Laxifenestella texana, Ernst & Claussen & Seuss & Wyse Jackson, 2022

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 texana n. sp.

Figures 11 E-F, 12A-G; Appendix

zoobank.org/ A7A6097D-A051-4B20-A58B-8FA7576AB66B

Etymology. The species is named after Texas where it was found for the first time.

Holotype. SNSB-BSPG 2020 XCI 81.

Paratypes. SNSB-BSPG 2020 XCI 109, SNSB-BSPG 2020 XCI 110, SNSB-BSPG 2020 XCI 111.

Type locality. TXV-200 (“Spillway section at Lost Creek Lake”), Texas, USA.

Type stratum. Graham Formation, Pennsylvanian (Virgilian).

Diagnosis. Laxifenestella species with straight branches joined by relatively narrow dissepiments, oval to rectangular fenestrules, three to four circular apertures per fenestrule length and single node in peristome, directed into the next fenestrule; densely spaced rounded nodes on the low keel; reverse side finely striated; long superior and inferior hemisepta; apparent reproductive abundant heterozooecia in form of isolated zooecia with enlarged endozonal chambers.

Exterior description. Reticulate colonies formed by straight branches joined by relatively narrow dissepiments. Fenestrules oval to rectangular. Autozooecia arranged in two rows on branches. Autozooecial apertures circular, with low peristome; three to four apertures spaced per fenestrule length. Single node in peristome, directed into the next fenestrule ( Figure 12G ). Rounded nodes on the low keel, closely 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 microstylets. Microstylets 0.003 –0.005 mm in diameter. Apparent reproductive heterozooecia in form of isolated zooecia with enlarged endozonal chambers abundant ( Figure 12 B-C, E-F). Chambers rounded to oval, 0.11– 0.16 mm in diameter. Nanozooecia present ( Figure 12G ).

Remarks. Laxifenestella texana n. sp. differs from L. placida Moore, 1929 , in possessing narrower branches (branch width 0.23–0.34 mm vs. 0.32– 0.54 mm in L. placida ), and in smaller fenestrules (fenestrule width 0.20–0.33 mm vs. 0.30–0.53 in L. placida ; fenestrule length 0.44–0.70 mm vs. 0.82– 1.35 mm in L. placida ). Laxifenestella texana n. sp. differs from L. stuckenbergi ( Nikiforova, 1938) from the Upper Carboniferous – Lower Permian of Russia in having larger fenestrules (fenestrule width 0.20–0.33 mm vs. 0.15–0.22 in L. stuckenbergi ; fenestrule length 0.44–0.70 mm vs. 0.35–0.45 mm in L. stuckenbergi ). Furthermore, Laxifenestella texana n. sp. has smaller and closer nodes on the obverse keel.

Figures

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).

FIGURE 12. Laxifenestella texana n. sp. (A–G): A–C – tangential section showing autozooecial apertures and chambers, and reproductive heterozooecia (arrows) (holotype XCI 81). D – colony fragment showing fenestrules, autozooecial apertures divided by keels with nodes (paratype XCI 109); E – colony fragment showing reproductive heterozooecia (arrows) (paratype XCI 109); F – almost intact chamber of a reproductive heterozooecium (paratype XCI 110); G – colony fragment showing secondary nanozooecia (arrows) (paratype XCI 111). Cavernella praecavifera (Schulga-Nesterenko, 1951) (H) – colony fragment showing fenestrules, autozooecial apertures divided by keels with nodes (XCI 112).