SPONGOPYLIDAE Dreyer, 1889

Family SPONGOPYLIDAE Dreyer, 1889 sensu Suzuki emend. herein

Spongopylida Dreyer, 1889: 42 [as a subfamily].

Spongopylinae – Campbell 1954: D94.

Spongopylidae – Kozur & Mostler 1978: 159.

TYPE GENUS. — Spongopyle Dreyer, 1889: 42 [type species by subsequent designation (Campbell 1954: D94): Spongopyle setosa Dreyer, 1889: 43].

INCLUDED GENERA. — Schizodiscus Dogiel in Dogiel & Reshetnyak, 1952: 8. — Spongobrachiopyle Kozur & Mostler, 1978: 160. — Spongopyle Dreyer, 1889: 42 (= Spongopylarium with the same type species). — Spongospira Stöhr, 1880: 120.

NOMEN DUBIUM. — Spiropyle.

DIAGNOSIS. — The central part consists of a pit-like small microsphere directly connected to a tunnel-like pylome. The shell has a flat to simple, convex-lens shape (e. g. Spongopyle and Spongobrachiopyle). Another type is characterized by the lateral profile of the disk showing: 1) a simple convex-lens shape; or 2) an inflated convex-lens shape in the center, thinner zone or a groove outside the central part, as well as a thick peripheral spongy zone (Schizodiscus). A single, walled tunnel-like pylome is extended from, or near, the microsphere. The general spongy structure shows many discontinuous rings having very short radial beams or other fine columnar beams connected between adjacent discontinuous rings. These discontinuous rings and radial beams resemble a “structureless” sponge. This “structureless sponge” is highly dense near the central part and becomes looser away from the center

Protoplasm was reported for Schizodiscus, Spongobrachiopyle and Spongospira, but these characters will be described in the remarks as there are concerns about whether or not they truly belong to the same family. No algal symbionts were found.

STRATIGRAPHIC OCCURRENCE. — Late Eocene-Living.

REMARKS

The independency of the Spongopylidae from the Spongodiscidae was recognized by molecular phylogenic studies (Ishitani et al. 2012). After updating the taxonomic name of Ishitani et al. (2012), Schizodiscus was transferred to Trematodiscidae (originally Stylodictyidae in Matsuzaki et al. 2015: 25). New molecular phylogenetic analysis on more genera and species resulted in the grouping of Schizodiscus and Spongobrachiopyle (originally Spongopyle) into a cluster (Cluster L) independent from the Trematodiscidae (Cluster J). Subsequently, we divided the “Stylodictyidae” of Matsuzaki et al. (2015) into two families: Spongopylidae and Trematodiscidae here.

A typical image of the walled tunnel-like pylome is given in pl. 39, fig. 3b of Nakaseko & Nishimura 1982. Under good conditions, the walled-pylome is distinctive under a light microscope (Kruglikova 1969: fig. 4.29). In identifying the genera of this family, the important points are: (a) the actual density of the “spongious part” with regard to the “thickness effect” under a light microscope, (b) the presence of primary radial beams, (c) the “wall type ” of the pylome, and (d) the zonal structure of the disk from the center to the peripheral zone in relation with the “thickness effect”. The radial spines disconnected from radial beams should be ignored at the genus level. The key differences between the Spongopylidae and the Trematodiscidae are that: (a) the pylome space is directly connected to the microsphere, (b) a porous but discrete wall surrounds the pylome, and (c) the area outside of the microsphere is structure-less, of non-hoop type so it might appear as fine bubbles in certain cases. Typical Spongopylidae have a structureless spongious disk so that Spongospira may not belong to this family. Many genera are in open nomenclature due to the difficulty of recognition about the detailed “spongy” and central structures. Many genera remain undescribed (e.g., Ogane & Suzuki 2006: pl. 1, figs 3-4).

The internal skeletal structure of Spongobrachiopyle was illustrated (Nakaseko & Nishimura 1982: pl. 39, figs 1-3; pl. 40, figs 5, 6). Illustration of living forms was documented for Spongobrachiopyle (Suzuki & Not 2015: fig. 8.10.10) and Schizodiscus (Suzuki & Not 2015: fig. 8.10.3). Protoplasm was analyzed with epi-fluorescent DAPI dyeing techniques in Schizodiscus (Zhang et al. 2018: 14, fig. 16), Spongobrachiopyle (Zhang et al. 2018: 19, fig. 10) and Spongospira (Zhang et al. 2018: 13, fig. 19). Following epi-fluorescent DAPI dyeing analyses, the protoplasm of aforementioned genera are defined below.

VALIDITY OF GENERA

Schizodiscus

The endoplasm is white in the center, opaque red in major thinner disk parts, with white zones in the thicker peripheral disk parts and reddish granule zones on the periphery of the disk. The DAPI autofluorescent red endoplasm is distributed in a U-letter shape. Most of these peripherical parts overlap in the disk’s thin opaque red zone. This difference is marked in this genus.

Spongobrachiopyle

The dark grey endoplasm fills the inner shell. The protoplasm emits an autofluorescent-whitish light blue with DAPI in the spongy shell and does not include the peripheral area beneath the gown. A thick, strong axoflagellum is affixed to the walled pylome and extends outward. Pseudopodia radiate throughout the shell. This difference is marked in this genus.

Spongospira

The protoplasm fills the center, the area around the pylome from the center to the periphery, and the thick peripheral area. This difference is marked in this genus.