Pylodiscus, Haeckel, 1887

Zhang, Lanlan & Suzuki, Noritoshi, 2017, Taxonomy and species diversity of Holocene pylonioid radiolarians from surface sediments of the northeastern Indian Ocean, Palaeontologia Electronica (Cambridge, England: 2003) 7 (8), pp. 1-68 : 25-26

Genus PYLODISCUS Haeckel, 1887 sensu emend.

nomen dubium

1882 Hexapyle Haeckel , p. 464 (type species: Hexapyle triangula Haeckel ).

nomen dubium

1882 Triopyle Haeckel , p. 464 (type species: Triopyle circulus Haeckel ).

*1887 Pylodiscus Haeckel , p. 570.

1887 Pylolena Haeckel , p. 567 (type species: Pylolena armata Haeckel ).

1887 Hexapyle Haeckel ; Haeckel, p. 568.

1887 Triopyle Haeckel ; Haeckel, p. 565.

1954 Hexapyle Haeckel ; Campbell, p. D92.

1954 Pylodiscus Haeckel ; Campbell, p. D92. 1954 Pylolena Haeckel ; Campbell, p. D72.

1954 Triopyle Haeckel ; Campbell, p. D92.

1979 Hexapyle Haeckel ; Kozur and Mostler, p. 46.

1979 Triopyle Haeckel ; Kozur and Mostler, p. 46. 1979 Pylodiscus Haeckel ; Kozur and Mostler, p. 46.

1979 Pylolena Haeckel ; Kozur and Mostler, p. 46.

ZHANG & SUZUKI: TAXONOMY OF HOLOCENE PYLONIOID

Type species. Pylodiscus triangularis Haeckel, 1887 (SD by Campbell, 1954).

Description. Test is flat and triangular in shape with a central combination and one or two triangular pseudo-concentric shells. The 1st pseudo-concentric shell consists of five girdles. The gates of the two girdles show their tunnel view, and those of the other three girdles show their aperture view in Fr-view in Type 2 coordinates to form a flat, triangular, pseudo-concentric shell. The two gates with aperture view in Fr-view are directly connected with the S1a (microsphere) ( Figure 15.3 ). Thus, the Lt-axis passes through the center of S1a and these two gates. The other gate with aperture view in Fr-view occurs beneath the S1a along the Pl-axis, and the Sg-axis under Type 1 coordinates is therefore equivalent to the Fr-axis of the 1st pseudo-concentric shell in Type 2 coordinates. The 2nd pseudo-concentric shell also has a flat, triangular appearance and is arranged upside-down relative to the 1st pseudo-concentric shell. The Fr-axis of each pseudo-concentric shell is identical to the Sg-axis with Fr-view in the same direction. Latticed cover may develop on both flattened sides of the test in fully mature specimens of some species. Specimens with latticed cover look inflated, and flat triangular in shape.

Remarks. The definition of Pylodiscus has been revised to include all flat triangular pylodiscid species that have pylodiscid 1st pseudo-concentric shells. Species with such morphology have been considered to belong to Hexapyle Haeckel, 1882 , Triopyle Haeckel, 1882 , Pylodiscus Haeckel, 1887 , and Pylolena Haeckel, 1887 . However, species of these genera can be placed into a single genus. The type species of Pylolena , Pylolena armata Haeckel, 1887 , is a younger stage of some species of Pylodiscus that has an incomplete triangular 2nd pseudo-concentric shell. Our definition includes socalled Hexapyle species because of the nomen dubium status of Hexapyle Haeckel, 1882 ( Campbell [1954] designated an un-illustrated species as the type species of this genus). The genus name Hexapyle has been applied in practice with Hexapyle dodecantha Haeckel, 1887 , and Hexapyle spinulosa Chen and Tan, 1990 . These two species are similar to Pylodiscus triangularis Haeckel, 1887 , the type species of Pylodiscus , except for their closed/open gates with latticed cover and the presence/absence of polar-beams in the gates. These differences are inferred to be the results of differences in ontogenetic growth. The genus names Triopyle Haeckel, 1882 , and Pylolena Haeckel, 1887 , are unsuitable for practical use with real specimens because their type species have not yet been illustrated. Triopyle hexagona Haeckel, 1887 , and Pylolena armata Haeckel, 1887 , were illustrated as members of Triopyle and Pylolena , respectively, but these species are now considered to be younger stages of Pylodiscus species.

Figures

FIGURE 15. Photographs of the encountered morphotypes of Pylodiscus spinulosus (Chen and Tan, 1989). All are Fr- view at Type 2. Scale bar equals 0.1 mm. All specimens are from YDY05-01.