Dictyorbitolininae Schroeder, 1990

SCHLAGINTWEIT, FELIX & RASHIDI, KOOROSH, 2021, Dictyoconella Henson, 1948, Upper Cretaceous Larger Benthic Foraminifera: A Taxonomic Revision With The Establishment Of Gusicella Gen. Nov. (Type-Species Dictyoconella Minima Henson), Acta Palaeontologica Romaniae 17 (2), pp. 3-13 : 10

Subfamily Dictyorbitolininae Schroeder, 1990 (in Schroeder et al., 1990)

Remarks: Subfamily Dictyorbitolininae includes the following genera: Dictyorbitolina Cherchi & Schroeder, 1976 , Praedictyorbitolina Schroeder in Schroeder et al., 1990, Paracoskinolina Moullade, 1965 (see Schroeder in Schroeder et al., 1990) of the Lower Cretaceous, Gusicella gen. nov. of the Upper Cretaceous, and Schroedericonus Schlagintweit, 2020b of the Paleogene.

Genus Gusicella n. gen.

Type species: Dictyoconella minima Henson, 1948 . Holotype P. 35838 in Henson (1948), stored at the Natural History Museum London (see also https://data.nhm.ac.uk).

Derivation of the name: The name is dedicated to Ivan Gusič for his numerous contributions to Mesozoic benthic foraminifera and dasycladalean algae.

Diagnosis: Finely agglutinated shell of medium conical morphology; wall thin, without any texture. Early stage with small embryo and an eccentric spire consisting of a few compressed chambers (~ half a whorl) displaying an angular margin in vertical section. Transverse section of the cone can be slightly compressed. Adult conical part with numerous rectilinear chambers subdivided into marginal and central zones separated by an undivided marginal trough. Marginal zone with several orders of beams and rafters forming a polygonal network. Main vertical partitions (beams) continuous between chambers. Central zone with pillars alternating between successive chambers; secondary deposits may be present. Marginal foramina are inclined at about 45 degrees with respect to the cone axis and form a circular row at the outer margin of the marginal trough. Multiple foramina situated in the central test part. Microspheric forms presumably broader and with convex cone base.

Comparisons: Due to the vertically alignment of the main partitions, Gusicella belongs to the Dictyorbitolininae as defined by Schroeder in Schroeder et al. (1990). Gusicella is so far the only genus of the Dictyorbitolininae reported from the Late Cretaceous Global Community Maturation Cycle of larger benthic foraminifera (e.g., Hottinger, 1997, Consorti, 2017). Dictyoconella Henson instead with its alternating vertical skeletal elements belongs to the Dictyoconinae Moullade (see discussion in Schlagintweit et al., 2016). The discreteness of Gusicella gen. nov. is given by the combined features of the initial part, and structural (exo- and endoskeleton) and foraminal features. Dictyorbitolina Cherchi and Schroeder has an apical embryo consisting of a simple protoconch and septulate deuteroconch, and alternating pillars in the central zone. It is worth noting that Dictyorbitolina was previously placed within the subfamily Orbitolininae ( Cherchi and Schroeder, 1976; Loeblich and Tappan, 1987), then transferred to the Dictyorbitolininae by Schroeder in Schroeder et al. (1990). Praedictyorbitolina Schroeder et al., 1990 has a simple embryo in eccentric position and alternating pillars in the central zone. In Paracoskinolina Moullade, 1965 , the main partitions and pillars are aligned between the consecutive chambers.

Henson (1948, p. 24–25) noted the presence of a “zone with undivided chamber space” (or marginal ridge) between the marginal (with exoskeleton) and central zones (with endoskeleton; see also Hottinger, 2006, p. 22) as also described from Dictyoconus Blanckenhorn by Davies (1930: marginal trough; see Figs. 7a , 9d ). Henson (1948, p. 26) also noted that in D. minima “the interseptal structures are sporadic and poorly defined in the central shield” (= central zone). In this context, Henson (ibidem) was obviously referring to the presence of secondarily infilled shell material as for instance reported from the Pfenderinidae Smout and Sugden or the orbitolinid Carinoconus Cherchi & Schroeder ( Loeblich and Tappan, 1987). The characteristics compared to those of the dictyoconid genera Carinoconus Cherchi & Schroeder and Dictyoconus Blanckenhorn are compiled in figure 6.

Remarks: The new compilation shows that the post- Cenomanian Upper Cretaceous Orbitolinidae consists of nine genera which in alphabetical order are: Abrardia Neumann & Damotte , Calveziconus Caus & Cornella , Dictyoconella Henson , Dictyoconus Blanckenhorn , Falsurgonina Arnaud-Vanneau , Gusicella Schlagintweit & Rashidi , Orbitolinopsis Henson , Paleodictyoconus Moullade , and Pseudorbitolina Douvillé.

Figures

Fig. 7 Gusicella minima (Henson) gen. et comb. nov. from the late Maastrichtian of the Tarbur Formation, SW Iran (Mandegan section: b, l; Naghan section: a, c–k). a Oblique transverse section. b Oblique section cutting the marginal (upper part) and central zones (lower part) displaying irregularly distributed fused pillars/secondary deposits. c, k Subaxial sections. d–g, Axial sections showing initial spire. h–i Details (from e and g) of the initial spire. j Tangential section. Slightly oblique transverse sections showing subdivision of the marginal zone and circle of marginal apertures (left and above). Abbreviations: m.f. = marginal foramen, m.t. = marginal trough, pr = protoconch, s.d. = secondary deposits/fused pillars. Thin sections: 2Ng 17 (a, k), Rt 100 (b), Ng 180-1 (c), 2Ng 179-1 (d), 2Ng 168 (e, h), 2Ng 175 (f), 2Ng 174 (g, i), 2Ng 177 (j), Rt 113 (l).

Fig. 9 Gusicella minima (Henson) gen. et comb. nov. from the late Maastrichtian of the Tarbur Formation, SW Iran (Naghan section: c–f, h–k); Mandegan section: a–b, g, l). a subaxial section of an assumed microspheric specimen. b–c axial sections showing initial spire with acute margin beneath the apex. d oblique section showing the marginal trough between the marginal and central zones as well as a circular row of marginal apertures between. e tangential section showing subepidermal network; septa in the lower part marked by white dash lines. f subaxial section of a possibly microspheric specimen. g transverse section. h subaxial section. i tangential section showing aligned main beams. j subaxial section of a possibly microspheric specimen. k tangential section. l slightly oblique transverse section showing several orders of vertical partitions (beams, intercalary beams), marginal trough, and pillared central zone. Abbreviations: m.f. = marginal foramen, m.t. = marginal through, pi = pillar. Thin sections: Rt 105 (a), 2Ng 17 (c), Rt 96 (b), 2Ng 167 (d), 2Ng 174 (e), 2Ng 118-1 (f), Rt 108-2b (g), 2Ng 169 (h), 2Ng 191 (i), 2Ng 176 (j), 2Ng 146 (k), Rt 111-1 (l).