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Echinidinium euaxum
Echinidinium euaxum (Head, 1993, p.24,26, fig.16, nos.1-8,11; fig.26, no.4) Head et al., 2001, p.631.
Originally Algidasphaeridium?, subsequently (and now) Echinidinium.
This combination was not validly published in Zonneveld (1997, p334) since the generic name was not validated until 2001.
Holotype: Head, 1993, fig.16, no.11.
Age: latest Pliocene.
(Head, 1993):
Multispinula cf. M. minuta auct. non Harland and Reid in Harland et al., 1980. DUFFIELD AND STEIN, 1986, p. 34, P1. 1, fig. 7.
Multispinula sp. LENOIR AND HART, 1986, P1. 4, fig. 1.
Multispinula spp. ?BINT, 1988, p. 333, fig. 4B.
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 2.0 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. Twenty-four specimens were measured.
Remarks. -Unbroken process terminations were observed only in lateral view. They are probably small platforms but might be minutely bifid. Assignment to Algidasphaeridium is provisional because A.? euaxum n. sp. has hollow processes and is pigmented, unlike the type species A. capillatum.
Etymology. -Greek, Euaxos, brittle, easily broken; with respect to the frequent breakage of processes on this species.
Holotype.-Sample DPX 325-345, slide 3; R51/3. Figure 16.11. Royal Ontario Museum catalog number ROM49416.
Repository. -Department of Invertebrate Palaeontology, Royal Ontario Museum, Toronto, Ontario.
Comparison. -Multispinula cf. M. minuta of Duffield and Stein (1986) and Multispinula sp. of LeNoir and Hart (1986) are considered conspecific with A.? euaxum n. sp. 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 n. sp. The processes are rather small but this specimen is part of a plexus of morphologies (as Multispinula spp., in Bint, 1988, p. 333). 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 n. sp. Algidasphaeridium capillatum Matsuoka and Bujak, 1988, described from upper Miocene deposits of the Bering Sea, differs from A. euaxum n. sp. 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 modem 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, 1985a), as does Gymnodinium catenatum (Anderson et al., 1988).
Previous records. -This species was recorded from lower through upper Miocene (planktonic foraminiferal zones N5 through N17) deposits of the Gulf of Mexico by Duffield and Stein (1986, as Multispinula cf. M. minuta), and from upper lower Miocene deposits, also of the Gulf of Mexico, by LeNoir and Hart (1986, as Multispinula sp.). It possibly occurs in Recent sediments of northwestern Australia (as Multispinula spp. in Bint, 1988, fig. 4B).
Stratigraphic range. -Lower Miocene of the Gulf of Mexico (Duffield and Stein, 1986) through uppermost Pliocene of the St. Erth Beds (this study) and possibly Recent of Australia (Bint, 1988).
Paleoecology. -Algidasphaeridium? euaxum n. sp. is tentatively inferred to be a warm-water species mainly of inner neritic environments, based on its occurrence in the St. Erth Beds (this study) and near-delta shelf of the Gulf of Mexico (Duffield and Stein, 1986). Its possible occurrence in Recent sediments of subtropical, inner neritic northwestern Australia (Bint, 1988) is consistent with this interpretation.
Originally Algidasphaeridium?, subsequently (and now) Echinidinium.
This combination was not validly published in Zonneveld (1997, p334) since the generic name was not validated until 2001.
Holotype: Head, 1993, fig.16, no.11.
Age: latest Pliocene.
(Head, 1993):
Multispinula cf. M. minuta auct. non Harland and Reid in Harland et al., 1980. DUFFIELD AND STEIN, 1986, p. 34, P1. 1, fig. 7.
Multispinula sp. LENOIR AND HART, 1986, P1. 4, fig. 1.
Multispinula spp. ?BINT, 1988, p. 333, fig. 4B.
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 2.0 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. Twenty-four specimens were measured.
Remarks. -Unbroken process terminations were observed only in lateral view. They are probably small platforms but might be minutely bifid. Assignment to Algidasphaeridium is provisional because A.? euaxum n. sp. has hollow processes and is pigmented, unlike the type species A. capillatum.
Etymology. -Greek, Euaxos, brittle, easily broken; with respect to the frequent breakage of processes on this species.
Holotype.-Sample DPX 325-345, slide 3; R51/3. Figure 16.11. Royal Ontario Museum catalog number ROM49416.
Repository. -Department of Invertebrate Palaeontology, Royal Ontario Museum, Toronto, Ontario.
Comparison. -Multispinula cf. M. minuta of Duffield and Stein (1986) and Multispinula sp. of LeNoir and Hart (1986) are considered conspecific with A.? euaxum n. sp. 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 n. sp. The processes are rather small but this specimen is part of a plexus of morphologies (as Multispinula spp., in Bint, 1988, p. 333). 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 n. sp. Algidasphaeridium capillatum Matsuoka and Bujak, 1988, described from upper Miocene deposits of the Bering Sea, differs from A. euaxum n. sp. 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 modem 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, 1985a), as does Gymnodinium catenatum (Anderson et al., 1988).
Previous records. -This species was recorded from lower through upper Miocene (planktonic foraminiferal zones N5 through N17) deposits of the Gulf of Mexico by Duffield and Stein (1986, as Multispinula cf. M. minuta), and from upper lower Miocene deposits, also of the Gulf of Mexico, by LeNoir and Hart (1986, as Multispinula sp.). It possibly occurs in Recent sediments of northwestern Australia (as Multispinula spp. in Bint, 1988, fig. 4B).
Stratigraphic range. -Lower Miocene of the Gulf of Mexico (Duffield and Stein, 1986) through uppermost Pliocene of the St. Erth Beds (this study) and possibly Recent of Australia (Bint, 1988).
Paleoecology. -Algidasphaeridium? euaxum n. sp. is tentatively inferred to be a warm-water species mainly of inner neritic environments, based on its occurrence in the St. Erth Beds (this study) and near-delta shelf of the Gulf of Mexico (Duffield and Stein, 1986). Its possible occurrence in Recent sediments of subtropical, inner neritic northwestern Australia (Bint, 1988) is consistent with this interpretation.