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Echinidinium
From Fensome et al., 2019:
Echinidinium, Zonneveld, 1997, p.325 ex Head et al., 2001, p.633.
This name was not validly published in Zonneveld (1997) since that author did not provide a Latin diagnosis; such a diagnosis is required since the type is from a sediment trap and thus must be considered modern and not fossil.
Type: Zonneveld, 1997, pl.2, figs.1–4, as Echinidinium granulatum.
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Original description: [Zonneveld, 1997]:
Diagnosis:
Spheroidal, pigmented cysts covered with numerous randomly dispersed spines which are more or less similar in shape and length or are of two different types. Spines may be pigmented or transparent, smooth or striated and may be solid or hollow. Cyst wall is formed by a smooth pedium with a luxuria forming the processes. Archeopyle is chasmic formed by rupture along predetermined episomal sutures. Cyst wall may be smooth or ornamented.
Discussion:
Spheroidal pigmented cysts, covered with randomly dispersed spines are known to be produced generally by species of the Family Congruentidiaceae. The archeopyle of these species may either consist of the loss of one or more paraplates or is chasmic. The latter are known to be formed by Diplopelta parva (Abe) Matsuoka, 1988 (Matsuoka, 1988), Diplopelta symmetrica Pavillard, 1913 (Dale et al., 1993), Protoperidinium minutum (Kofoid) Loeblich, 1969 (Wall and Dale, 1968; Fukuyo et al., 1977) and Protoperidinium monospinum (Paulsen) Zonneveld et Dale, 1994 (Zonneveld and Dale, 1994). Modern and fossil cysts are known which closely resemble the cysts described above, in cyst outline, colour, archeopyle type and the presence of spines. However, (fossil) cysts which open by a single split and show no morphological evidence of dinoflagellate affinity, are generally assigned to the Acritarcha Evitt, 1963. Since recent hatching experiments clearly demonstrated the dinophycean character of several of these cysts, the new dinoflagellate cyst genus Echinidinium is erected to distinguish these forms from those of unknown affinity.
Affinities:
Echinidinium most closely resembles Algidasphaeridium in having randomly dispersed spines and a chasmic archeopyle. However, Algidasphaeridium has a granulate periphragm and endophragm, and small solid spines of similar lengths, whereas Echinidinium has a smooth pedium with a luxuria forming the ornamentations and solid or hollow spines that may have different lengths. Furthermore, Echinidinium is pigmented whereas the type species of Algidasphaeridium is transparent. Matsuoka and Bujak (1988) assigned Algidasphaeridium to the Gymnodiniaceae, because of its resemblance with the modern cysts of Pheopolykrikos hartmannii (Zimmermann) Matsuoka et Fukuyo, 1986, Cochlodinium sp. Matsuoka, 1985 and Gymnodinium catenatum Graham, 1943. As discussed above, incubation experiments suggest the thecal affinity of Echinidinium to be congruentidiacean. Echinidinium differs from all other genera in being spheroidal, pigmented, possessing a chasmic archeopyle and randomly dispersed spines.
Echinidinium, Zonneveld, 1997, p.325 ex Head et al., 2001, p.633.
This name was not validly published in Zonneveld (1997) since that author did not provide a Latin diagnosis; such a diagnosis is required since the type is from a sediment trap and thus must be considered modern and not fossil.
Type: Zonneveld, 1997, pl.2, figs.1–4, as Echinidinium granulatum.
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Zonneveld, 1997]:
Diagnosis:
Spheroidal, pigmented cysts covered with numerous randomly dispersed spines which are more or less similar in shape and length or are of two different types. Spines may be pigmented or transparent, smooth or striated and may be solid or hollow. Cyst wall is formed by a smooth pedium with a luxuria forming the processes. Archeopyle is chasmic formed by rupture along predetermined episomal sutures. Cyst wall may be smooth or ornamented.
Discussion:
Spheroidal pigmented cysts, covered with randomly dispersed spines are known to be produced generally by species of the Family Congruentidiaceae. The archeopyle of these species may either consist of the loss of one or more paraplates or is chasmic. The latter are known to be formed by Diplopelta parva (Abe) Matsuoka, 1988 (Matsuoka, 1988), Diplopelta symmetrica Pavillard, 1913 (Dale et al., 1993), Protoperidinium minutum (Kofoid) Loeblich, 1969 (Wall and Dale, 1968; Fukuyo et al., 1977) and Protoperidinium monospinum (Paulsen) Zonneveld et Dale, 1994 (Zonneveld and Dale, 1994). Modern and fossil cysts are known which closely resemble the cysts described above, in cyst outline, colour, archeopyle type and the presence of spines. However, (fossil) cysts which open by a single split and show no morphological evidence of dinoflagellate affinity, are generally assigned to the Acritarcha Evitt, 1963. Since recent hatching experiments clearly demonstrated the dinophycean character of several of these cysts, the new dinoflagellate cyst genus Echinidinium is erected to distinguish these forms from those of unknown affinity.
Affinities:
Echinidinium most closely resembles Algidasphaeridium in having randomly dispersed spines and a chasmic archeopyle. However, Algidasphaeridium has a granulate periphragm and endophragm, and small solid spines of similar lengths, whereas Echinidinium has a smooth pedium with a luxuria forming the ornamentations and solid or hollow spines that may have different lengths. Furthermore, Echinidinium is pigmented whereas the type species of Algidasphaeridium is transparent. Matsuoka and Bujak (1988) assigned Algidasphaeridium to the Gymnodiniaceae, because of its resemblance with the modern cysts of Pheopolykrikos hartmannii (Zimmermann) Matsuoka et Fukuyo, 1986, Cochlodinium sp. Matsuoka, 1985 and Gymnodinium catenatum Graham, 1943. As discussed above, incubation experiments suggest the thecal affinity of Echinidinium to be congruentidiacean. Echinidinium differs from all other genera in being spheroidal, pigmented, possessing a chasmic archeopyle and randomly dispersed spines.