Moyacystis, Paul, 2025

Genus Moyacystis nov.

ZooBank LSID: urn:lsid:zoobank.org:act:2091DCE0-0B58-47FD-8823-5E02DF990FFE .

Etymology: Named for my wife Moya and the standard ending cystis. Type species: Osgoodicystis cooperi Frest & Strimple in Frest et al., 2011, monotypic; Lewisburg Formation, Sheinwoodian (lower Silurian), Ripley County, Indiana, USA.

Species included: Type species only.

Diagnosis.— Holocystitids with only the two posterior orals (O1 and O6), with oral pores in facetals that contribute to the peristome margin.

Remarks.— Moyacystis gen. nov. ( Figs. 12C View Fig , 15 View Fig ) has a large more or less cylindrical theca, composed of granular plates of a single generation arranged in seven or more circlets of 10–14 plates each. The mouth frame is composed of the two posterior orals (O1 and O6) plus at least parts of all the facetals except F1 ( Fig. 15A View Fig 3 View Fig ). Oral pores are present all around the peristome border ( Fig. 15A View Fig 1 View Fig ). Humatipores are rounded with few (2–3) tangential canals. The gonopore is in a low tubercle in F2. Hydropore and attachment area unknown.

Moyacystis gen. nov., Osgoodicystis Frest & Strimple in Frest et al., 2011, and Pentacysti s Paul, 1971, are all very similar, differing only in the presence of some or all the oral plates. Moyacystis cooperi has a more or less cylindrical theca, but otherwise even the thecal shapes of species in all three genera are similar. Sheffield and Sumrall (2015: 161, fig. 1B, C; 2017: 758, fig. 3) have argued that the variable number of oral plates seen in the three pentacystine genera is purely taphonomic. They considered that well-preserved examples have all the orals, as in Osgoodicystis wykoffi ( Miller, 1891) and Osgoodicystis bissetti Frest & Strimple in Frest et al., 2011, whereas more disarticulated examples have only two orals, as in Moyacystis cooperi (Frest & Strimple in Frest et al., 2011), or none at all, as in Pentacystis sphaeroidalis ( Miller & Gurley, 1895) , Pentacystis simplex Paul, 1971 , and Pentacystis gibsoni Frest & Strimple in Frest et al., 2011. The diagram to support this idea ( Sheffield and Sumrall 2015: fig. 1b, c) implies a complex and unlikely taphonomic history. The orals had to remain in place while the theca filled completely with sediment. Then they detached and moved across the mouth to accumulate on one side on top of the sediment fill.

This is not the only point against their interpretation. To illustrate their interpretation, Sheffield and Sumrall 2017: fig. 6.5) figured Osgoodicystis bissetti , with all six orals preserved and Pentacystis gibsoni , without any orals their fig. 6.3). The orals of Osgoodicystis bissetti ( Sheffield and Sumrall 2017: fig. 6.5) include the inner margin of the mouth, the peristome border (which in plate O2 clearly bears oral pores; Fig. 13A View Fig 1 View Fig ), food grooves running along the sutures between the oral plates (clearly seen in ambulacrum C; Fig. 14A View Fig 1 View Fig ), and the outer peristome border with a recess for the insertion of the cover plates ( Figs. 12A View Fig , 14A View Fig 3 View Fig ). Under Sheffield and Sumrall’s (2015) hypothesis, all these features should be missing in Pentacystis gibsoni because they are all developed on the (missing) orals. The oral opening would appear as an angular, roughly hexagonal hole defined by the outline of the oral plate circlet ( Fig. 16 View Fig ).

Sheffield and Sumrall (2017: 764) argued that the orals of Pentacystis gibsoni detached prior to burial, as the oral cover plates undoubtedly have. Their photograph of Pentacystis gibsoni ( Sheffield and Sumrall 2017: fig. 6.3) shows parts of the rounded inner margin of the mouth, a clear peristome border across which food grooves pass from the adoral edge of the facets to the inner margin of the mouth, and an outer peristome border with a recess for the insertion of cover plates ( Fig. 12B View Fig ). In short, all the features that should be missing except the oral pores in the peristome border. Frest et al. (2011: pl. 14: 1) show the oral area of Moyacystis cooperi (Frest & Strimple in Frest et al., 2011) which has oral pores in the peristome border formed by the facetal plates ( Fig. 12C View Fig ). Thus, in different pentacystine species with two or no oral plates, all the features that should be missing un- der Sheffield and Sumrall’s (2015) hypothesis are preserved. Altogether, I prefer to accept Frest’s (1983) interpretation of pentacystine holocystitids, reinstate Osgoodicystis and recognize the species with only two orals as a new genus, Moyacystis .

The remaining holocystitid genera have four ambulacra except for the unique type specimen of Pustulocystis pentax Paul, 1971 ( Fig. 17B View Fig ) which has five. Trematocystis , and Paulicystis have six orals, eight facetals and buried humatipores but Paulicystis has recumbent ambulacra. Pustulocystis has only six facetals and typically tubercular humatipores ( Table 1).

Stratigraphic and geographic range.—Lewisburg Formation, Sheinwoodian (lower Silurian), Ripley County, Indiana, USA.

Genus Trematocystis Jaekel, 1899

= Austrocystites Brown, 1963

Type species: Holocystites subglobosus Miller, 1889 (= Holocystites globosus Miller, 1878 ), by original designation, from the Osgood Formation, Sheinwoodian (lower Silurian), Jefferson County, Indiana, USA.

Species included: Type species and Trematocystis branagani ( Brown, 1963) , Trematocystis magniporatus Frest & Strimple in Frest et al., 2010, Trematocystis rotundus ( Miller, 1879) , Trematocystis wetherbyi ( Miller, 1878)

Emended diagnosis.—Holocystitids with six inter-radial orals and eight facetals, four ambulacral facets confined to a single facetal plate, food grooves along O:O sutures, humatipores buried beneath smooth external plate surface (after Paul 1971: 115).

Remarks.—In Trematocystis ( Figs. 1C View Fig , 4A View Fig ) the theca is inverted pyriform, with a relatively large attachment area and smooth thecal surface composed of only primary plates. The oral area is characterized by six interradial orals, surrounded by eight facetals only four of which bear ambulacral facets confined to a single facetal plate ( Figs. 1C View Fig , 4A View Fig ). Ambulacrum A of Carpenter (1884, 1891) always lacks a facet. USNM S3063a preserves the six palatal plates over the mouth and five anals over the periproct ( Fig. 4A View Fig ). A small oval hydropore is shared by O1 and O6; a small circular gonopore may occur in either F1 or F2 ( Figs. 1C View Fig , 4A View Fig ). Buried humatipores have 4–6 tangential canals. Trematocystis wetherbyi ( Miller, 1878) has a theca with five circlets of 14–16 primary plates. All other species, including the Australian one, have eight or nine plates per circlet.

Species of Trematocystis are distinguished on the position of the gonopore and details of the humatipores. Brown (1963: 388) described a new diploporite, Austrocystites branagani Brown, 1963 , on a unique internal mould from the Silurian of Yass, New South Wales. The specimen showed a single generation of relatively large plates, arranged in three circlets up to the level of the periproct ( Brown 1963: 389, fig. 2), the lower two circlets with eight plates each. All the plates bore casts of perpendicular canals of pore structures not arranged in rhombic patterns and with numerous pores in each plate. Brown correctly interpreted the specimen as a diploporite, but the internal mould lacked diagnostic characters on which to make a more precise identification. Brown thought Austrocystites was allied to the sphaeronitid diploporite Eucystis Angelin, 1878 .

More recently, Jell (2010: 35) described and illustrated a second internal mould as Eucystis branagani ( Brown, 1963) . This specimen clearly shows that the casts of the perpendicular canals are arranged in pairs ( Jell 2010: 36, fig. 6e). A latex cast of a small area of the external mould ( Jell 2010: fig. 6d) shows an entirely smooth external surface to parts of three plates in the second circlet up from the base of the theca. In typical diplopores the perpendicular canals pass right through the thecal plates and open in pits in the external surface called peripores ( Paul 1971: 19, fig. 6a; 1972: 6–7, figs. 6, 7). Jell (2010: 37) explained the absence of any trace of the peripores on the external surface around the supposed diplopores as being due to wear or weathering, but no amount of wear would eliminate the perpendicular canals of diplopores. Alternatively, if the pore structures were humatipores buried beneath smooth thecal plates, a cast of the inner surface would show paired pits (or tubercles on an internal mould), but an undamaged external surface would show no trace of pores ( Paul 1971: fig. 6b; 1972: 8, fig. 9b).

Immediately following his description of Eucystis branagani, Jell (2010: 37) described the holocystitid Trematocystis wrighti Jell, 2010 , which not only bears humatipores beneath smooth thecal plates, but also seems to have the thecal plates arranged in circlets of eight, as do many American holocystitids. The morphological similarity, plus the same locality and horizon suggest to me that Austrocystites is not a sphaeronitid, but a holocystitid and a junior synonym of Trematocystis . Thus, the correct name should be Trematocystis branagani ( Brown, 1963) . Peter Jell (personal communication 2025) agrees with this interpretation.

Stratigraphic and geographic range.—Sheinwoodian (lower Silurian), Indiana, USA; uppermost Ludfordian (upper Silurian), Yass Basin, New South Wales, Australia. Trematocystis in the USA ranges from the upper Osgood Formation into the base of the Massie Formation ( Frest et al. 2011: 14, fig. 10; Brett et al. 2012) in Indiana, and in Jefferson County, Kentucky, just across the Ohio River. It is also recorded in Australia from the Rainbow Hill Marl Member of the Rosebank Shale Formation, uppermost Ludlovian ( Jell 2010). This record is the youngest known occurrence of any holocystitid.

Genus Pustulocystis Paul, 1971

Type species: Holocystites ornatissimus Miller, 1891 , by original designation, from the Osgood Formation , Sheinwoodian (lower Silurian), Jefferson County, Indiana, USA .

Emended diagnosis.— Holocystitids with six interradial oral plates and six facetals, four or rarely five ambulacral facets confined to a single facetal plate, food grooves along O:O sutures, humatipores typically in raised tubercles (modified after Paul 1971: 131).

Species included: Type species and Pustulocystis pentax Paul, 1971 .

Remarks.— Pustulocystis ( Figs. 1D View Fig , 17 View Fig , 18 View Fig ) has a fusiform to globular theca composed of a single generation of distinctly pustular plates ( Fig. 18 View Fig ). The oval mouth is surrounded by the usual six interradial orals, with a closed circlet of six facetals beyond, four of which bear facets ( Fig. 17A View Fig ). The hydropore is in a tubercle across the O1:O6 suture and the gonopore in a rounded tubercle in variable positions usually across a suture between facetals, or facetal and oral plates and close to the D ray facet ( Fig. 17 View Fig ). The periproct is rounded. Cover plates of both mouth and anus are unknown. Attachment was direct, by a relatively small attachment area compared with Trematocystis . The most distinctive feature of Pustulocystis is the prickly appearance of the theca due to the prominent tubercular humatipores ( Fig. 18 View Fig ).

All but one specimen attributed to Pustulocystis bear only four ambulacral facets. The single exception, the holotype of Pustulocystis pentax Paul, 1971 , has five ( Fig. 17B View Fig ). With only one example it is impossible to tell whether this is an anomalous specimen or a distinct species. Paul (1971: 140) opted for the latter because its thecal shape was unknown in the more common Pustulocystis ornatissimus Miller, 1891 ) and because it came from an uncertain stratigraphic horizon at Newsom, Tennessee, over 300 km from all other known examples in Indiana. A third possible species was left under open nomenclature. It had a thecal shape closer to Pustulocystis ornatissimus , but smooth plates and apparently seven facetals; F7 is definitely absent, but the oral area is not well preserved.

Stratigraphic and geographic range.— Sheinwoodian ( lower Silurian ), SE Indiana, Jefferson County, Kentucky, and Pegram and Newsom , Tennessee, USA. In Indiana, Pustulocystis ornatissimus has only been recorded from Foerste’s (1897)

main cystoid bed” 23–37 cm below the top of the Osgood Formation as restricted by Brett et al. (2012).