus ” - and “ Perichlamydium ” - forms of Flustrella have two gowns which circumscribe the disk on both faces, though a peripheral slit zone is recognizable in lateral view (Nakaseko & Nishimura 1982: pl. 41, figs 2, 3; pl. 42, figs 1-4; Poluzzi 1982: pl. 21, figs 1-8; Takahashi 1991: pl. 20, fig. 5; van de Paverd 1995: pl. 51, fig. 1; Onodera et al. 2011: pl. 5, figs 15, 16). The degree of coverage of the gown is varies from the peripheral edge, to the entire area of the disk. The Stylochlamydium -form of Stylodictya also tends to become smooth on the surface, as well as a peripheral gown is observed (Onodera et al. 2011: pl. 5, figs 17, 18).

Th internal skeletal structure of Stylodictya was illustrated (Dumitrica 1989: pl. 15, fig. 11). The images of living specimens were identified for the “ Stylochlamydium ” -form of Flustrella (Suzuki & Not 2015: fig. 8.10.6) and Stylodictya (Suzuki & Not 2015: fig. 8.8.13; Matsuoka et al. 2017: appendix A). Protoplasm and algal symbionts were documented by epi-fluorescent observation with DAPI dyeing in the “ Spongophacus ”-form of Flustrella (Zhang et al. 2018: 13, fig. 20, p. 19, fig. 9), the “ Stylocyclia ” -form of Stylodictya (Zhang et al. 2018: 14, figs 6-8, p. 23, fig. 2). Samples fixed with dyeing were shown for Stylocyclia (Aita et al. 2009: pl. 3, fig. 4; pl. 24, fig. 1; pl. 26, fig. 4; pl. 27, fig. 3; pl. 28, fig. 6). Many undescribed genera still remain (e.g., Ogane & Suzuki 2006: pl. 2, figs 8-12).

VALIDITY OF GENERA

Flustrella

The combination of Discospira and Discospirella, and that of Perispira and Perispirella have respectively the same type species. Trematodiscus has already been practically synonymized by Campbell (1954: D89) with all concentric rings forms. Centrospira is defined by a spiral inner ring and outer concentric rings (Campbell 1954: D89-90), Discospirella is characterized by spiral rings (Campbell 1954 as Discospira: D90), Perispirella is characterized by concentric inner rings and outer spiral ones (Campbell 1954 as Perispira: D90). Many illustrations of the Trematodiscidae display the development of a partial ring outside the complete ring (van de Paverd et al. 1995: pl. 52, figs 2, 3, 5, 7), but no photos of spiral development are known to indicate the formation of a ring like that of a spiral foraminifer. These spiral morphologies are intraspecific variations. Perichlamydium is marked by a smooth shell margin with a thin porous equatorial girdle (Campbell: D91-92) and Stylochlamyum is marked by a thin porous equatorial girdle and all rings concentric (Campbell: D92). Equatorial rings develop in later growth stages so that there is no difference at the genus level.

Staurospira

Tholodiscus is characterized by four zig-zag radial lines and the multi-annular outline of the disk (Petrushevskaya & Kozlova 1972: 525) and Xiphospira is defined by the presence of all partly or completely spiral rings and two opposite radial spines (Campbell 1954: D92). The structure of the disk divided by four zig-zag radial lines gives a “decussate” appearance. The zig-zag lines depend obviously on the growth irregularity of each ring part between two “zig-zag radial lines”. The type species of Xiphospira surely shows two radial spines but the type-illustration is a broken specimen in which the other two radial spines are broken off. As the difference between Staurospira and Stylodictya is characterized by the number of solid radial beams or the relevant structure inside the disk (four for Staurospira and more than four for Stylodictya), these three genera (Staurospira, Tholodiscus and Xiphospira) have in common a decussate appearance indicating synonymic relationships. Staurodictyon should be synonymized with Staurospira due to the decussate disk structure. Staurospira, Staurodictyon, and Xiphospira were simultaneously published as subgenera in Haeckel (1887: 504 for Xiphospira, 506 for Staurodictyon, and 507 for Staurospira). Staurospira is validated herein due to a more complete illustration of the type species.

Stylodictya

The combined genera Stylodictya and Stylodictyon, and the combined genera Stylochlamydium and Stylochlamys have respectively the same type species. Sandin et al. (2021) placed “ Flustrella arachnea ” and Stylodictya stellata in the same molecular clade J2 and “ F. arachnea ” and Perichlamydium venustum in clade J1. The criteria at generic level in Sandin et al. (2021) follow those established by Ogane et al. (2009a) who clarified the difference between Flustrella and Stylodictya by examination of the Ehrenberg collection. “ Flustrella arachnea ” is conspecific with Stylodictya arachnea which is also the type species of Stylocyclia. The results obtained by Sandin et al. (2021) likely imply small differences among Stylodictya, Stylocyclia and Stylochlamydium. Stylochlamydium is described as “Like Stylodictya but with thin porous equatorial girdle” and “all concentric rings” (Campbell 1954: D92) but presence of equatorial girdle developed in later growth stage like the Perichlamydium -form of Flustrella. Stylospongia looks like a spongy surface but the type-illustration shows no large difference from Stylodictya arachnea in principal. The oldest available name is Stylodictya.

Tripodictya

This synonymy is tentative. We have never confirmed the occurrence of real specimens similar to Xiphodictyon. Tripodictya is the oldest available name among them.