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Algidasphaeridium euaxum
From Fensome et al., 2019:
Algidasphaeridium? euaxum, Head, 1993, p.24,26, fig.16, nos.1–8,11; fig.26, no.4.
Holotype: Head, 1993, fig.16, no.11.
NOW Echinidinium.
Originally Algidasphaeridium?, subsequently (and now) Echinidinium.
Questionable assignment: Head (1993, p.24).
Age: latest Pliocene.
Locus typicus: St. Erth Beds, Cornwall, SW England
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Original description: [Head, 1993, p.24]:
Diagnosis:
Cysts skolochorate, biphragmal, medium to dark brown in color, with spherical to subspherical central body. Wall layers closely appressed except at process bases; endophragm surface faintly granulate to scabrate; periphragm smooth. Processes fairly evenly distributed over cyst surface, are periphragmal, hollow, distally closed, have circular transverse cross section, smooth surface, and taper distally, ending in short bifid tips. Archeopyle chasmic. Paratabular features absent.
Description:
Endophragm and periphragm separated only at base of processes: no other indication of wall layer separation seen.
Wall thickness generally much less than 0.5 µm (including holotype) but on some specimens may be up to about 0.7 µm. Endophragm surface faintly granulate (low rounded bumps, about 0.2-0.3 µm in diameter, and fairly regularly distributed) or scabrate, ornament often becoming less apparent (seemingly almost smooth) on some specimens including the holotype and especially on thicker walled specimens.
Process distribution shows no clear reflection of tabulation. Processes long and narrow (around 1.0-2.0 µm wide) tapering to minutely platformed (bifid?) tips; these may be flat, flared, or slightly recurved. Platforms about 2 µm or less in diameter. Some cysts observed with a few slender processes co-occurring with those of normal width. Processes typically broken at some point along shafts, and of 103 specimens examined in detail, none apparently has escaped some process breakage (see also Comparison section, below). Occasional long acuminate processes are possibly primary features. Clear indications of excystment aperture rarely seen.
Archeopyle infrequently an approximately U-shaped rupture and interpreted as chasmic.
Dimensions:
Holotype: central body diameter, 48 X 38 µm; average process length, 11 µm.
Range: central body diameter, 30(39.4)52 µm; average process length, 7(11.5)17 µm.
24 specimens measured.
Affinities: (p.24-25):
Multispinula sp. of LeNoir and Hart (1986) are considered conspecific with A.? euaxum. Notably, distally furcate terminations were sometimes observed (Duffield and Stein, 1986, p. 34) and illustrated specimens show the typically blunt processes that are here interpreted to be caused by breakage. A specimen from Recent sediments of northwestern Australia and illustrated as Multispinula sp. by Bint (1988, fig. 4B) is also similar to A.? euaxum. The processes are rather small but this specimen is part of a plexus of morphologies (as Multispinula spp., in Bint, 1988, p. 333).
\par Algidasphaeridium? minutum (Harland and Reid in Harland et al., 1980) Matsuoka and Bujak, 1988, described from Recent and sub-Recent sediments of the Beaufort Sea, Canadian Arctic, has processes that are solid rather than hollow, aculeate rather than bifid, and somewhat smaller (length, 3.75-8.75 µm) than for A. euaxum. Algidasphaeridium capillatum Matsuoka and Bujak, 1988, described from upper Miocene deposits of the Bering Sea, differs from A. euaxum in having shorter, hair-like solid processes and an unpigmented wall. In placing Algidasphaeridium in the order Gymnodiniales, Matsuoka and Bujak (1988) noted that a chasmic archeopyle occurs not only in the type species, A. capillatum, but also in modern cysts of Pheopolykrikos hartmannii (Matsuoka and Fukuyo, 1986), Cochlodinium sp. of Matsuoka (1985a), and Gymnodinium catenatum Graham, 1943, emend. Anderson et al., 1988. It should also be noted that Pheopolykrikos hartmannii and Cochlodinium sp. of Matsuoka (1985a) both have brownpigmented cyst walls (Matsuoka,1985), as does Gymnodinium catenatum (Anderson et al., 1988).
Algidasphaeridium? euaxum, Head, 1993, p.24,26, fig.16, nos.1–8,11; fig.26, no.4.
Holotype: Head, 1993, fig.16, no.11.
NOW Echinidinium.
Originally Algidasphaeridium?, subsequently (and now) Echinidinium.
Questionable assignment: Head (1993, p.24).
Age: latest Pliocene.
Locus typicus: St. Erth Beds, Cornwall, SW England
---------------------------------------------------------------------------------------------------
Original description: [Head, 1993, p.24]:
Diagnosis:
Cysts skolochorate, biphragmal, medium to dark brown in color, with spherical to subspherical central body. Wall layers closely appressed except at process bases; endophragm surface faintly granulate to scabrate; periphragm smooth. Processes fairly evenly distributed over cyst surface, are periphragmal, hollow, distally closed, have circular transverse cross section, smooth surface, and taper distally, ending in short bifid tips. Archeopyle chasmic. Paratabular features absent.
Description:
Endophragm and periphragm separated only at base of processes: no other indication of wall layer separation seen.
Wall thickness generally much less than 0.5 µm (including holotype) but on some specimens may be up to about 0.7 µm. Endophragm surface faintly granulate (low rounded bumps, about 0.2-0.3 µm in diameter, and fairly regularly distributed) or scabrate, ornament often becoming less apparent (seemingly almost smooth) on some specimens including the holotype and especially on thicker walled specimens.
Process distribution shows no clear reflection of tabulation. Processes long and narrow (around 1.0-2.0 µm wide) tapering to minutely platformed (bifid?) tips; these may be flat, flared, or slightly recurved. Platforms about 2 µm or less in diameter. Some cysts observed with a few slender processes co-occurring with those of normal width. Processes typically broken at some point along shafts, and of 103 specimens examined in detail, none apparently has escaped some process breakage (see also Comparison section, below). Occasional long acuminate processes are possibly primary features. Clear indications of excystment aperture rarely seen.
Archeopyle infrequently an approximately U-shaped rupture and interpreted as chasmic.
Dimensions:
Holotype: central body diameter, 48 X 38 µm; average process length, 11 µm.
Range: central body diameter, 30(39.4)52 µm; average process length, 7(11.5)17 µm.
24 specimens measured.
Affinities: (p.24-25):
Multispinula sp. of LeNoir and Hart (1986) are considered conspecific with A.? euaxum. Notably, distally furcate terminations were sometimes observed (Duffield and Stein, 1986, p. 34) and illustrated specimens show the typically blunt processes that are here interpreted to be caused by breakage. A specimen from Recent sediments of northwestern Australia and illustrated as Multispinula sp. by Bint (1988, fig. 4B) is also similar to A.? euaxum. The processes are rather small but this specimen is part of a plexus of morphologies (as Multispinula spp., in Bint, 1988, p. 333).
\par Algidasphaeridium? minutum (Harland and Reid in Harland et al., 1980) Matsuoka and Bujak, 1988, described from Recent and sub-Recent sediments of the Beaufort Sea, Canadian Arctic, has processes that are solid rather than hollow, aculeate rather than bifid, and somewhat smaller (length, 3.75-8.75 µm) than for A. euaxum. Algidasphaeridium capillatum Matsuoka and Bujak, 1988, described from upper Miocene deposits of the Bering Sea, differs from A. euaxum in having shorter, hair-like solid processes and an unpigmented wall. In placing Algidasphaeridium in the order Gymnodiniales, Matsuoka and Bujak (1988) noted that a chasmic archeopyle occurs not only in the type species, A. capillatum, but also in modern cysts of Pheopolykrikos hartmannii (Matsuoka and Fukuyo, 1986), Cochlodinium sp. of Matsuoka (1985a), and Gymnodinium catenatum Graham, 1943, emend. Anderson et al., 1988. It should also be noted that Pheopolykrikos hartmannii and Cochlodinium sp. of Matsuoka (1985a) both have brownpigmented cyst walls (Matsuoka,1985), as does Gymnodinium catenatum (Anderson et al., 1988).