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Islandinium minutum subsp. barbatum
Islandinium minutum subsp. barbatum, Potvin, E. et al., 2018, p. 754-756
Holotype: Potvin, E. et al., 2018, Fig. 1A–F
Type locality: modern sediment, Western Arctic, East Siberian Sea
Original description: Potvin, E. et al., 2018,:
Diagnosis:
Cysts brown in colour, proximochorate to chorate, having spheroidal central body with a faintly to prominently granulate surface. Wall separation apparent only under process bases. Processes numerous, apparently non-tabular, erect or curved, slender, tapering distally,
unbranched, usually solid with small pericoel at base. Surface of processes smooth to finely granulate, bearing small barbs directed toward the central body. Process stems including bases generally circular in transverse section. Process tips taper to points usually minutely expanded into conjoined barbs. Principal archeopyle suture is the only clear expression of tabulation. Archeopyle apical and saphopylic, Type A3, formed by loss of three apical plates, 20, 30 and 40, with canal plate (and APC) sometimes also lost. Fourth apical plate (40) is large, occupying most
of the right side of the apical region; apical plates 20 and 30 occupy most of the left side of the apical region. Operculum free; opercular pieces released separately.
Description:
The cyst wall is brown in the type material (Fig. 1A–C,E–F, 2). The living cyst cell content appears slightly brown, and green globular bodies were present (Fig. 2A). The central body surface is faintly (the holotype) to prominently granulate (Fig. 1A,F, 2B–D, 3), with raised elements forming low verrucae or low coni about 0.1–0.6 µm in diameter and separated by about 0.2–0.9 µm (Fig. 1A,F, 2B–D, 3). Raised elements do not extend to process bases, which may be surrounded by a smooth ring under light microscopy (Fig. 1F, inset). Wall thickness is about 0.3 µm or less and there is no visible separation of layers between processes (Fig. 1C, 2E–H).
Processes: numerous, erect or curved, with a circular cross-section, and taper distally to minutely expanded tips (Fig. 1A–C,E–F, 2, 3). These tips may appear capitate under light microscopy (e.g. the holotype; Fig. 1A–C,E–F) but are resolved as conjoined barbs under the SEM (Fig. 3A–D).
The conjoined barbs are directed towards the central body surface, and occasionally curve toward the stem of the process, the tip of the process then appearing cauliflorate (Fig. 3D). Processes are irregularly distributed (Fig. 1A, 2B–D, 3A–B) but show no clear evidence of tabulation, with adjacent process bases separated from one another by 1.2–7.1 µm. Process bases are up to about 0.8–2.3 µm in diameter (Fig. 3E–F). Process length is relatively even for each specimen. Processes are solid except for a small pericoel usually present at process bases (apiculocavate condition sensu Evitt 1985, p. 65 but not his fig. 4.1, O) (Fig. 1B, 2E–H). Process length is about one-fifth to two-fifths of the central body diameter. Process stems are ornamented by numerous barbs that might appear as verrucae/granules in light microscopy (Fig. 1A–C, 2E–H). Barbs are directed towards the central body surface (Fig. 3B–D). Under SEM, minute granules have been observed on process stems, particularly at the proximate extremity (Fig. 3E). Observations under SEM also show a scalloped to smooth rim surrounding the base of some
processes (Fig. 3C,F; see also Fig. 1F, inset, for light microscope image).
The inner surface of the cyst is smooth (Fig. 3G).
Paratabulation: Principal archeopyle suture is the only clear expression of tabulation.
Archeopyle: saphopylic, Type A3, formed by loss of three apical plates, 2', 3' and 4' (Fig. 1D–F, 3H). The first apical plate (10) projects into the archeopyle (Fig. 1E, 3H). The canal plate (and presumably the APC) may be lost, or may remain attached to 1' (Fig. 1E, 3H). The fourth apical plate (4') is large and occupies most of the right side of the apical region, whereas 2' and 3' are somewhat smaller and occupy most
of the left side of the apical region (Fig. 1D–F, 3H). This results in a strongly asymmetrical epitabulation. A small but distinctive pointed spur on the left-lateral margin of the principal archeopyle suture marks the contact between plates 2' and 3' , along what is otherwise a nearly straight
line (Fig. 1F, 3H). In our material, the dorsal margin of 3' appears curved rather than sharply angled (Fig. 1F).
Operculum: free, and opercular pieces are released separately.
The cyst wall does not autofluoresce (exciter filter BP330-385; barrier filter BA420), which along with the brown coloration of the wall is consistent with the interpretation that this species is heterotrophic.
Dimensions:
Holotype: central body diameter, 38 9 40 µm, process length 9.1–10.9 (average 10.0) µm;
Range: central body maximum diameter, 25 (33.2) 44 µm, standard deviation 4.9 µm; average process length, 6.8 (9.8) 12.9 µm, standard deviation 1.5 µm; 50 specimens measured.
Other material (Head et al. 2001), Kara Sea: Range: central body maximum diameter, 34 (42.5) 51 µm, standard deviation 6.7 µm; average process length, 7.5 (9.9) 11.0 µm, standard deviation 1.3 µm; 6 specimens measured
Affinities/Comparison:
The phylogenetic association between I. minutum subsp. barbatum and I. minutum subsp. minutum prompted a morphological re-examination of specimens in the Western Arctic, and Labrador and Kara seas. In I. minutum subsp. minutum, the process extremities are acuminate
and the process surfaces are smooth under light microscopy (Fig. 7A–C, 8A–C). The surface of the central body is granulate and the distribution of the processes is irregular (Fig. 7B–G, 8A–C). However, under SEM, the process surfaces appear finely granulate at low magnification
(Fig. 7D,F) but reduced barbs are seen at high magnification (Fig. 7E,G–I). Granulation at the surface of the process was also observed (Fig. 7H–I). A scalloped to smooth rim may surround the process bases (Fig. 7E,G,I). Conjoined barbs at the distal extremities of processes were occasionally observed (Fig. 7E). These observations under SEM bring I. minutum subsp. minutum closer to I. minutum subsp. barbatum than any other RBSCs. However, barbs are more prominently developed on I. minutum subsp. barbatum, and processes are generally longer
and more widely spaced (Fig. 1, 2, 3, 7, 8A–C). These two subspecies can therefore be differentiated under the light microscope.
Specimens of I. minutum subsp. minutum from the Western Arctic and Labrador Sea were also sequenced. Based on the SSU rDNA and LSU rDNA (Fig. 4–5), the phylogenetic position of I. minutum subsp. minutum from the Western Arctic and the Labrador Sea accorded with specimens from Baffin Bay (Potvin et al. 2013) and Barrow Strait, Nunavik, Canada (Mertens et al. 2013).
Holotype: Potvin, E. et al., 2018, Fig. 1A–F
Type locality: modern sediment, Western Arctic, East Siberian Sea
Original description: Potvin, E. et al., 2018,:
Diagnosis:
Cysts brown in colour, proximochorate to chorate, having spheroidal central body with a faintly to prominently granulate surface. Wall separation apparent only under process bases. Processes numerous, apparently non-tabular, erect or curved, slender, tapering distally,
unbranched, usually solid with small pericoel at base. Surface of processes smooth to finely granulate, bearing small barbs directed toward the central body. Process stems including bases generally circular in transverse section. Process tips taper to points usually minutely expanded into conjoined barbs. Principal archeopyle suture is the only clear expression of tabulation. Archeopyle apical and saphopylic, Type A3, formed by loss of three apical plates, 20, 30 and 40, with canal plate (and APC) sometimes also lost. Fourth apical plate (40) is large, occupying most
of the right side of the apical region; apical plates 20 and 30 occupy most of the left side of the apical region. Operculum free; opercular pieces released separately.
Description:
The cyst wall is brown in the type material (Fig. 1A–C,E–F, 2). The living cyst cell content appears slightly brown, and green globular bodies were present (Fig. 2A). The central body surface is faintly (the holotype) to prominently granulate (Fig. 1A,F, 2B–D, 3), with raised elements forming low verrucae or low coni about 0.1–0.6 µm in diameter and separated by about 0.2–0.9 µm (Fig. 1A,F, 2B–D, 3). Raised elements do not extend to process bases, which may be surrounded by a smooth ring under light microscopy (Fig. 1F, inset). Wall thickness is about 0.3 µm or less and there is no visible separation of layers between processes (Fig. 1C, 2E–H).
Processes: numerous, erect or curved, with a circular cross-section, and taper distally to minutely expanded tips (Fig. 1A–C,E–F, 2, 3). These tips may appear capitate under light microscopy (e.g. the holotype; Fig. 1A–C,E–F) but are resolved as conjoined barbs under the SEM (Fig. 3A–D).
The conjoined barbs are directed towards the central body surface, and occasionally curve toward the stem of the process, the tip of the process then appearing cauliflorate (Fig. 3D). Processes are irregularly distributed (Fig. 1A, 2B–D, 3A–B) but show no clear evidence of tabulation, with adjacent process bases separated from one another by 1.2–7.1 µm. Process bases are up to about 0.8–2.3 µm in diameter (Fig. 3E–F). Process length is relatively even for each specimen. Processes are solid except for a small pericoel usually present at process bases (apiculocavate condition sensu Evitt 1985, p. 65 but not his fig. 4.1, O) (Fig. 1B, 2E–H). Process length is about one-fifth to two-fifths of the central body diameter. Process stems are ornamented by numerous barbs that might appear as verrucae/granules in light microscopy (Fig. 1A–C, 2E–H). Barbs are directed towards the central body surface (Fig. 3B–D). Under SEM, minute granules have been observed on process stems, particularly at the proximate extremity (Fig. 3E). Observations under SEM also show a scalloped to smooth rim surrounding the base of some
processes (Fig. 3C,F; see also Fig. 1F, inset, for light microscope image).
The inner surface of the cyst is smooth (Fig. 3G).
Paratabulation: Principal archeopyle suture is the only clear expression of tabulation.
Archeopyle: saphopylic, Type A3, formed by loss of three apical plates, 2', 3' and 4' (Fig. 1D–F, 3H). The first apical plate (10) projects into the archeopyle (Fig. 1E, 3H). The canal plate (and presumably the APC) may be lost, or may remain attached to 1' (Fig. 1E, 3H). The fourth apical plate (4') is large and occupies most of the right side of the apical region, whereas 2' and 3' are somewhat smaller and occupy most
of the left side of the apical region (Fig. 1D–F, 3H). This results in a strongly asymmetrical epitabulation. A small but distinctive pointed spur on the left-lateral margin of the principal archeopyle suture marks the contact between plates 2' and 3' , along what is otherwise a nearly straight
line (Fig. 1F, 3H). In our material, the dorsal margin of 3' appears curved rather than sharply angled (Fig. 1F).
Operculum: free, and opercular pieces are released separately.
The cyst wall does not autofluoresce (exciter filter BP330-385; barrier filter BA420), which along with the brown coloration of the wall is consistent with the interpretation that this species is heterotrophic.
Dimensions:
Holotype: central body diameter, 38 9 40 µm, process length 9.1–10.9 (average 10.0) µm;
Range: central body maximum diameter, 25 (33.2) 44 µm, standard deviation 4.9 µm; average process length, 6.8 (9.8) 12.9 µm, standard deviation 1.5 µm; 50 specimens measured.
Other material (Head et al. 2001), Kara Sea: Range: central body maximum diameter, 34 (42.5) 51 µm, standard deviation 6.7 µm; average process length, 7.5 (9.9) 11.0 µm, standard deviation 1.3 µm; 6 specimens measured
Affinities/Comparison:
The phylogenetic association between I. minutum subsp. barbatum and I. minutum subsp. minutum prompted a morphological re-examination of specimens in the Western Arctic, and Labrador and Kara seas. In I. minutum subsp. minutum, the process extremities are acuminate
and the process surfaces are smooth under light microscopy (Fig. 7A–C, 8A–C). The surface of the central body is granulate and the distribution of the processes is irregular (Fig. 7B–G, 8A–C). However, under SEM, the process surfaces appear finely granulate at low magnification
(Fig. 7D,F) but reduced barbs are seen at high magnification (Fig. 7E,G–I). Granulation at the surface of the process was also observed (Fig. 7H–I). A scalloped to smooth rim may surround the process bases (Fig. 7E,G,I). Conjoined barbs at the distal extremities of processes were occasionally observed (Fig. 7E). These observations under SEM bring I. minutum subsp. minutum closer to I. minutum subsp. barbatum than any other RBSCs. However, barbs are more prominently developed on I. minutum subsp. barbatum, and processes are generally longer
and more widely spaced (Fig. 1, 2, 3, 7, 8A–C). These two subspecies can therefore be differentiated under the light microscope.
Specimens of I. minutum subsp. minutum from the Western Arctic and Labrador Sea were also sequenced. Based on the SSU rDNA and LSU rDNA (Fig. 4–5), the phylogenetic position of I. minutum subsp. minutum from the Western Arctic and the Labrador Sea accorded with specimens from Baffin Bay (Potvin et al. 2013) and Barrow Strait, Nunavik, Canada (Mertens et al. 2013).