Laxifenestella placida Moore, 1929

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 : 21

Laxifenestella placida Moore, 1929

Figures 10H , 11 A-D; Appendix

1929 Laxifenestella placida Moore , p. 17, pl.

2, figs. 5-7.

Material. SNSB-BSPG 2020 XCI 35, SNSB-BSPG 2020 XCI 65, SNSB-BSPG 2020 XCI 67, SNSB-BSPG 2020 XCI 108.

Exterior description. Reticulate colonies formed by straight branches joined by relatively narrow flat dissepiments. Fenestrules oval to rectangular. Autozooecia arranged in two rows on branches. Autozooecial apertures circular, with low peristome; four to five apertures spaced per fenestrule length. Rounded nodes on the low keel, widely spaced. Reverse side finely striated.

Interior description. Autozooecia relatively long, roughly pentagonal to rectangular in mid-tangential section; with short to moderately long vestibule in longitudinal section. Axial wall between autozooecial rows straight to weakly undulating; aperture positioned at distal end of chamber. Both superior and inferior hemisepta long. External laminated skeleton well-developed on both obverse and reverse sides traversed by abundant microstylets. Microstylets 0.005 –0.008 mm in diameter. Heterozooecia not observed.

Remarks. Laxifenestella placida Moore, 1929 , differs from L. stuckenbergi ( Nikiforova, 1938) from the Upper Carboniferous – Lower Permian of Russia in having wider branches (branch width 0.32– 0.54 mm vs. 0.23–0.28 mm in L. stuckenbergi ), and in larger fenestrules (fenestrule width 0.30– 0.53 mm vs. 0.15–0.22 in L. stuckenbergi ; fenestrule length 0.82–1.35 mm vs. 0.35–0.45 mm in L. stuckenbergi ). Laxifenestella placida Moore, 1929 , differs from L. benskiensis ( Schulga-Nesterenko, 1951, from the Mississippian (Serpukhovian) of Russia in having wider branches (0.32–0.54 mm vs. 0.30–0.35 mm in L. benskiensis ), and in larger fenestrules (fenestrule width 0.30–0.53 mm vs. 0.30–0.45 in L. benskiensis ; fenestrule length 0.82–1.35 mm vs. 0.70–0.80 mm in L. benskiensis ).

Occurrence. Upper Graham Formation, Pennsylvanian (Virgilian); Texas, 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).

FIGURE 11. Laxifenestella placida Moore, 1929 (A–D): A – tangential section showing autozooecial apertures and keel with nodes (XCI 35); B – deep tangential section showing autozooecial chambers with hemisepta (XCI 65); C, D – colony fragment showing fenestrules, autozooecial apertures and keels with nodes (XCI 108). Laxifenestella texana n. sp. (E, F) – tangential section showing fenestrules, autozooecial apertures and chambers, keels with nodes, and reproductive heterozooecia (arrows), holotype (XCI 81).