Family LARCOSPIRIDAE Haeckel, 1887 n. stat.

Larcospirida Haeckel, 1887: 691, 695 [as a subfamily]. — Schröder 1909: 57 [as a subfamily].

Soreumida Haeckel, 1882: 464 [nomen dubium, as a subfamily]; 1887: 604, 712 [as a family]. — Schröder 1909: 4, 62 [as a family]. — Anderson 1983: 25 [as a family].

Streblacanthida Haeckel, 1887: 704 [as a subfamily]. — Schröder 1909: 60 [as a subfamily].

Streblopylida Haeckel, 1887: 704 [as a subfamily]. — Schröder 1909: 60 [as a subfamily].

Larcopylida Dreyer, 1889: 48 [as a family].

Soreumatidae – Poche 1913: 210 [nomen dubium]. — Campbell 1954: D100. — Blueford 1988: 254.

Larcopylidae – Poche 1913: 210. — Chen & Tan 1996: 152. — Tan 1998: 247. — Tan & Chen 1999: 239. — Chen et al. 2017: 149.

Soreumidae [sic] – Clark & Campbell 1942: 51 [nomen dubium] (= Soreumatidae); 1945: 28. — Chediya 1959: 161. — Tan & Tchang 1976: 267.

Larcopylinae – Campbell 1954: D96.

Larcospirinae – Campbell 1954: D100. — Chediya 1959: 159. — Tan & Tchang 1976: 264. — Tan 1998: 280. — Tan & Chen 1999: 265. Streblopylinae – Campbell 1954: D100.

Tholospira [sic] – Tochilina 1985: 98 (= Tholospiridae).

TYPE GENUS. — Larcospira Haeckel, 1887: 695 [type species by subsequent designation (Campbell 1954: D100): Larcospira quadrangula Haeckel, 1887: 696].

INCLUDED GENERA. — Larcospira Haeckel, 1887: 695 (= Larcospirema with the same type species). — Pylospira Haeckel, 1887: 697 (= Pylospirema with the same type species). — Streblacantha Haeckel, 1887: 706 (= Spironetta n. syn., Spironium n. syn., Streblopyle n. syn.). — Tholospira Haeckel, 1887: 699 (= Tholospirema with the same type species; Larcopyle synonymized by Tochilina 1985: 99; Stomatodiscus n. syn.; Tholospironium synonymized by Popofsky 1912: 152).

NOMINA DUBIA. — Drymospira, Larcospironium, Pylospironium, Soreuma, Soreumidium, Soreumium, Sorolarcidium, Sorolarcium, Sorolarcus, Spironilla .

DIAGNOSIS. — A Spirally growing skeleton with a medullary shell of Zonariidae type ( Tetrapyle) consisting of a microsphere, an antapical sagittal arch and two lateral symmetrical arches originating from the apical part of the microsphere and the top of the sagittal arch. Protoplasm is observed in the Larcopyle -form of Tholospira and Larcospira . Protoplasm fills the shell except but not the outermost peripheral region. Algal symbionts in Larcopyle -form of Tholospira are scattered inside the cortical shell.

STRATIGRAPHIC OCCURRENCE. — late Middle Eocene-Living.

REMARKS

The internal skeletal structure for Larcopyle -form of Tholospira was already documented (Dumitrica 1989: pl. 15, figs 2, 3; Yamauchi 1986: pl. 1, fig. 18) and Larcospira (Sugiyama et al. 1992: pl. 9, fig. 1-5). A “pylome” was detected in the Larcopyle - and Stomatodiscus -forms of Tholospira, but it consists of a simple aperture without discrete margins (Barwicz-Piskorz 1999: figs 3.H-3J). There is often misidentification of the “ Spireuma ” form of Lithelius (Litheliidae) and Tholospira (Larcospiridae) due to their similar spiral appearance, but the Litheliidae are fundamentally different from the Larcospiridae as the former bear a spherical microsphere and do not have S1a-girdle, G1 and G2, girdle structures. Protoplasm and algal symbionts were documented in the Larcopyle -form of Tholospira (Zhang et al. 2018: 14, fig.11, p. 19, fig. 7) and Larcospira (Zhang et al. 2018: 11, fig. 20) using DAPI dyeing epi-fluorescent techniques.

VALIDITY OF GENERA

Streblacantha

Spironium has the same type species as Spironetta . The spiral appearance of Spironium has already been proved as an “artificial torsional” appearance of Larcospira by computer simulation (Ogane & Suzuki 2009: figs 3 and 4), but this doubtless geometric principle did not apply to the Atlas in time. This is the reason why Spironium is synonymized with Streblacantha . The supporting image of Streblopyle for the Atlas is conspecific with that of Pylospira, but this also failed to be fixed in the Atlas due to time limitation.

Tholospira

Identification of “larcopylids” and “lithelids” has been discussed from the anatomical point of views (Tochilina 1985: 95-101), practical usages (Lazarus et al. 2005 97-106; Suzuki et al. 2009d: 248-251; Matsuzaki et al. 2015: 29) and intraspecies variations and evolution (Tochilina & Vasilenko 2018a: fig. 6, pls 10-13). Lazarus et al. (2005) artificially put any larcopylids and lithelids into a single genus Larcopyle and Suzuki et al. (2009d) as the single genus Lithelius . These artificial treatments are not needed any longer because Larcopyle and Lithelius are completely different in their molecular phylogenetic positions (Ishitani et al. 2012; Sandin et al. 2021) as well as their evolutionary changes (Tochilina & Vasilenko 2018a). Our Atlas first visualized the detailed internal structure of Tholospira in Nomarski microscopy with the help of OKU Osamu, a professional of optical microscopy (supporting image for Stomatodiscus in the Atlas). These images are sufficient to recognize the same internal structures among Larcopyle, Stomatodiscus, Tholospira and Tholospironium . Tholospira was defined by simple spiral turns and Tholospironium by double spiral turns (Campbell 1954: D100), but the real specimen for Tholospira (the supporting image in the Atlas) looks to have double spiral turns and the topotypical specimen of Tholospironium from the H.M.S. Challenger Station 271 (Zhang & Suzuki 2017: figs 17.1, 17.2) looks as a simple spiral turn. Appearance of spiral turns depends on the orientation of the specimens. Stomatodiscus is defined by a disc shape with two openings (Campbell 1954: D92), but both sides of the shell are open in the young growing stages of them (Zhang & Suzuki 2017: figs 18.1-18.22). Zhang & Suzuki (2017) published the first paper to practically synonymize “ Stomatodiscus ” with Tholospira ( Larcopyle in original). Tholospira is the oldest available name among them.