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Islandinium pacificum
Islandinium pacificum sp. nov.; Gurdebeke, P.R et al. 2019
Holotype: Gurdebeke, P.R et al. 2019, Plate 1, figure 1–6
Age: Pleistocene to Modern
Stratigraphic range: uppermost Pleistocene, Holocene, Eemian, modern sediments
Original description: Gurdebeke, P.R et al. 2019, p.7: Islandinium pacificum sp. nov:
Diagnosis: Light brown spherical spiny cyst; proximochorate to chorate; spherical smooth central body. Cyst wall shows no visible separation, except at the processes, which are numerous, long (~10 µm) and with random and non-tabular arrangement; erect or recurved; slender, acuminate and unbranched; circular cross-section over its length and apiculocavate. Process surface smooth, harpoon-like, bearing fine barbs directed toward the cyst center. Archeopyle apical and saphopylic, corresponding to three apical plates (20, 30 and 40; type A3). Operculum adnate. No other traces of tabulation are reflected on the cyst.
Description:
Cyst light brown and often strongly folded when empty. No visible separation of the thin (< 0.2 mm), smooth wall, except at the hollow process bases.
Wall: smooth only, not smooth to scabrate, as suggested by Radi et al. (2013)
Central body: ornamented with numerous erect or curved processes
Processes: of 7.4 to 12.7 µm long (22 to 43% of central body diameter), base of the processes is circular with a diameter of 0.7 µm (N=9), cross-sections are circular along the length of a process, processes taper distally to acuminate tips, base of the process is hollow, with the length of the cavity being 1–2 µm, corresponding to about 15% of the total process length. SEM observations reveal the processes bear fine barbs that point in a proximal direction. In LM, the barbs are mostly observed as simple granules. Apart from the barbs, the processes are smooth. The distal barbs may be joined and give the appearance of a slight expansion of the process tips, which are in reality acuminate. The processes appear to be irregularly distributed and show no evidence of tabulation. Process bases are spaced 2.1 (2.8) 4.4 µm (N = 19) apart for Eemian specimens, and 2.3 (3.4) 4.0 µm (N = 6) apart for Holocene specimens. Density of processes is ~11 per 10*10 µm2.
Archeopyle: saphopylic, formed by the loss of three apical plates (type A3): 2', 3' and 4' ; archeopyle suture is the only evidence of tabulation and is often not visible due to folding of the cyst. The first apical plate projects into the archeopyle and the X-Po plates may remain attached. Plate 4' forms the largest (right) part of the archeopyle, with
plates 3' and 4' forming the smaller left side of the archeopyle. Living cysts contain a thick endospore.
Dimensions:
Holotype: central body diameter: 41.5 µm; process length: 11.9 µm.
Overall range: central body diameter: 25.0 (35.6) 46.0 µm (N = 51), process length: 6.0 (10.5) 14.0 µm (N = 43)
Holocene and modern sediments from the northeast Pacific: central body diameter: 28.9 (35.6) 42.2 µm, process length: 7.4 (10.3) 12.7 µm (N = 17)
Eemian of the Vøring Plateau: central body diameter: 25.0 (35.9) 46.0 µm (N = 35), process length: 9.0 (10.8) 14.0 µm (N = 27)
Occurrence: The species occurs in the uppermost Pleistocene, Holocene and modern sediments of the temperate zones of the northeast Pacific Ocean, and during the last interglacial also in the northern North Atlantic Ocean.
Remarks: The cyst described as ‘Cyst type M1’ in Bringueé et al. (2013, pl. 2, fig. 4) may be Islandinium pacificum, but barbs are not described or visible in the illustrations so this identification cannot be confirmed here.
Affinities/Discussion:
Motile stage for Islandinium pacificum sp. nov. is Protoperidinium mutsuense
Islandinium pacificum can be mostly distinguished from other RBPCs by the presence of barbs on the processes of I. pacificum; processes of I. minutum subsp. minutum have a microgranular surface but rarely barbs. Islandinium pacificum sp.nov. is most similar to Islandinium minutum subsp. barbatum, from which it is distinguished by its smooth wall. I. minutum subsp. barbatum. (Potvin et al. 2017) have conspicuous barbs and a similar size range (central body diameter and process length) but can be distinguished from I. pacificum by its granular central body wall (faintly to prominently granular surface texture).
Islandinium cezare differs by its characteristic expanded process terminations and its finely granular central body wall surface, and I. brevispinosum by its markedly shorter processes and the relatively small central body diameter.
The size, process morphology and the saphopylic, polyplacoid archeopyle in I. pacificum distinguishes it from Echinidinium species, which have a chasmic archeopyle. Echinidinium granulatum differs from all Islandinium species in having a granular wall and granular processes instead of recurved barbs. Processes of Echinidinium delicatum are hollow over the entire length, and Echinidinium aculeatum has aculeate processes. The latter two Echinidinium species are smaller than I. pacificum. Echinidinium karaense also has a smooth central body wall surface and apiculocavate processes, but the processes are conical to tapering, slightly shorter and smooth, bearing no barbs.
Cysts of Protoperidinium tricingulatum have a theropylic archeopyle and capitate process terminations (Kawami et al.2009). Cysts of Protoperidinium lewisiae, which also bear apiculocavate processes (Mertens et al. 2015), differ from Islandinium pacificum in having a theropylic archeopyle and being generally smaller while having more densely implanted processes. The tiny spinules on the processes of cysts of P. lewisiae, which might resemble barbs, are hard to observe using LM, whereas they are easily visible for Islandinium pacificum under LM. While having similar dimensions, cysts of Niea acanthocysta are different from Islandinium pacificum in having a microgranular wall and solid, often recurved processes (Mertens et al. 2015; Liuet al. 2015b).
Holotype: Gurdebeke, P.R et al. 2019, Plate 1, figure 1–6
Age: Pleistocene to Modern
Stratigraphic range: uppermost Pleistocene, Holocene, Eemian, modern sediments
Original description: Gurdebeke, P.R et al. 2019, p.7: Islandinium pacificum sp. nov:
Diagnosis: Light brown spherical spiny cyst; proximochorate to chorate; spherical smooth central body. Cyst wall shows no visible separation, except at the processes, which are numerous, long (~10 µm) and with random and non-tabular arrangement; erect or recurved; slender, acuminate and unbranched; circular cross-section over its length and apiculocavate. Process surface smooth, harpoon-like, bearing fine barbs directed toward the cyst center. Archeopyle apical and saphopylic, corresponding to three apical plates (20, 30 and 40; type A3). Operculum adnate. No other traces of tabulation are reflected on the cyst.
Description:
Cyst light brown and often strongly folded when empty. No visible separation of the thin (< 0.2 mm), smooth wall, except at the hollow process bases.
Wall: smooth only, not smooth to scabrate, as suggested by Radi et al. (2013)
Central body: ornamented with numerous erect or curved processes
Processes: of 7.4 to 12.7 µm long (22 to 43% of central body diameter), base of the processes is circular with a diameter of 0.7 µm (N=9), cross-sections are circular along the length of a process, processes taper distally to acuminate tips, base of the process is hollow, with the length of the cavity being 1–2 µm, corresponding to about 15% of the total process length. SEM observations reveal the processes bear fine barbs that point in a proximal direction. In LM, the barbs are mostly observed as simple granules. Apart from the barbs, the processes are smooth. The distal barbs may be joined and give the appearance of a slight expansion of the process tips, which are in reality acuminate. The processes appear to be irregularly distributed and show no evidence of tabulation. Process bases are spaced 2.1 (2.8) 4.4 µm (N = 19) apart for Eemian specimens, and 2.3 (3.4) 4.0 µm (N = 6) apart for Holocene specimens. Density of processes is ~11 per 10*10 µm2.
Archeopyle: saphopylic, formed by the loss of three apical plates (type A3): 2', 3' and 4' ; archeopyle suture is the only evidence of tabulation and is often not visible due to folding of the cyst. The first apical plate projects into the archeopyle and the X-Po plates may remain attached. Plate 4' forms the largest (right) part of the archeopyle, with
plates 3' and 4' forming the smaller left side of the archeopyle. Living cysts contain a thick endospore.
Dimensions:
Holotype: central body diameter: 41.5 µm; process length: 11.9 µm.
Overall range: central body diameter: 25.0 (35.6) 46.0 µm (N = 51), process length: 6.0 (10.5) 14.0 µm (N = 43)
Holocene and modern sediments from the northeast Pacific: central body diameter: 28.9 (35.6) 42.2 µm, process length: 7.4 (10.3) 12.7 µm (N = 17)
Eemian of the Vøring Plateau: central body diameter: 25.0 (35.9) 46.0 µm (N = 35), process length: 9.0 (10.8) 14.0 µm (N = 27)
Occurrence: The species occurs in the uppermost Pleistocene, Holocene and modern sediments of the temperate zones of the northeast Pacific Ocean, and during the last interglacial also in the northern North Atlantic Ocean.
Remarks: The cyst described as ‘Cyst type M1’ in Bringueé et al. (2013, pl. 2, fig. 4) may be Islandinium pacificum, but barbs are not described or visible in the illustrations so this identification cannot be confirmed here.
Affinities/Discussion:
Motile stage for Islandinium pacificum sp. nov. is Protoperidinium mutsuense
Islandinium pacificum can be mostly distinguished from other RBPCs by the presence of barbs on the processes of I. pacificum; processes of I. minutum subsp. minutum have a microgranular surface but rarely barbs. Islandinium pacificum sp.nov. is most similar to Islandinium minutum subsp. barbatum, from which it is distinguished by its smooth wall. I. minutum subsp. barbatum. (Potvin et al. 2017) have conspicuous barbs and a similar size range (central body diameter and process length) but can be distinguished from I. pacificum by its granular central body wall (faintly to prominently granular surface texture).
Islandinium cezare differs by its characteristic expanded process terminations and its finely granular central body wall surface, and I. brevispinosum by its markedly shorter processes and the relatively small central body diameter.
The size, process morphology and the saphopylic, polyplacoid archeopyle in I. pacificum distinguishes it from Echinidinium species, which have a chasmic archeopyle. Echinidinium granulatum differs from all Islandinium species in having a granular wall and granular processes instead of recurved barbs. Processes of Echinidinium delicatum are hollow over the entire length, and Echinidinium aculeatum has aculeate processes. The latter two Echinidinium species are smaller than I. pacificum. Echinidinium karaense also has a smooth central body wall surface and apiculocavate processes, but the processes are conical to tapering, slightly shorter and smooth, bearing no barbs.
Cysts of Protoperidinium tricingulatum have a theropylic archeopyle and capitate process terminations (Kawami et al.2009). Cysts of Protoperidinium lewisiae, which also bear apiculocavate processes (Mertens et al. 2015), differ from Islandinium pacificum in having a theropylic archeopyle and being generally smaller while having more densely implanted processes. The tiny spinules on the processes of cysts of P. lewisiae, which might resemble barbs, are hard to observe using LM, whereas they are easily visible for Islandinium pacificum under LM. While having similar dimensions, cysts of Niea acanthocysta are different from Islandinium pacificum in having a microgranular wall and solid, often recurved processes (Mertens et al. 2015; Liuet al. 2015b).