Back
Echinidinium aculeatum
Echinidinium aculeatum Zonneveld, 1997, p.328-329, pl.3, figs.1-5; text-figs.5A-B.
Name not validly published: no Latin description provided.
Holotype: Zonneveld, 1997, pl.3, figs.1-3. The holotype is from a sediment trap and does not have a stratigraphic context; hence it must be treated as an extant form rather than a fossil, its name requiring a Latin diagnosis for validation (Head, 2003a, p.171-172).
Age: Holocene.
(Zonneveld, 1997):
Holotype: MST-8-B62, England finder co-ordinate (EFC) 043 (Plate III, 1-3).
Repository: Collection of Fachbereich-5 Geowissenschaften, Universität Bremen, Germany.
Type locality: Offshore Somalia, Arabian Sea.
Etymology: With reference to its aculeate spine tips.
Diagnosis: Spheroidal cysts covered with randomly distributed spines. Cyst wall pigmented with a thin smooth pedium. The hollow, smooth spines are formed by separation of the luxuria and the pedium. Between the processes a luxuria of isolated granulae can be present. Spines are tapering towards their distal ends, with open aculeate distal tips that have two to four distal extremities. Spine bases are (sub) sphaerical. The chasmic archeopyle consists of a split along a single suture. No other paratabulation is reflected.
Additional remarks: The cysts have a thin wall which is slightly pigmented. When a luxuria is present between the spines, it is very thin with small granulae (Fig. 5B, a). Cysts have less than 50 spines. Because of the rigid character of the spines and the thin cyst wall, the cysts are often folded. Length of the spines is about 30% of the cyst body (Fig. 5A). No variation in the relative height of spines is detected. The spines are generally rigid but may be curved, Their aculeate ends have two to four distal extremities (Fig. 5C). Some specimens have been observed were these distal extremities are bifurcate. The archeopyle is rarely observed.
Dimensions: Holotype: body diameter 25.3 µm; spine length 7.4 µm; diameter spines 2.1 µm. Range: body diameter 16-26 µm (mean 20 µm, n = 14); spine length 6-8 µm (mean 7 µm, n = 14); diameter spines 1.5 2.5 µm (mean 2 µm, n = 14).
Comparison with other taxa: Echinidinium aculeatum most closely resembles cysts formed by Diplopelta parva (Abe) Matsuoka, 1988 (Matsuoka, 1988). However, E. aculeatum is a smaller cyst (diameter D. parva=38-45 pro) and has tapering spines with open aculeate distal ends in contrast to D. parva which has closed acuminate spines. Furthermore, the chasmic archeopyle of D. parva consist of a split along one long and four short sides whereas the archeopyle of E. aculeaturn consist of a split along a single suture only (Plate III, 1). E. aculeatum differs from all other Echinidinium species, cysts of Protoperidinium minutum (Kofoid) Loeblich, 1969 as described by Wall and Dale (1968) and Fukuyo et al. (1977), cysts of Diplopelta symmetrica Pavillard, 1913, Protoperidinium monospinum (Paulsen) Zonneveld et Dale, 1994, Algidasphaeridium? minutum (Harland et Reid) Matsuoka et Bujak, 1988 and Pheopolykrikos hartmannii (Zimmermann) Matsuoka et Fukuyo, 1986 in having tapering spines with open, aculeate distal tips and having an archeopyle formed by a split along a single suture only.
Stratigraphic range: Late Pleistocene-Recent (Zonneveld, 1996b; Zonneveld et al., 1996a)
Environmental affinity: E. aculeatum can be observed in the surface sediment samples of the Arabian Sea with the exception of the central part of the basin (Zonneveld, 1996a,b). The highest abundances are found in the Somali upwelling region and the Oman-Pakistan coastal region. E. aculeatum is also observed in Late Quaternary sediments of the Madeira Abyssal Plain f-turbidite that are thought to originate from the continental margin of northwestern Africa (Weaver et al., 1992; Zonneveld et al., 1996b) and surface sediments of the Benguela upwelling region (R. Hock, pers. commun.).
Name not validly published: no Latin description provided.
Holotype: Zonneveld, 1997, pl.3, figs.1-3. The holotype is from a sediment trap and does not have a stratigraphic context; hence it must be treated as an extant form rather than a fossil, its name requiring a Latin diagnosis for validation (Head, 2003a, p.171-172).
Age: Holocene.
(Zonneveld, 1997):
Holotype: MST-8-B62, England finder co-ordinate (EFC) 043 (Plate III, 1-3).
Repository: Collection of Fachbereich-5 Geowissenschaften, Universität Bremen, Germany.
Type locality: Offshore Somalia, Arabian Sea.
Etymology: With reference to its aculeate spine tips.
Diagnosis: Spheroidal cysts covered with randomly distributed spines. Cyst wall pigmented with a thin smooth pedium. The hollow, smooth spines are formed by separation of the luxuria and the pedium. Between the processes a luxuria of isolated granulae can be present. Spines are tapering towards their distal ends, with open aculeate distal tips that have two to four distal extremities. Spine bases are (sub) sphaerical. The chasmic archeopyle consists of a split along a single suture. No other paratabulation is reflected.
Additional remarks: The cysts have a thin wall which is slightly pigmented. When a luxuria is present between the spines, it is very thin with small granulae (Fig. 5B, a). Cysts have less than 50 spines. Because of the rigid character of the spines and the thin cyst wall, the cysts are often folded. Length of the spines is about 30% of the cyst body (Fig. 5A). No variation in the relative height of spines is detected. The spines are generally rigid but may be curved, Their aculeate ends have two to four distal extremities (Fig. 5C). Some specimens have been observed were these distal extremities are bifurcate. The archeopyle is rarely observed.
Dimensions: Holotype: body diameter 25.3 µm; spine length 7.4 µm; diameter spines 2.1 µm. Range: body diameter 16-26 µm (mean 20 µm, n = 14); spine length 6-8 µm (mean 7 µm, n = 14); diameter spines 1.5 2.5 µm (mean 2 µm, n = 14).
Comparison with other taxa: Echinidinium aculeatum most closely resembles cysts formed by Diplopelta parva (Abe) Matsuoka, 1988 (Matsuoka, 1988). However, E. aculeatum is a smaller cyst (diameter D. parva=38-45 pro) and has tapering spines with open aculeate distal ends in contrast to D. parva which has closed acuminate spines. Furthermore, the chasmic archeopyle of D. parva consist of a split along one long and four short sides whereas the archeopyle of E. aculeaturn consist of a split along a single suture only (Plate III, 1). E. aculeatum differs from all other Echinidinium species, cysts of Protoperidinium minutum (Kofoid) Loeblich, 1969 as described by Wall and Dale (1968) and Fukuyo et al. (1977), cysts of Diplopelta symmetrica Pavillard, 1913, Protoperidinium monospinum (Paulsen) Zonneveld et Dale, 1994, Algidasphaeridium? minutum (Harland et Reid) Matsuoka et Bujak, 1988 and Pheopolykrikos hartmannii (Zimmermann) Matsuoka et Fukuyo, 1986 in having tapering spines with open, aculeate distal tips and having an archeopyle formed by a split along a single suture only.
Stratigraphic range: Late Pleistocene-Recent (Zonneveld, 1996b; Zonneveld et al., 1996a)
Environmental affinity: E. aculeatum can be observed in the surface sediment samples of the Arabian Sea with the exception of the central part of the basin (Zonneveld, 1996a,b). The highest abundances are found in the Somali upwelling region and the Oman-Pakistan coastal region. E. aculeatum is also observed in Late Quaternary sediments of the Madeira Abyssal Plain f-turbidite that are thought to originate from the continental margin of northwestern Africa (Weaver et al., 1992; Zonneveld et al., 1996b) and surface sediments of the Benguela upwelling region (R. Hock, pers. commun.).