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Nematosphaeropsis silsila
Nematosphaeropsis silsila Guédé and Slimani in Guédé et al., 2014, p.295–298, figs.3A–L,4A–B.
Holotype: Guédé et al., 2014, figs.3A–C.
Age: late Maastrichtian.
Original description (Guédé et al., 2014):
Nematosphaeropsis silsila Guédé and Slimani nov. sp. Fig. 3, Fig. 4 and Fig. 5
Etymology: Named after silsila (Arabic): with reference to the chain-like pairs of penitabular trabeculae
Holotype: Sample Th4, slide 1, EF coordinates Y34 (Fig. 3(A–C)). Specimen dimensions: total length 60 μm, total width 58 μm, central body length 45 μm, central body width 43 μm.
Paratype: Sample Th5, slide 1, EF coordinates F36 (Fig. 3(D, E)). Specimen dimensions: total length 57 μm, total width 53 μm, central body length 47 μm, central body width 45 μm.
Repository: Botanical collection of the National Herbarium (RAB), Scientific Institute, Mohammed V-Agdal University, Rabat, Morocco.
Type locality and horizon: Tahar section (Jbel Tahar, Arba Ayacha, Larache Province, northwestern Morocco), Upper Maastrichtian; sample Th4, ca. 64 m below the K–Pg boundary.
Occurrence: Upper Maastrichtian (samples Th1 to Th7b, Tahar section; this study).
Measurements (min-[mean]-max; 20 specimens measured): total length 54-[58]-80 μm, total width 40-[55]-69 μm, central body length 42-[52]-68 μm, central body width 26-[36]-47 μm, processes length 5–10 μm
Diagnosis: A species of Nematosphaeropsis characterized by a smooth central body wall and numerous sutural (gonal and intergonal) processes which are short, slender, closely and equidistantly spaced, aligned and joined distally by chain-like pairs of thin membranous penitabular trabeculae. The paratabulation is clearly expressed by a precingular archeopyle type P and rows of parasutural processes on the central body, and by the trabecular shell.
Description: This proximate to proximochorate dinoflagellate cyst is of intermediate size and has a spheroidal, ovoidal to rhomboidal central body. The hypocyst is more broadly rounded than the epicyst. The central body wall consists of a smooth, hyaline and thin autophragm with a maximum thickness of 1 μm. The central body bears numerous slender, solid or hollow processes 5 to 10 μm in length. The processes are proximally and distally slightly expanded and aligned in parasutural rows; they reflect a paratabulation. The length of the processes is quasi-constant on a single specimen, but varies slightly within the species. The processes are circular in cross-section, closely and equidistantly spaced, proximally free, but connected distally by paired chain-like thin membranous penitabular trabeculae. The distal ends of the intergonal processes are finely bifurcate, whereas those of the gonal processes are trifurcate. Each process furcation gives rise to two penitabular trabeculae. The reflected gonyaulacoid paratabulation is 4′, 5′′, 6c, 5–6′′′, 1p, 1′′′′, 4–5s. The strongly laevorotatory paracingulum (max. width: 12 μm) is bordered by two parallel parasutural rows of processes. Every row ends distally with a pair of penitabular trabeculae. The parasulcus may be divided into 4 to 5 paraplates, with the anterior sulcal and posterior sulcal paraplates often clearly delineated. The apical paraplate 4′, which has a contact with the anterior sulcal paraplate (Fig. 3 and Fig. 4), and the strongly laevo-rotatore paracingulum suggest a S-type arrangement characterizing the Spiniferites complex ( Evitt, 1985). The precingular paralate 6′′ is undifferenciated and included in the sulcus, and only 5 precingular paraplates (1′′–5′′) are delimited by parasutural features. The posterior intercalary 1p, the posterior sulcal ps, and the antapical 1′′′′ paraplates show a partiform hypocystal arrangement ( Fig. 3 and Fig. 4). The postcingular paraplate 1′′′ is reduced and included in the sulcus. The postcingular paraplate 6′′′ does not have a contact with the antapical paraplate 1′′′′, and only three (3′′′, 4′′′, and 5′′′) among the postcingular paraplates, and the 1p and ps paraplates have contact with the pentagonal paraplate 1′′′′. The precingular archeopyle (type P) is formed by the loss of the paraplate 3′′. The operculum is free.
Remarks:Wrenn (1988) erected the genus Unipontidinium in order to separate species with a single parasutural trabeculum from species of Nematosphaeropsis Deflandre and Cookson, 1955, with two penitabular trabeculae connecting gonal or gonal and intergonal processes distally. The same author transferred Nematosphaeropsis aquaeductus and N. grande to Unipontidinium based on the presence of a single parasutural trabeculum. Consequently N. silsila Guédé and Slimani nov. sp. is here assigned to Nematosphaeropsis, since it bears two penitabular trabeculae connecting the gonal and intergonal processes distally.
The new species resembles Unipontidinium grande by its numerous parasutural (gonal and intergonal) processes, which are short, uniform, aligned and closely spaced, but differs distinctly by its thinner and smooth (rather than thick and densely granulate) central body wall. The processes of the new species are furthermore connected distally by chain-like pairs of thin membranous penitabular trabeculae and not by a single membranous parasutural trabeculum. Furthermore, U. grande bears parasutural crests joining proximally. Nematosphaeropsis lativittatus Wrenn, 1988 also possesses numerous processes, but these are more widely spaced, relatively longer when compared to the central body diameter, and connected distally by very broad, often fused, ribbon-like trabeculae rather than chain-like paired thin membranous trabeculae. N. silsila Guédé and Slimani nov. sp. differs from all other species of Nematosphaeropsis by its smooth central body wall and its numerous parasutural processes, which are short, slender, closely spaced and joined distally by two thin membranous penitabular trabeculae.
Holotype: Guédé et al., 2014, figs.3A–C.
Age: late Maastrichtian.
Original description (Guédé et al., 2014):
Nematosphaeropsis silsila Guédé and Slimani nov. sp. Fig. 3, Fig. 4 and Fig. 5
Etymology: Named after silsila (Arabic): with reference to the chain-like pairs of penitabular trabeculae
Holotype: Sample Th4, slide 1, EF coordinates Y34 (Fig. 3(A–C)). Specimen dimensions: total length 60 μm, total width 58 μm, central body length 45 μm, central body width 43 μm.
Paratype: Sample Th5, slide 1, EF coordinates F36 (Fig. 3(D, E)). Specimen dimensions: total length 57 μm, total width 53 μm, central body length 47 μm, central body width 45 μm.
Repository: Botanical collection of the National Herbarium (RAB), Scientific Institute, Mohammed V-Agdal University, Rabat, Morocco.
Type locality and horizon: Tahar section (Jbel Tahar, Arba Ayacha, Larache Province, northwestern Morocco), Upper Maastrichtian; sample Th4, ca. 64 m below the K–Pg boundary.
Occurrence: Upper Maastrichtian (samples Th1 to Th7b, Tahar section; this study).
Measurements (min-[mean]-max; 20 specimens measured): total length 54-[58]-80 μm, total width 40-[55]-69 μm, central body length 42-[52]-68 μm, central body width 26-[36]-47 μm, processes length 5–10 μm
Diagnosis: A species of Nematosphaeropsis characterized by a smooth central body wall and numerous sutural (gonal and intergonal) processes which are short, slender, closely and equidistantly spaced, aligned and joined distally by chain-like pairs of thin membranous penitabular trabeculae. The paratabulation is clearly expressed by a precingular archeopyle type P and rows of parasutural processes on the central body, and by the trabecular shell.
Description: This proximate to proximochorate dinoflagellate cyst is of intermediate size and has a spheroidal, ovoidal to rhomboidal central body. The hypocyst is more broadly rounded than the epicyst. The central body wall consists of a smooth, hyaline and thin autophragm with a maximum thickness of 1 μm. The central body bears numerous slender, solid or hollow processes 5 to 10 μm in length. The processes are proximally and distally slightly expanded and aligned in parasutural rows; they reflect a paratabulation. The length of the processes is quasi-constant on a single specimen, but varies slightly within the species. The processes are circular in cross-section, closely and equidistantly spaced, proximally free, but connected distally by paired chain-like thin membranous penitabular trabeculae. The distal ends of the intergonal processes are finely bifurcate, whereas those of the gonal processes are trifurcate. Each process furcation gives rise to two penitabular trabeculae. The reflected gonyaulacoid paratabulation is 4′, 5′′, 6c, 5–6′′′, 1p, 1′′′′, 4–5s. The strongly laevorotatory paracingulum (max. width: 12 μm) is bordered by two parallel parasutural rows of processes. Every row ends distally with a pair of penitabular trabeculae. The parasulcus may be divided into 4 to 5 paraplates, with the anterior sulcal and posterior sulcal paraplates often clearly delineated. The apical paraplate 4′, which has a contact with the anterior sulcal paraplate (Fig. 3 and Fig. 4), and the strongly laevo-rotatore paracingulum suggest a S-type arrangement characterizing the Spiniferites complex ( Evitt, 1985). The precingular paralate 6′′ is undifferenciated and included in the sulcus, and only 5 precingular paraplates (1′′–5′′) are delimited by parasutural features. The posterior intercalary 1p, the posterior sulcal ps, and the antapical 1′′′′ paraplates show a partiform hypocystal arrangement ( Fig. 3 and Fig. 4). The postcingular paraplate 1′′′ is reduced and included in the sulcus. The postcingular paraplate 6′′′ does not have a contact with the antapical paraplate 1′′′′, and only three (3′′′, 4′′′, and 5′′′) among the postcingular paraplates, and the 1p and ps paraplates have contact with the pentagonal paraplate 1′′′′. The precingular archeopyle (type P) is formed by the loss of the paraplate 3′′. The operculum is free.
Remarks:Wrenn (1988) erected the genus Unipontidinium in order to separate species with a single parasutural trabeculum from species of Nematosphaeropsis Deflandre and Cookson, 1955, with two penitabular trabeculae connecting gonal or gonal and intergonal processes distally. The same author transferred Nematosphaeropsis aquaeductus and N. grande to Unipontidinium based on the presence of a single parasutural trabeculum. Consequently N. silsila Guédé and Slimani nov. sp. is here assigned to Nematosphaeropsis, since it bears two penitabular trabeculae connecting the gonal and intergonal processes distally.
The new species resembles Unipontidinium grande by its numerous parasutural (gonal and intergonal) processes, which are short, uniform, aligned and closely spaced, but differs distinctly by its thinner and smooth (rather than thick and densely granulate) central body wall. The processes of the new species are furthermore connected distally by chain-like pairs of thin membranous penitabular trabeculae and not by a single membranous parasutural trabeculum. Furthermore, U. grande bears parasutural crests joining proximally. Nematosphaeropsis lativittatus Wrenn, 1988 also possesses numerous processes, but these are more widely spaced, relatively longer when compared to the central body diameter, and connected distally by very broad, often fused, ribbon-like trabeculae rather than chain-like paired thin membranous trabeculae. N. silsila Guédé and Slimani nov. sp. differs from all other species of Nematosphaeropsis by its smooth central body wall and its numerous parasutural processes, which are short, slender, closely spaced and joined distally by two thin membranous penitabular trabeculae.