PYLODISCIDAE Haeckel, 1887

Family PYLODISCIDAE Haeckel, 1887 sensu Dumitrica (1989)

Pylodiscida Haeckel, 1887: 409, 561-563 [as a family]. — Bütschli 1889: 1963 [as a family]. — Schröder 1909: 3 [as a family]. — Anderson 1983: [as a family].

Triopylida Haeckel, 1887:563 [nomen dubium, as a subfamily].

Hexapylida Haeckel, 1887: 563, 567 [nomen dubium, as a subfamily].

Discopylida Haeckel, 1887: 563, 571 [as a subfamily]. — Dreyer 1889: 38 [as a subfamily].

Pylodiscidae – Popofsky 1908: 225; Popofsky 1912: 142-143. — Clark & Campbell 1945: 24. — Campbell 1954: D92. — Chediya 1959: 144. — Tan & Su 1982: 156. — Dumitrica 1984: 102. — Chen & Tan 1996: 151. — Tan 1998: 232. — Tan & Chen 1999: 226-227. — Chen et al. 2017: 143.

Discopylinae – Clark & Campbell 1945: 25. — Campbell 1954: D93. — Chediya 1959: 145.

Pylodiscinae – Campbell 1954: D92. — Dumitrica 1989: 261. — De Wever et al. 2001: 152-153. — Afanasieva et al. 2005: S286. — Afanasieva & Amon 2006: 129.

Triopylinae – Campbell 1954: D92 [nomen dubium]. — Chediya 1959: 144.

Hexapylinae – Chediya 1959: 145 [nomen dubium].

TYPE GENUS. — Pylodiscus Haeckel, 1887: 570 [type species by subsequent designation (Campbell 1954: D92): Pylodiscus triangularis Haeckel, 1887: 570].

INCLUDED GENERA. — Pylodiscus Haeckel, 1887: 570 (= Pylolena synonymized by Zhang & Suzuki 2017: 25; Discopyle n. syn., Discozonium n. syn., Triodiscus n. syn., Triolena n. syn.,? Trilobatum n. syn.). — Sphaeropylolena Zhang & Suzuki, 2017: 38.

NOMINA DUBIA. — Hexapyle, Triopyle.

DIAGNOSIS. — Larcospiroidea with a three-ray first system (medullary shell) derived from the bifurcation of the antapical Tetrapyle - type sagittal arch. The following systems repeat the aforementioned or change the growth mode.

The protoplasm is well documented in Sphaeropylolena. The endoplasm fills the shell but not its outer part. An ectoplasmic membrane wraps the entirety of the skeleton, including the spines. No algal symbionts were detected.

STRATIGRAPHIC OCCURRENCE. — Late Miocene-Living.

REMARKS

Recognition of the pylodiscid-type triangular center is key differentiating this family from the Larcospiridae. In the Pylodiscidae, the triangular center forms an isosceles triangle (De Wever et al. 2001: 153, fig. 90.2). The isosceles triangle is determined by the presence of three gates (the apertures formed by the lateral views of three girdles) and the surface view of other three girdles (that have an arm-like appearance). Some genera in the Larcospiridae (e.g., the Larcopyle -form of Tholospira) also show an isosceles triangle center in some illustrations (Zhang & Suzuki 2017: 12, figs 5.4). The noticeable visible difference between the Pylodiscidae and Larcospiridae is the position of the microsphere (S1a). The microsphere is always located on the base line of the isosceles triangle in the Pylodiscidae whereas it is always situated in the center of the isosceles triangle in the Larcospiridae. The internal skeletal structure of Pylodiscus (Dumitrica 1989: pl. 15, figs 1, 4-6; Takahashi 1991: pl. 23, fig. 7) and Sphaeropylolena (van de Paverd 1995: pl. 59, fig. 2) was illustrated. Protoplasm and algal symbionts have been already documented by epi-fluorescent observation with DAPI dyeing in Sphaeropylolena (Zhang et al. 2018: 17, fig. 11). In certain cases, Sphaeropylolena was found to be infected with the Marine Alveolata Group I (Ikenoue et al. 2016).

VALIDITY OF GENERA

Pylodiscus

The same morphological terminology used for the Amphitholidae is also applicable for the Pylodiscidae with a few modifications. The G1-mode girdle turns vertically to the equatorial plane (the Fr-plane in Zhang & Suzuki 2017: fig. 4), the G2-mode girdle turns sideways to the Fr-plane so as to connect the adjacent G1-mode girdles, and the G3-mode girdle developed in a parallel to the Fr-plane in order to cover the gate formed by the G2-mode girdle. The Pylodiscidae sensu Campbell (1954) are divided into the Triopylinae (Triodiscus and Triolena as available name) with two pseudo-concentric shells, the Pylodiscinae with three pseudo-concentric shells (Pylodiscus and Pylolena), and the Discopylinae (Discopyle and Discozonium) with four pseudo-concentric shells (Campbell 1954: D92-93). Each subfamily is subdivided into three geometric genera by the G1-mode form (Pylolena, Triolena), the G2-mode form (Triodiscus, Discozonium), and the G3-mode form (Pylodiscus, Discopyle). The visualized ontogenetic growth of Pylodiscus indicates that all these six genera are named for different ontogenetic modes (Zhang & Suzuki 2017: fig. 15). Trilobatum is defined by a triparted-lobular central chamber and solid radial spines on the shell margin (Campbell 1954: D92). This triparted-lobular central chamber looks similar to the G1-mode with the two pseudo-concentric shells but exact anatomical studies have not been carried out for this genus. All the available genera except Trilobatum were simultaneously published in Haeckel (1887). In respect to Zhang & Suzuki (2017), Pylolena is validated among them.