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Spiculodinium
From Fensome et al., 2019:
Spiculodinium
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Original description Duxbury, 2018:
Type species: Spiculodinium neptuni (Eisenack 1958, p. 399, Plate 26, Figures 7, 8; text-figure 8) Duxbury n. gen. n. comb.
Type: Eisenack 1958, pl. 26. fig. 7, as Baltisphaeridium neptuni.
Derivation of Name: From the Latin spiculo, -atus, sharpen to a point – in reference to the characteristic distal process terminations
Diagnosis: Spheroidal to ellipsoidal gonyaulacoid dinocysts bearing a moderate number of processes each with sharplypointed distal terminations. Gonal and sutural processes may be present, discrete or joined proximally by ridges or crests. The surface of the central body is micro-reticulate to fibrous and low ridges may extend from the surface onto the processes. Archeopyle mid-dorsal, single-plate precingular (3'') with the operculum bearing a mesotabular, hollow process similar in length to the others.
Remarks: The taxonomy of the type species of this genus, Spiculodinium neptuni (Eisenack 1958) Duxbury n. gen. n. comb. has been debated for some time with the most recent arguments being between the genera Spiniferites Mantell 1850 emend. Sarjeant 1970 and Achomosphaera Evitt 1963 (see comments below). Duxbury (1983) synonymised Achomosphaera with Spiniferites, following Reid (1974) and May (1980) for reasons explained in Duxbury (1983, pp. 54, 55), and that approach has again been followed here. Comments below therefore include species formerly included in Achomosphaera.
For several reasons, the present author considers Spiculodinium neptuni and the similar species S. alatum (Duxbury 1977) n. gen. n. comb. sufficiently different from Spiniferites to merit their removal to Spiculodinium n. gen. Although both possess gonal and sutural processes, the process terminations are simple spikes, not typical of Spiniferites. The gonal processes in Spiculodinium are usually trifurcate and can bear four spines, but sutural processes are bifurcate. The typically large size and micro-reticulate to fibrous body texture are also characteristic of Spiculodinium n. gen., as are the surface ridges which extend onto process bases, reminiscent of the genus Kleithriasphaeridium Davey 1974.
It is very uncommon to see the operculum of Spiculodinium neptuni, this being usually lost, and out of thousands of specimens recorded in the current study, only three were observed. A remarkable feature is the presence of an opercular process (text-fig. 9, Plate 8, Figures 1-3) which is mesotabular, distally digitate, hollow, apparently open-ended and reminiscent of some species of the genus Kleithriasphaeridium Davey 1974,
most notably K. corrugatum Davey 1974. This contrasts markedly with the distally closed tri- and –bifurcate gonal processes.
The presence of a long, mesotabular opercular process is not a feature typical of Spiniferites (or Achomosphaera). Spiculodinium neptuni and S. alatus range much older than any species assigned to the genus Spiniferites. The first has been recorded to the base of the Cromer Knoll Group, Valhall Formation at Speeton (Bed D7F, text-figure 2) and in the Central North Sea. The FAD of Spiniferites spp., including S. primaevus (Duxbury 1977) Monteil 1991 and S. twistringiensis (Maier 1959) Fensome et al. 1990, is within the lower Valanginian; at Speeton, Bed D4B, paratollia Zone (text-fig. 2). These younger species contrast markedly with Spiculodinium neptuni and S. alatum in possessing smooth cyst walls and being significantly smaller. In addition, Spiniferites twistringiensis is the oldest species to have “typical” blade-like terminations to the gonal and sutural spines, as opposed to the spiny terminations of Spiculodinium neptuni and S. alatum and the irregular terminations of S. primaevus.
Despite the long stratigraphic range of Spiculodinium n. gen. (at least late Berriasian to Aptian), it was remarkably stable in morphology, and never developed distal linking trabeculae; this contrasts with species of Spiniferites, in which such features are an early development. Nematosphaeropsis compositus Duxbury n. sp. and Nematosphaeropsis scala Duxbury 1977 are similar to S. twistringiensis and S. primaevus respectively, and all four species appear in the Valanginian.
Spiculodinium
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Original description Duxbury, 2018:
Type species: Spiculodinium neptuni (Eisenack 1958, p. 399, Plate 26, Figures 7, 8; text-figure 8) Duxbury n. gen. n. comb.
Type: Eisenack 1958, pl. 26. fig. 7, as Baltisphaeridium neptuni.
Derivation of Name: From the Latin spiculo, -atus, sharpen to a point – in reference to the characteristic distal process terminations
Diagnosis: Spheroidal to ellipsoidal gonyaulacoid dinocysts bearing a moderate number of processes each with sharplypointed distal terminations. Gonal and sutural processes may be present, discrete or joined proximally by ridges or crests. The surface of the central body is micro-reticulate to fibrous and low ridges may extend from the surface onto the processes. Archeopyle mid-dorsal, single-plate precingular (3'') with the operculum bearing a mesotabular, hollow process similar in length to the others.
Remarks: The taxonomy of the type species of this genus, Spiculodinium neptuni (Eisenack 1958) Duxbury n. gen. n. comb. has been debated for some time with the most recent arguments being between the genera Spiniferites Mantell 1850 emend. Sarjeant 1970 and Achomosphaera Evitt 1963 (see comments below). Duxbury (1983) synonymised Achomosphaera with Spiniferites, following Reid (1974) and May (1980) for reasons explained in Duxbury (1983, pp. 54, 55), and that approach has again been followed here. Comments below therefore include species formerly included in Achomosphaera.
For several reasons, the present author considers Spiculodinium neptuni and the similar species S. alatum (Duxbury 1977) n. gen. n. comb. sufficiently different from Spiniferites to merit their removal to Spiculodinium n. gen. Although both possess gonal and sutural processes, the process terminations are simple spikes, not typical of Spiniferites. The gonal processes in Spiculodinium are usually trifurcate and can bear four spines, but sutural processes are bifurcate. The typically large size and micro-reticulate to fibrous body texture are also characteristic of Spiculodinium n. gen., as are the surface ridges which extend onto process bases, reminiscent of the genus Kleithriasphaeridium Davey 1974.
It is very uncommon to see the operculum of Spiculodinium neptuni, this being usually lost, and out of thousands of specimens recorded in the current study, only three were observed. A remarkable feature is the presence of an opercular process (text-fig. 9, Plate 8, Figures 1-3) which is mesotabular, distally digitate, hollow, apparently open-ended and reminiscent of some species of the genus Kleithriasphaeridium Davey 1974,
most notably K. corrugatum Davey 1974. This contrasts markedly with the distally closed tri- and –bifurcate gonal processes.
The presence of a long, mesotabular opercular process is not a feature typical of Spiniferites (or Achomosphaera). Spiculodinium neptuni and S. alatus range much older than any species assigned to the genus Spiniferites. The first has been recorded to the base of the Cromer Knoll Group, Valhall Formation at Speeton (Bed D7F, text-figure 2) and in the Central North Sea. The FAD of Spiniferites spp., including S. primaevus (Duxbury 1977) Monteil 1991 and S. twistringiensis (Maier 1959) Fensome et al. 1990, is within the lower Valanginian; at Speeton, Bed D4B, paratollia Zone (text-fig. 2). These younger species contrast markedly with Spiculodinium neptuni and S. alatum in possessing smooth cyst walls and being significantly smaller. In addition, Spiniferites twistringiensis is the oldest species to have “typical” blade-like terminations to the gonal and sutural spines, as opposed to the spiny terminations of Spiculodinium neptuni and S. alatum and the irregular terminations of S. primaevus.
Despite the long stratigraphic range of Spiculodinium n. gen. (at least late Berriasian to Aptian), it was remarkably stable in morphology, and never developed distal linking trabeculae; this contrasts with species of Spiniferites, in which such features are an early development. Nematosphaeropsis compositus Duxbury n. sp. and Nematosphaeropsis scala Duxbury 1977 are similar to S. twistringiensis and S. primaevus respectively, and all four species appear in the Valanginian.