Back
Sumatradinium hamulatum
Sumatradinium hamulatum De Verteuil and Norris 1996
Holotype: de Verteuil and Norris, 1996, Plate 16, figs. 2-5
Locus typicus: Fairhaven Section, Herring Bay, Anne Arundel County, Maryland.
Type locality: Upper lower Miocene Fairhaven Member of the Calvert Formation.
--------------------------------------------------
G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999
Sumatradinium hamulatum de Verteuil and Norris, 1996a. Diagnosis from de Verteuil and Norris (1996a, p.152-153), A species of Sumatradinium characterized by uniformly hamulate proximate luxuriae that do not form a complete reticulum; a cingulum clearly defined by two rows of low, hollow, conical or taeniate virgae; similar virgae aligned along select field boundaries, notably the apical intraseries boundaries and the posterior margin of the inferred third postcingular field; irregularly scattered, low, conical to evexate hollow virgae. Virgae are 0.75-2 µm in diameter and 1-3 µm high. Archeopyle large and delta-isolinteloid. Size: length, excluding virgae, 69-95 µm, width at cingulum, excluding virgae, 70-95 µm.
--------------------------------------------------
Original diagnosis: de Verteuil and Norris, 1996, p. 152: Sumatradinium hamulatum
A species of Sumatradinium characterized by uniformly hamulate proximate luxuriae that do not form a complete reticulum; a cingulum clearly defined by two rows of low, hollow, conical or taeniate virgae; similar virgae aligned along select field boundaries, notably the apical intraseries boundaries and the posterior margin of the inferred third postcingular field; irregularly scattered, low, conical to evexate hollow virgae. Archeopyle large and delta-isolinteloid.
Original description: de Verteuil and Norris, 1996, p. 152: Sumatradinium hamulatum
Cysts proximate, intermediate, typically dorsoventrally compressed, peridinioid in outline and bipesioid. Hypocyst sides straight to convex with two short, symmetric, moderately pointed to rounded antapical lobes; antapical depression shallow to straight, rarely convex. Epicyst about equal to hypocyst, widest at cingulum with flanks straight to rounded convex in dorsovental view, forming an angle of about 120¦ at the apex. Cyst wider than broad, reniform in apical compression. In fresh specimens under TLM, the wall is less than 0.5µm thick, pigmented chestnut brown and comprises homogeneous pedium and proximate luxuriae. In other specimens the pigment is lost and the pedium expands to reveal inner and outer bounding strata with a narrow cavation between them. Both wall membranes are less than 0.1µm thick with the outer supporting the prismatic luxuriae. These consist of solid, curvilinear structural elements ca. 0.25µm thick and high and ca. 1.0 to 2.0µm long, that form a maze-like pattern or incomplete reticulum that may be termed hamulate (sensu Krutzsch 1959; in Punt et al. 1994). The hollow intratabular virgae are 0.75µm to 2.0µm in diameter proximally, generally closed distally, conical to evexate, and 1.0µm to 3.0µm in height. Peritabular virgae, particularly at the cingulum, are sometimes proximally joined or almost joined by low folds or thickenings of the tegillum, and may be taeniate parallel to field boundaries.
The cingulum is always clearly defined by two parallel, usually continuous, rows of evenly and closely spaced virgae; it is narrow (ca. 3 to 5µm wide), level, and about parallel to the cingular plane. To a lesser and variable extent, aligned virgae are present at the apex along the boundaries between the apical fields and sometimes also along 2'/1a and 4'/3a; on this basis four apical fields are inferred with the first apical being large and wide and the second and fourth apical fields correspondingly narrow. On the hypocyst, aligned virgae may be present along the posterior margin of the inferred third postcingular field of a standard peridinialean tabulation, extending also some way along 2"' /3"' and 3"'/4"'. The ends of the cingulum are separated by about four cingular widths, indicating that the sulcus is wide; two prominent, ellipsoid flagellar scars, one above the other, are present mid-ventrally below the level cingulum (pl. 16, fig. 5). Both are subspherical, the anterior being smaller, with their long axes parallel to the polar axis. The archeopyle is simple Type I involving mid-dorsal, large, iso-deltalinteloid *2a. Based on the position of the cingulum and the posterior archeopyle boundary, the inferred fourth precingular field is markedly latiplanate. Virgae are notably absent around the archeopyle and within the free opercular field.
Dimensions: Length, excluding virgae,69(82.5)95µm, holotype 86µm; width at cingulum, excluding virgae, 70(82.5)95µm, holotype 86µm. Thirty-five specimens measured.
Discussion: de Verteuil and Norris, 1996, p. 152
The uniformly hamulate wall sculpture of Sumatradinium hamulatum, in contrast to the development of a truly reticulate network as in Sumatradinium hispidum and other species in the genus, is worth noting. Sumatradinium hamulatum has its stratigraphic lowest occurrence at, or near, that for the genus and it does not appear to extend above the lower Miocene. The hamulate wall of this species may be an intermediate feature between a fully reticulate wall structure and a more Lejeunecysta-like wall with scattered virgae, as occurs for example in several informal taxa reported from the Oligocene of the Niger Delta by Biffi and Grignani (1983). This can be used to argue the affinity of Sumatradinium with the family Congruentidiaceae rather than with the subfamily Deflandreoideae within the family Peridiniaceae (Fensome et al.1993). Other evidence supports this hypothesis. Firstly, specimens of Sumatradinium hamulatum tend to have fairly straight sides and well defined, quite angular apical and antapical lobes, although rounded specimens more typical of Sumatradinium hispidum and Sumatradinium soucouyantiae do occur. This angular shape, with length about equal to width at the cingulum, is typical of Lejeunecysta, a protoperidinioid genus. Secondly, the cingulum delimited by virgae, and the selectively sculptured field boundaries at the apex and antapex, are also typical of several species within the protoperidinioid complex that have been grouped in the genus Cristadinium. Thirdly, the iso-deltalinteloid shape of the archeopyle in Sumatradinium hamulatum and Sumatradinium hispidum is typical of species of Lejeunecysta, for example Lejeunecysta lata Biffi and Grignani 1983, whereas Sumatradinium soucouyantiae and Sumatradinium druggii Lentin et al. 1994 tend to have a broader, lati-deltalinteloid archeopyle. Finally, the prominent flagella scars observed on the holotype of Sumatradinium hamulatum are almost identical in shape and relative size as those present on type material of Lejeunecysta lata, Trinovantedinium ferugnomatum and Trinovantedinium harpagonium, all considered to be within the Congruentidiaceae.
Comparison: de Verteuil and Norris, 1996, p. 152
The incomplete reticulum formed by the hamulate wall structure of Sumatradinium hamulatum is characteristic of Sumatradinium and separates the new species from others outside this genus. Only monotypic Erymnodinium has the same reticulate wall structure as Sumatradinium. Erymnodinium is distinguisthed from Sumatradinium only by the occurrence of peritabular crests, in contrast to nontabular processes or virgae. In the type species, middle to late Miocene Erymnodinium delectabile, well developed crests occur along selective field boundaries, notably the cingulum, the apical intraseries boundaries, and around the third postcingular field. The alignment of peritabular virgae in Sumatradinium hamulatum, which are proximally joined on some specimens, is suggestive of Erymnodinium, but the common nontabular virgae are indicative of Sumatradinium.
Among species of Sumatradinum, the new species is most similar to the type species, Sumatradinium hispidum. Sumatradinium hamulatum differs from Sumatradinium hispidum in having a consistently and uniformly incomplete reticulum shorter and fewer virgae, a clearly defined cingulum, virgae aligned along selective field boundaries and, most often, clearly defined antapical and apical lobes. Sumatradinium pustulosum has many uniformly distributed pustules that are generally wider
than they are high.
Occurrence: Lower Miocene (DN2 - DN3) in the Salisbury Embayment. Present to rare in the Popes Creek Sand Member and the Fairhaven Member of the Calvert Formation.
Holotype: de Verteuil and Norris, 1996, Plate 16, figs. 2-5
Locus typicus: Fairhaven Section, Herring Bay, Anne Arundel County, Maryland.
Type locality: Upper lower Miocene Fairhaven Member of the Calvert Formation.
--------------------------------------------------
G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999
Sumatradinium hamulatum de Verteuil and Norris, 1996a. Diagnosis from de Verteuil and Norris (1996a, p.152-153), A species of Sumatradinium characterized by uniformly hamulate proximate luxuriae that do not form a complete reticulum; a cingulum clearly defined by two rows of low, hollow, conical or taeniate virgae; similar virgae aligned along select field boundaries, notably the apical intraseries boundaries and the posterior margin of the inferred third postcingular field; irregularly scattered, low, conical to evexate hollow virgae. Virgae are 0.75-2 µm in diameter and 1-3 µm high. Archeopyle large and delta-isolinteloid. Size: length, excluding virgae, 69-95 µm, width at cingulum, excluding virgae, 70-95 µm.
--------------------------------------------------
Original diagnosis: de Verteuil and Norris, 1996, p. 152: Sumatradinium hamulatum
A species of Sumatradinium characterized by uniformly hamulate proximate luxuriae that do not form a complete reticulum; a cingulum clearly defined by two rows of low, hollow, conical or taeniate virgae; similar virgae aligned along select field boundaries, notably the apical intraseries boundaries and the posterior margin of the inferred third postcingular field; irregularly scattered, low, conical to evexate hollow virgae. Archeopyle large and delta-isolinteloid.
Original description: de Verteuil and Norris, 1996, p. 152: Sumatradinium hamulatum
Cysts proximate, intermediate, typically dorsoventrally compressed, peridinioid in outline and bipesioid. Hypocyst sides straight to convex with two short, symmetric, moderately pointed to rounded antapical lobes; antapical depression shallow to straight, rarely convex. Epicyst about equal to hypocyst, widest at cingulum with flanks straight to rounded convex in dorsovental view, forming an angle of about 120¦ at the apex. Cyst wider than broad, reniform in apical compression. In fresh specimens under TLM, the wall is less than 0.5µm thick, pigmented chestnut brown and comprises homogeneous pedium and proximate luxuriae. In other specimens the pigment is lost and the pedium expands to reveal inner and outer bounding strata with a narrow cavation between them. Both wall membranes are less than 0.1µm thick with the outer supporting the prismatic luxuriae. These consist of solid, curvilinear structural elements ca. 0.25µm thick and high and ca. 1.0 to 2.0µm long, that form a maze-like pattern or incomplete reticulum that may be termed hamulate (sensu Krutzsch 1959; in Punt et al. 1994). The hollow intratabular virgae are 0.75µm to 2.0µm in diameter proximally, generally closed distally, conical to evexate, and 1.0µm to 3.0µm in height. Peritabular virgae, particularly at the cingulum, are sometimes proximally joined or almost joined by low folds or thickenings of the tegillum, and may be taeniate parallel to field boundaries.
The cingulum is always clearly defined by two parallel, usually continuous, rows of evenly and closely spaced virgae; it is narrow (ca. 3 to 5µm wide), level, and about parallel to the cingular plane. To a lesser and variable extent, aligned virgae are present at the apex along the boundaries between the apical fields and sometimes also along 2'/1a and 4'/3a; on this basis four apical fields are inferred with the first apical being large and wide and the second and fourth apical fields correspondingly narrow. On the hypocyst, aligned virgae may be present along the posterior margin of the inferred third postcingular field of a standard peridinialean tabulation, extending also some way along 2"' /3"' and 3"'/4"'. The ends of the cingulum are separated by about four cingular widths, indicating that the sulcus is wide; two prominent, ellipsoid flagellar scars, one above the other, are present mid-ventrally below the level cingulum (pl. 16, fig. 5). Both are subspherical, the anterior being smaller, with their long axes parallel to the polar axis. The archeopyle is simple Type I involving mid-dorsal, large, iso-deltalinteloid *2a. Based on the position of the cingulum and the posterior archeopyle boundary, the inferred fourth precingular field is markedly latiplanate. Virgae are notably absent around the archeopyle and within the free opercular field.
Dimensions: Length, excluding virgae,69(82.5)95µm, holotype 86µm; width at cingulum, excluding virgae, 70(82.5)95µm, holotype 86µm. Thirty-five specimens measured.
Discussion: de Verteuil and Norris, 1996, p. 152
The uniformly hamulate wall sculpture of Sumatradinium hamulatum, in contrast to the development of a truly reticulate network as in Sumatradinium hispidum and other species in the genus, is worth noting. Sumatradinium hamulatum has its stratigraphic lowest occurrence at, or near, that for the genus and it does not appear to extend above the lower Miocene. The hamulate wall of this species may be an intermediate feature between a fully reticulate wall structure and a more Lejeunecysta-like wall with scattered virgae, as occurs for example in several informal taxa reported from the Oligocene of the Niger Delta by Biffi and Grignani (1983). This can be used to argue the affinity of Sumatradinium with the family Congruentidiaceae rather than with the subfamily Deflandreoideae within the family Peridiniaceae (Fensome et al.1993). Other evidence supports this hypothesis. Firstly, specimens of Sumatradinium hamulatum tend to have fairly straight sides and well defined, quite angular apical and antapical lobes, although rounded specimens more typical of Sumatradinium hispidum and Sumatradinium soucouyantiae do occur. This angular shape, with length about equal to width at the cingulum, is typical of Lejeunecysta, a protoperidinioid genus. Secondly, the cingulum delimited by virgae, and the selectively sculptured field boundaries at the apex and antapex, are also typical of several species within the protoperidinioid complex that have been grouped in the genus Cristadinium. Thirdly, the iso-deltalinteloid shape of the archeopyle in Sumatradinium hamulatum and Sumatradinium hispidum is typical of species of Lejeunecysta, for example Lejeunecysta lata Biffi and Grignani 1983, whereas Sumatradinium soucouyantiae and Sumatradinium druggii Lentin et al. 1994 tend to have a broader, lati-deltalinteloid archeopyle. Finally, the prominent flagella scars observed on the holotype of Sumatradinium hamulatum are almost identical in shape and relative size as those present on type material of Lejeunecysta lata, Trinovantedinium ferugnomatum and Trinovantedinium harpagonium, all considered to be within the Congruentidiaceae.
Comparison: de Verteuil and Norris, 1996, p. 152
The incomplete reticulum formed by the hamulate wall structure of Sumatradinium hamulatum is characteristic of Sumatradinium and separates the new species from others outside this genus. Only monotypic Erymnodinium has the same reticulate wall structure as Sumatradinium. Erymnodinium is distinguisthed from Sumatradinium only by the occurrence of peritabular crests, in contrast to nontabular processes or virgae. In the type species, middle to late Miocene Erymnodinium delectabile, well developed crests occur along selective field boundaries, notably the cingulum, the apical intraseries boundaries, and around the third postcingular field. The alignment of peritabular virgae in Sumatradinium hamulatum, which are proximally joined on some specimens, is suggestive of Erymnodinium, but the common nontabular virgae are indicative of Sumatradinium.
Among species of Sumatradinum, the new species is most similar to the type species, Sumatradinium hispidum. Sumatradinium hamulatum differs from Sumatradinium hispidum in having a consistently and uniformly incomplete reticulum shorter and fewer virgae, a clearly defined cingulum, virgae aligned along selective field boundaries and, most often, clearly defined antapical and apical lobes. Sumatradinium pustulosum has many uniformly distributed pustules that are generally wider
than they are high.
Occurrence: Lower Miocene (DN2 - DN3) in the Salisbury Embayment. Present to rare in the Popes Creek Sand Member and the Fairhaven Member of the Calvert Formation.