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Wetzeliella quinquelata
Wetzeliella quinquelatum (Williams and Downie, 1966b, p.191–192, pl.18, fig.7) Costa and Downie, 1979, p.43.
Originally Wetzeliella homomorpha var. quinquelata, subsequently Wetzeliella homomorpha subsp. quinquelata, thirdly Apectodinium homomorphum subsp. quinquelatum, fourthly Wetzeliella quinquelata, fifthly (and now) Apectodinium quinquelatum.
Taxonomic senior synonym (at specific rank): Hystrichosphaeridium (now Apectodinium) geometricum, by implication in Harland (1979c, p.67), who considered the latter to be the junior name — however, Lentin and Williams (1989, p.18) retained Apectodinium quinquelatum.
Holotype: Williams and Downie, 1966b, pl.18, fig.7.
Age: early Eocene
Original description: Williams and Downie, 1966, p. 191-192: Wetzeliella (Wetzeliella) homomorpha var. quinquelata
This is a variety of W. homomorpha having a thin periphragm with a distinctly pentagonal outline. Each angle of the periphragm may be marked by a branched process, larger than the rest, or by a horn not exceeding 20 Ám in length.
When two antapical horns are present, the right is invariably the longer. The enclosed capsule has a pentagonal outline and is closely pressed against the periphragm save at the angles. The capsule wall is usually thin and smooth.
The tabulation is often well shown from the orientation of the processes, which in some specimens are almost restricted to the plate boundary zone in simulate complexes, whilst in others they are more numerous and irregularly arranged. The hollow, simple or branched processes tend to be concentrated on the ambitus of the periphragm. As in the typical W. Homomorpha, the processes show considerable variation distally. They are rlearly always closed with acuminate, blunt or bifid tips, but several specimens with processes that open distally with aculeate or entire margins are included since they are identical to W. homomorpha var. quinquelata in outline, wall thickness and tendency for processes to be concentrated on the ambitus. As is to be expected, intermediate forms exist between W. homomorpha and W. homomorpha var. quinquelata.
Dimensions: holotype: periphragm, length 94 µm; breadth 105 µm. Capsule, length 69 µm; breadth 69 µm. Observed range: outer shell, length (including horns and processes) 73-94 µm, length (excluding horns and processes) 50-72 µm, breadth (including horns and processes) 77-105 µm, breadth (excluding horns and processes) 53-70 µm. Capsule, length 47-69 µm; breadth 50-69 µm.
Affinities:
Williams and Downie, 1966, p. 192: Wetzeliella (Wetzeliella) homomorpha var. quinquelata
Pastiels (1948) stated that H. geometricum is represented by flattened capsules, roughly pentagonal, of which one of the sides, sometimes concave, is smaller. Unfortunately the name created by Pastiels was pre-occupied by Hystrichosphaeridium geometricum Deflandre 1942, for forms with a polygonal test from the Palaeozoic (since transferred to Veryhacium). This was pointed out by Deflandre & Cookson (1955), who in erecting W. homomorpha compared it to H. geometricum (Pastiels) and corlcluded that the two were probably synonymous. However, in the diagnosis of W. homomorpha, Deflandre & Cookson stated that the theca is polygonal, more or less rounded. A detailed study of London Clay forms attributable to the W. homomorpha-H. geometricum (Pastiels) complex has shown that there are two extreme forms of common occurrence, firstly pentagonal forms, often with well developed horns, and secondly ovoidal, sub-spherical or rhomboidal forms lacking horns. The two forms can be readily separated, although intermediate types do occur. Pastiels figured, as within his species, types identical to the two extreme London Clay forms, as well as intermediate specimens, although the holotype of H. geometricum (Pastiels) is almost pentagonal and the accompanying description suggests that specimens with a pentagonal outline were the more frequent in the Ypresian. It therefore seems advisable to restrict W. homomorpha to the forms having sub-spherical, ovoidal or rhomboidal outline, whilst defining a variety, W. homomorpha var. quinquelata, to include forms having a pericoel with pentagonal outline with or without horns. This is a workable system in the London Clay and avoids too much infraspecific variation going unheeded..
Originally Wetzeliella homomorpha var. quinquelata, subsequently Wetzeliella homomorpha subsp. quinquelata, thirdly Apectodinium homomorphum subsp. quinquelatum, fourthly Wetzeliella quinquelata, fifthly (and now) Apectodinium quinquelatum.
Taxonomic senior synonym (at specific rank): Hystrichosphaeridium (now Apectodinium) geometricum, by implication in Harland (1979c, p.67), who considered the latter to be the junior name — however, Lentin and Williams (1989, p.18) retained Apectodinium quinquelatum.
Holotype: Williams and Downie, 1966b, pl.18, fig.7.
Age: early Eocene
Original description: Williams and Downie, 1966, p. 191-192: Wetzeliella (Wetzeliella) homomorpha var. quinquelata
This is a variety of W. homomorpha having a thin periphragm with a distinctly pentagonal outline. Each angle of the periphragm may be marked by a branched process, larger than the rest, or by a horn not exceeding 20 Ám in length.
When two antapical horns are present, the right is invariably the longer. The enclosed capsule has a pentagonal outline and is closely pressed against the periphragm save at the angles. The capsule wall is usually thin and smooth.
The tabulation is often well shown from the orientation of the processes, which in some specimens are almost restricted to the plate boundary zone in simulate complexes, whilst in others they are more numerous and irregularly arranged. The hollow, simple or branched processes tend to be concentrated on the ambitus of the periphragm. As in the typical W. Homomorpha, the processes show considerable variation distally. They are rlearly always closed with acuminate, blunt or bifid tips, but several specimens with processes that open distally with aculeate or entire margins are included since they are identical to W. homomorpha var. quinquelata in outline, wall thickness and tendency for processes to be concentrated on the ambitus. As is to be expected, intermediate forms exist between W. homomorpha and W. homomorpha var. quinquelata.
Dimensions: holotype: periphragm, length 94 µm; breadth 105 µm. Capsule, length 69 µm; breadth 69 µm. Observed range: outer shell, length (including horns and processes) 73-94 µm, length (excluding horns and processes) 50-72 µm, breadth (including horns and processes) 77-105 µm, breadth (excluding horns and processes) 53-70 µm. Capsule, length 47-69 µm; breadth 50-69 µm.
Affinities:
Williams and Downie, 1966, p. 192: Wetzeliella (Wetzeliella) homomorpha var. quinquelata
Pastiels (1948) stated that H. geometricum is represented by flattened capsules, roughly pentagonal, of which one of the sides, sometimes concave, is smaller. Unfortunately the name created by Pastiels was pre-occupied by Hystrichosphaeridium geometricum Deflandre 1942, for forms with a polygonal test from the Palaeozoic (since transferred to Veryhacium). This was pointed out by Deflandre & Cookson (1955), who in erecting W. homomorpha compared it to H. geometricum (Pastiels) and corlcluded that the two were probably synonymous. However, in the diagnosis of W. homomorpha, Deflandre & Cookson stated that the theca is polygonal, more or less rounded. A detailed study of London Clay forms attributable to the W. homomorpha-H. geometricum (Pastiels) complex has shown that there are two extreme forms of common occurrence, firstly pentagonal forms, often with well developed horns, and secondly ovoidal, sub-spherical or rhomboidal forms lacking horns. The two forms can be readily separated, although intermediate types do occur. Pastiels figured, as within his species, types identical to the two extreme London Clay forms, as well as intermediate specimens, although the holotype of H. geometricum (Pastiels) is almost pentagonal and the accompanying description suggests that specimens with a pentagonal outline were the more frequent in the Ypresian. It therefore seems advisable to restrict W. homomorpha to the forms having sub-spherical, ovoidal or rhomboidal outline, whilst defining a variety, W. homomorpha var. quinquelata, to include forms having a pericoel with pentagonal outline with or without horns. This is a workable system in the London Clay and avoids too much infraspecific variation going unheeded..