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Xenascus spinatus
Xenascus spinatus Prince et al., 2008, p.91, pl.2, figs.4–7.
Holotype: Prince et al., 2008, pl.2, figs.4–5.
Age: late Santonian.
Original description (Prince et al., 2008)
Holotype: Slide PRC 3972, WCI 124, E/F ref. R43.
Paratype: Slide PRC 1508, WTN 17, E/F ref. M27 (from White Ness, east Kent).
Repository: Institute of Geography and Earth Sciences, University of Wales, Aberystwyth, Wales, UK.
Type locality: Whitecliff, Isle of Wight, England.
Stratigraphic horizon: Upper Santonian, top U. socialis Zone.
Etymology: Spinatus — with reference to the small spines.
Diagnosis: A species of Xenascus with the wall layers widely separated, usually from the top of the lateral horn around to just under the paracingulum. The outer wall layer is covered with many spines of various shapes up to 6–8 µm in length.
Description: Inner body round to oval, relatively thick with a fine reticulate ornament. A variable degree of paratabulation may be observed expressed as ridges with stout processes arising from either the gonals or from the intratabular area.
The thinner outer body forms the processes, the lateral horn and the antapical horns. The outer body is separated from the inner body, usually from the top of the lateral horn, around the antapical horn to just under the paracingulum on the opposite side. Occasionally, the wall layers are separated from the archaeopyle round to the archaeopyle on the opposite side. The lateral horn which is up to approximately 64 µm long is dagger-like and gently curved in shape. The antapical horn, which is usually well developed, is either broadly triangular in shape or more broad and rounded.
The distinguishing feature of this form is the presence of many small spines of variable morphology on the outer body, in addition to those spines/processes normally seen on species of Xenascus. These spines are up to 6–8 µm in length and may be capitate, minutely bifid or fairly thick and expanding slightly, giving the cyst an irregular to denticulate edge. The spines on the antapical horn are arranged in rows passing up the horn.
Dimensions: Holotype: central body 48 µm wide × 61 µm long; overall (excluding processes) 66 µm wide × 130 µm long; maximum process length 12 µm. Range of 25 measured specimens: central body 34–66 µm (average 52 µm) wide × 26–60 µm (average 46 µm) long; overall (excluding processes) 48–94 µm (average 69 µm) wide × 56–130 µm (average 94 µm) long; maximum process length 33 µm.
Comparison: Differs from all other Xenascus species by the widely separated wall layers, the outer of which has many small spines of variable morphology. Xenascus gochtii, X. perforatus and X. yunii ( Plate II, 8, 9) are similar in terms of wall separation but all lack the small spines.
Holotype: Prince et al., 2008, pl.2, figs.4–5.
Age: late Santonian.
Original description (Prince et al., 2008)
Holotype: Slide PRC 3972, WCI 124, E/F ref. R43.
Paratype: Slide PRC 1508, WTN 17, E/F ref. M27 (from White Ness, east Kent).
Repository: Institute of Geography and Earth Sciences, University of Wales, Aberystwyth, Wales, UK.
Type locality: Whitecliff, Isle of Wight, England.
Stratigraphic horizon: Upper Santonian, top U. socialis Zone.
Etymology: Spinatus — with reference to the small spines.
Diagnosis: A species of Xenascus with the wall layers widely separated, usually from the top of the lateral horn around to just under the paracingulum. The outer wall layer is covered with many spines of various shapes up to 6–8 µm in length.
Description: Inner body round to oval, relatively thick with a fine reticulate ornament. A variable degree of paratabulation may be observed expressed as ridges with stout processes arising from either the gonals or from the intratabular area.
The thinner outer body forms the processes, the lateral horn and the antapical horns. The outer body is separated from the inner body, usually from the top of the lateral horn, around the antapical horn to just under the paracingulum on the opposite side. Occasionally, the wall layers are separated from the archaeopyle round to the archaeopyle on the opposite side. The lateral horn which is up to approximately 64 µm long is dagger-like and gently curved in shape. The antapical horn, which is usually well developed, is either broadly triangular in shape or more broad and rounded.
The distinguishing feature of this form is the presence of many small spines of variable morphology on the outer body, in addition to those spines/processes normally seen on species of Xenascus. These spines are up to 6–8 µm in length and may be capitate, minutely bifid or fairly thick and expanding slightly, giving the cyst an irregular to denticulate edge. The spines on the antapical horn are arranged in rows passing up the horn.
Dimensions: Holotype: central body 48 µm wide × 61 µm long; overall (excluding processes) 66 µm wide × 130 µm long; maximum process length 12 µm. Range of 25 measured specimens: central body 34–66 µm (average 52 µm) wide × 26–60 µm (average 46 µm) long; overall (excluding processes) 48–94 µm (average 69 µm) wide × 56–130 µm (average 94 µm) long; maximum process length 33 µm.
Comparison: Differs from all other Xenascus species by the widely separated wall layers, the outer of which has many small spines of variable morphology. Xenascus gochtii, X. perforatus and X. yunii ( Plate II, 8, 9) are similar in terms of wall separation but all lack the small spines.