Brightonicystis gregaria Paul, 1971

Brightonicystis gregaria Paul, 1971

Figs. 2A 2 View Fig , 6–8 View Fig View Fig View Fig .

1966 Trematocystis sp. ; Ingham 1966: 502.

1967 “ Trematocystis ” sp. nov.; Paul 1967: 147.

1967 Trematocystis sp. nov.; Jefferies et al. 1967: 569.

1971 Brightonicystis gregarius sp. nov.; Paul 1971: 143, figs. 62–64.

1972 Brightonicystis gregarius Paul ; Paul 1972: 26, pl. 7: 6.

1973 Brightonicystis gregaria Paul ; Paul 1973: 56, text-figs. 8D, 34, pl. 8: 4–9, pl. 9: 1.

1983 Brightonicystis gregarius Paul ; Frest 1983: 483, fig. 56A.

2011 Brightonicystis gregarius Paul ; Frest et al. 2012: 44, 47, 48, textfig. 29A.

2017 Brightonicystis gregaria Paul ; Paul 2017: 587, fig. 5.4.

Type material: Holotype: CAMSM A.32813, the most complete theca,

preserved in original calcite showing the humatipores; ambulacrum C obscured by the base of another epifaunal specimen, but otherwise showing the critical oral area. Paratypes: CAMSM A.32811 ( Fig. 6C View Fig ), an almost complete theca free of matrix but with the base of another diploporite attached ; CAMSM A.32812 ( Fig. 6B View Fig ), another almost complete theca still partially buried in sediment and with some of the plates in the oral area missing; CAMSM A.32814a, b, part and counterpart of a small area of articulated plates showing the humatopores well. All from the type locality.

Type locality: Banks of Swindale Beck, just upstream of the junction with Great Rundale Beck, near Knock, Cumbria, England, UK (National Grid reference NY688274).

Type horizon: Ashgill Shales, Hirnantian, Upper Ordovician.

Material.— Eight complete or partial thecae, including the holotype, two paratypes, and HM E5880, E5881, E5882, CAMSM A.43229, A.74804, plus numerous isolated plates, including the third paratype, CAMSM A.32814a. For details see Paul (1973: 56) .

Emended diagnosis.—A species of Brightonicystis with at least ten oral plates, a globular theca, two generations of tumid plates with smooth external surfaces; up to nine or ten tangential canals per humatipore (emended from Paul 1971: 143).

Description.—Moderate-sized theca (20–35 mm across), globular or oviform, composed of about 100–150 smooth, gently convex thecal plates with slightly impressed sutures, with pentagonal mouth opposite a relatively large attachment area. Thecal plates of two generations ( Fig. 6A View Fig 3 View Fig , B), larger primaries arranged in crude circlets, smaller secondaries usually triangular. All plates bear buried humatipores with many tangential canals ( Fig. 6A View Fig 3 View Fig , B). Peristome pentagonal ( Figs. 6C View Fig 1 View Fig , 7A View Fig 1 View Fig , A 2 View Fig ) about 8 mm wide externally surrounding an oval mouth 6 mm wide in the holotype which is slightly crushed in an anterior-posterior direction; with a border up to 1.5 mm wide and with many oral pores ( Fig. 6A View Fig 1 View Fig ). Peristome frame composed of nine plates arranged as in Fig. 7A View Fig 2 View Fig . Narrow food grooves pass from the five ambulacral facets across the peristome border ( Fig. 7 View Fig : ambulacra B, D, and E; Fig. 8 View Fig : ambulacra D, E, and A). Facets are oval, 2×1.7 mm, with a central ridge separating two lateral depressions, and developed on plates of both the oral and facetal

A 3

circlets ( Figs. 6A View Fig 1 View Fig , 7A View Fig 2 View Fig , 8A View Fig 3 View Fig ), one facet per ambulacrum, except that paratype CAMSM A.32812 has two in the D ambulacrum ( Fig. 8 View Fig ). Feeding appendages unknown. The periproct is polygonal, surrounding a rounded anus about 4 mm across ( Figs. 6A View Fig 3 View Fig , 8A View Fig 3 View Fig ). Oral and anal cover plates are unknown. The gonopore is a small circular orifice, 0.4 mm across, in the plate immediately adoral to the periproct and very close to the periproct border ( Figs. 6A View Fig 3 View Fig , 7A View Fig 2 View Fig ). A hydropore has not definitely been detected, although there is a groove in O1 of the holotype ( Fig. 7A View Fig 2 View Fig ). Attachment was direct by a large smooth attachment area up to about 50% of the thecal diameter. The holotype ( CAMSM A.32813) and paratype ( CAMSM A.32811a) both bear the bases of additional examples that attached post mortem ( Fig. 6A View Fig 3 View Fig , C 2 View Fig ) .

Remarks.— Brightonicystis gregaria is characterized by a relatively modest globular theca, with smooth gently convex plates of two generations and humatipores with numerous tangential canals. The mouth is surrounded by at least ten oral plates, two of which in the B and D ambulacra do not reach the inner margin of the peristome. These characteristics are only shared by Holocystites salmoensis Sheffield et al., 2018, with which Brightonicystis gregaria is compared. For further discussion see after the description of Brightonicystis salmoensis .

Stratigraphic and geographic range.— Brightonicystis gregaria comes from the Ashgill Shales (Hirnantian) from several lower Palaeozoic inliers in Cumbria and West Yorkshire, northern England, UK.

Brightonicystis salmoensis ( Sheffield et al., 2018) comb. nov.

Figs. 3 View Fig , 9 View Fig .

2018 Holocystites salmoensis sp. nov.; Sheffield et al. 2018: 4, fig. 5.

2022 “ Holocystites ” salmoensis Sheffield, Ausich, and Sumrall; Paul 2022: 470, fig. 1.

Holotype: GSC 126899 View Materials , an incomplete, weathered theca preserved in original calcite showing the humatipores and oral plating.

Type locality: Road cut along the Salmon-Table Head Road, 800 m east of Macaire Creek , Salmon River Valley , Anticosti Island , Canada. Type horizon: Ellis Bay Formation , Laframboise Member , Hirnantian, Upper Ordovician .

Material.— Twelve complete or partial thecae, including holotype GSC 126899 View Materials and paratypes GSC 126896 View Materials , 126897 View Materials , 126898 View Materials , 126900 View Materials , 126902 View Materials , 126903 View Materials a, 126903b, 126903c, 126906, 126907, 126908.

Emended diagnosis.—A species of Brightonicystis with nine oral plates, relatively large, globular to pyriform theca, two generations of tumid plates with smooth external surfaces; with two-four tangential canals per humatipore (simplified from Sheffield et al. 2018: 4).

Description.—Theca globular to pyriform depending on the relative size of the attachment area, composed of over 100 smooth, convex thecal plates with distinctly impressed sutures, with a pentagonal mouth. Thecal plates of two generations in paratype GSC 126906 ( Sheffield et al. 2018: fig. 5E), larger primaries arranged in oblique, apparently closed circlets of about ten plates; smaller secondaries usually pentangular inserted between primary circlets. All plates bear buried humatipores with relatively few tangential canals ( Fig. 9A View Fig 1 View Fig ).

Peristome pentagonal ( Fig. 9 View Fig ), surrounding an oval mouth. Peristome border deeply weathered in holotype and paratype GSC 126897 View Materials ( Fig. 9 View Fig ), but with a frame composed of nine plates arranged as in Fig. 9A View Fig 3 View Fig , including two in the B and D ambulacra that do not reach the inner margin of the peristome. Feeding appendages unknown .

The periproct is hexagonal, surrounding a rounded anus in GSC 126897 ( Sheffield et al. 2018: fig. 5D). Oral and anal cover plates are unknown. The gonopore is a small circular orifice in the plate immediately adoral to the periproct in GSC 126897 ( Sheffield et al. 2018: fig. 5D). A hydropore has not definitely been detected. Attachment was direct but the details of the attachment area are unknown.

Remarks.— Brightonicystis salmoensis is so similar to Brightonicystis gregaria that it is difficult to give a differential diagnosis. It appears to have more tumid thecal plates, arranged in oblique, closed circlets with a larger number of primary plates, and fewer tangential canals per humatipore, than B. gregaria . Both come from similar aged Hirnantian strata but well below the Ordovician/Silurian boundary. Both species attributed to the genus Brightonicystis are characterized by relatively small, globular thecae, composed of two generations of smooth, gently convex plates with many humatipores. The mouth is surrounded by a closed circlet of nine plates in Brightonicystis salmoensis , two of which lying in the B and D ambulacra do not reach the inner margin of the peristome. A second circlet of plates surrounds the oral circlet and five single facets for unknown feeding appendages are shared by plates of both circlets. The critical oral area is only known from a single specimen. Sheffield (2017: 18), Sheffield and Sumrall (2017: 756; 2019: 743) and Sheffield et al. (2018: 2) have expressed doubts as to the validity of the genus Brightonicystis . The oral area of Brightonicystis gregaria is partly known in three specimens. Nevertheless, the details of ambulacrum C are not seen in any of them. Food grooves in the A, B, D and E ambulacra lie along plate sutures and sutures also occur between these ambulacra. If ambulacrum C is the same, the total number of oral plates is eleven, as an additional interradial plate lies in the CD interambulacrum.

The unexpected plate arrangement in which a plate in the B and D ambulacra reaches the edge of the peristome, but not the inner margin of the mouth, can be confirmed in both ambulacra of the holotypes of both Brightonicystis salmoensis and Brightonicystis gregaria . The D ambulacrum of paratype CAMSM A.32812 of Brightonicystis gregaria shows the same arrangement ( Fig. 8 View Fig ) but plates of the B ambulacrum are missing. In contrast, the suture in the B ambulacrum of paratype CAMSM A.32811 does not appear to branch ( Fig. 6C View Fig 1 View Fig ). In addition, paratype CAMSM A.32812 has two facets in the D ambulacrum, whereas all other known holocystitids have only a single facet per ambulacrum. Thus, it seems unwise to assume the characters of the unseen facet in ambulacrum C of Brightonicystis gregaria . If all ambulacra are the same, Brightonicystis gregaria has eleven oral plates. If not, the plate arrangement in Brightonicystis gregaria was not fixed, but varied from individual to individual. What is certain, however, is that both Brightonicystis gregaria and Brightonicystis salmoensis have more oral plates and they are more similar to each other than to any other holocystitid genus. The practical solution to this dilemma is to assign them both to the genus Brightonicystis for which a rather unsatisfactory diagnosis of ‘with nine or more orals’ forms part.

The characters discussed above distinguish Brightonicystis from the only other holocystitid genus with ambulacral facets developed on oral and facetal plates, Holocystites . The latter has only six oral plates which have a variable relationship to the overlying facets and food grooves (see below).

Stratigraphic and geographic range.— Brightonicystis salmoensis is only known from the Ellis Bay Formation, Laframboise Member, Hirnantian, Upper Ordovician of NE Anticosti Island, Canada.

Genus Holocystites Hall, 1864

Type species: Caryocystites cylindricus Hall, 1861 , by subsequent designation of Miller 1889: 253, from the Racine Dolomite, Sheinwoodian lower Silurian), Grafton, Wisconsin, USA.

Species included: Type species and Holocystites abnormis Hall, 1864 , Holocystites alternatus ( Hall, 1861) , Holocystites clavus Frest & Strimple in Frest et al., 2011, Holocystites greenevillensis Foerste, 1917 , Holocystites ovatus Hall, 1864 , Holocystites scutellatus Hall, 1864 , Holocystites spangleri Miller, 1891 .

Emended diagnosis.—Holocystitids with cylindrical, globular or pyriform thecae, five ambulacral facets shared by oral and facetal plates, six irregular orals with food grooves crossing them, humatipores typically tubercular, but buried beneath smooth plates in at least one species (simplified from Paul 1971: 73).

Remarks.—In Holocystites ( Figs. 1A View Fig , 10 View Fig , 11 View Fig ) the theca may be cylindrical, oval or pyriform, often with a small aboral extension. The attachment area is usually small. Thecal plates may be of one to three generations, with primary plates usually in closed circlets of eight plates. In Holocystites alternatus ( Hall, 1861) there are circlets of primary, secondary and tertiary plates that alternate regularly in the order primary, tertiary, secondary, tertiary, primary ( Fig. 11A View Fig ). In contrast, Holocystites cylindricus is entirely composed of primary plates ( Fig. 11B View Fig ). The plates usually have tubercular humatipores ( Fig. 10A View Fig 1 View Fig ), but in Holocystites abnormis Hall, 1864 , the thecal surface is smooth with buried humatipores. The mouth is surrounded by six oral plates with five concave facets shared by oral and facetal plates ( Fig. 10 View Fig ). Food grooves are more often on the oral plates than along the sutures between them, in contrast to all other holocystitid genera in which the food grooves follow oral sutures. Only in the C radius do food grooves cross or lie close to the oral suture. The peristome border is pitted with oral pores and covered by a palate of six cover plates in Holocystites scutellatus Hall, 1864 ( CMCIP 75376, Hill 2022: fig. 1.7: 2). Two palatals are preserved in a specimen of Holocystites cylindricus ( FMNH 10695, Paul 1971: fig. 25). The oral circlet is surrounded by a facetal circlet of eight plates ( Fig. 10A View Fig 2 View Fig , A 3 View Fig ). The periproct is polygonal, surrounding a relatively large anus, separated from the peristome by three plates (O1, ambulacral facets developed exclusively on plates of the facetal circlet and all except Pentacystis and Moyacystis cooperi have food grooves along sutures between orals (see below).

Stratigraphic and geographic range.— Sheinwoodian–Homerian ( lower Silurian ), Midwest USA (Wisconsin, Illinois, Indiana, Ohio, Kentucky, Tennessee) .

Genus Pentacystis Paul, 1971

Type species: Pentacystis simplex Paul, 1971 , by original designation, from the Lewisburg and Massie formations, Sheinwoodian (lower Silurian), SE Indiana, USA.

Species included: Type species and Pentacystis gibsoni Frest & Strimple in Frest et al., 2011, Pentacystis sphaeroidalis ( Miller, 1891) .

Emended diagnosis.—Holocystitids with oral frame composed of eight facetal plates, orals absent (simplified from Paul 1971: 102).

O6, F1, Fig. 10A View Fig 2 View Fig , A 3 View Fig ). In life, it was covered by a simple anal pyramid, preserved in Holocystites scutellatus ( CMCIP 75377, Hill 2022: fig. 1.7: 3). The hydropore is usually a short slit, within an oval tubercle across the O1:O6 suture. The gonopore is a circular pore also set in a tubercle usually in plate F1 or rarely F2.

Among holocystitid genera only Brightonicystis and Holocystites have their ambulacral facets developed over multiple plates of the oral and facetal circlets. Holocystites differs from Brightonicystis in having an oral frame composed of six plates which are irregularly arranged with respect to the food grooves and ambulacral facets ( Fig. 10 View Fig ). The key characters of Holocystites are the presence of six oral plates, surrounded by a closed circlet of eight facetal plates and five ambulacral facets shared between orals and facetals but with a variable relationship to the underlying thecal plates. Food grooves cross individual orals. Brightonicystis also has five ambulacral facets developed on both oral and facetal plates, but has a larger number of oral plates and food grooves that usually follow oral sutures. So far, all species of Hirnantian holocystitids (which are currently attributed to Brightonicystis ) have buried humatipores beneath smooth thecal plates, whereas Holocystites may have tubercular or buried humatipores ( Paul 1971: 73; Frest 1983: 325; Frest et al. 2011: 32 and later). All other genera of holocystitids have Remarks.—In Pentacystis ( Figs. 1B View Fig , 12B View Fig ) the theca is inverted pyriform or clavate with a relatively large attachment area (Frest and Strimple in Frest et al. 2011: 19, fig. 13). Thecal plates are smooth and humatipores buried with as few as two tangential canals. The mouth is rounded and lacks the oral circlet ( Fig. 12B View Fig ). The five ambulacral facets are entirely on individual facetal plates. As there are eight facetals, the facet-bearing plates are grouped in an anterior triplet in contact (ambulacra E, A, and B), separated by plates F2 and F6 from the posterior pair of facets (ambulacra C and D), which in turn are separated from each other by plate F1 ( Fig. 12B View Fig ). Food grooves from the facets pass across the peristome border to the inner edge of the mouth ( Fig. 12B View Fig ). The theca has a relatively large attachment area.

Paul (1971: 102) attributed three species to Pentacystis , the type species of which, Pentacystis simplex Paul, 1971 , entirely lacks orals. Frest and Strimple ( Frest et al. 2011) described three new species of pentacystines and distinguished those with any orals as the genus Osgoodicystis . The type species of Osgoodicystis , Osgoodicystis bissetti has all six orals, but Osgoodicystis cooperi has only the two posterior orals present. It also differs in having oral pores developed in the facetal plates that contribute to the peristome border. To me these are generic characters and so I distinguish Osgoodicystis cooperi as type species of the new genus Moyacystis (see below). Frest (1983: 419) and Frest and Strimple ( Frest et al. 2011: 88) clearly considered the same action.

Stratigraphic and geographic range.—Sheinwoodian (lower Silurian), Indiana, USA. Pentacystis ranges from the lower limestone of the Lewisburg Formation into the base of the Massie Formation ( Frest et al. 2011: 14, fig. 10; Brett et al. 2012).