Fabifenestella compactilis ( Condra, 1902 )

Ernst, Andrej, Claussen, Anna Lene, Seuss, Barbara & Wyse Jackson, Patrick N., 2022, Stenolaemate bryozoans from the Graham Formation, Pennsylvanian (Virgilian) at Lost Creek Lake, Texas, USA, Palaeontologia Electronica (a 15) 25 (2), pp. 1-56 : 20

Fabifenestella compactilis ( Condra, 1902)

Figure 10 B-G; Appendix

1902 Fenestella conradi var. compactilis Condra , p. 348, pl. 22, figs. 1-2.

1903a Fenestella conradi-compactilis Condra, 1902 ; p. 60-61, pl. 8, figs. 11-12.

non 1941 Fenestella conradi compactilis Condra, 1902 ; Schulga-Nesterenko, p. 98-99, pl. 17, fig. 3, pl. 18, figs. 2-3.

1957 Fenestella compactilis Condra, 1902 ; Elias and Condra, p. 93-94

1957 Fenestella compactilis var. plattsmouthensis ; Elias and Condra, p. 95-96, pl.

12, figs. 6-7.

Material. SNSB-BSPG 2020 XCI 49, SNSB-BSPG 2020 XCI 62, SNSB-BSPG 2020 XCI 75, SNSB-BSPG 2020 XCI 107.

Exterior description. Reticulate colonies formed by straight branches joined by relatively wide dissepiments. Fenestrules oval to rectangular, about twice as long as wide. Autozooecia arranged in two rows on branches. Additional autozooecium often developed in the place of branch diversion. Autozooecial apertures circular, with low peristome, containing eight nodes (stellate structure); two to three apertures spaced per fenestrule length. Proximal pore present, positioned proximally to the autozooecial aperture, 0.025 –0.037 mm in diameter. Keel wide, low, containing densely spaced alternating nodes. Nodes varying in size, elliptically shaped.

Interior description. Autozooecia relatively long, roughly pentagonal to rectangular in deep tangential section, becoming fabiform in mid-tangential section; with short to moderately long vestibule in longitudinal section. Axial wall between autozooecial rows weakly to strongly undulating; aperture positioned at distal end of chamber. Hemisepta present, positioned in the distal half of autozooecial chamber. External laminated skeleton well-developed on both obverse and reverse sides. Heterozooecia not observed.

Remarks. Fabifenestella compactilis ( Condra, 1902) differs from F. praevirgosa ( Schulga-Nesterenko, 1951) from the Pennsylvanian (Gzhelian) of the Russian Platform in possessing smaller fenestrules (fenestrule width 0.15–0.27 mm vs. 0.28–0.35 mm in F. praevirgosa ; fenestrule length 0.38–0.63 mm vs. 0.75–0.90 mm in F. praevirgosa ). Fabifenestella compactilis differs from F. almazani Ernst and Vachard, 2017 , from the Pennsylvanian (Moscovian) of Mexico in the closer spacing of fenestrules (average distance between dissepiment centres 0.67 mm vs. 0.74 mm in F. almazani ), and in wider spacing of autozooecial apertures (average distance between aperture centres along branches 0.28 mm vs. 0.23 mm in F. almazani ).

Morozova (2001) listed the species Minilya conradi-compactilis ( Condra, 1902). However, the placement of this species in the genus Minilya Crockford, 1944, appears incorrect. The original description, as well as the following ones, was performed without use of thin sections, therefore, the generic assignment could not be clarified with certainty. However, Elias and Condra (1957, p. 94) described the shape of the autozooecia as follows: “Outline of zooecial chamber subpentagonal at base, but transverse sides of pentagons strongly inclined distad; at slightly higher level central zigzag line becomes nearly straight, pentagons inclined forwardly become parallelograms, …”. They also depicted images of polished slabs showing the internal shape of autozooecia on the pl. 12, fig. 5 (Fenestella compactilis) and fig. 7 (Fenestella compactilis var. plattsmouthensis). The shape of the autozooecia in both species is identical and typically fabiform, not triangular or trapezoid as in Minilya.

Occurrence. Cass Limestone, Douglas Group, Pennsylvanian (Virgilian); Nebraska, USA. Graham Formation, Pennsylvanian (Virgilian); TXV-200 (“Spillway section at Lost Creek Lake”), Texas, USA.

Figures

FIGURE 10. Chainodictyon minor Ulrich, 1890, (A): longitudinal thin section showing autozooecial chambers (XCI 42). Fabifenestella compactilis (Condra, 1902) (B–G): B – tangential section showing autozooecial apertures and chambers with hemisepta (XCI 49); C–E – fragment of colony showing fenestrules, autozooecial apertures and keels with nodes (arrow – apertural pore) (XCI 107); F, G – tangential section showing autozooecial apertures and chambers with hemisepta, and keels with nodes (XCI 62). Laxifenestella placida Moore, 1929 (H) – deep tangential section showing autozooecial chambers with hemisepta (XCI 65).