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Fetchamium prolixispinosum
Fetchamium prolixispinosum , Pearce and Williams, 2018, p. 18-20
Junior synonym: 1966 Oligosphaeridium prolixispinosum Davey and Williams: 76–77, pl. 8, figs. 2–3.
Holotype: Oligosphaeridium prolixispinosum Davey and Williams, 1966, pl. 8, fig. 3; Pl. 1, Fig. 4.
Locus typicus: Fetcham Mill, Surrey, England
Stratum typicum: Cenomanian
Emended diagnosis: Pearce and Williams, 2018:
A species of Fetchamium, possessing an elongate central body. The wall is two-layered, composed of smooth endophragm and periphragm that
separate to form hollow processes, but which are appressed elsewhere.
The tabulation formula of 4′, 6′′, 0–4c, 6′′′, 1p, 1–3s (ps), 1′′′′ is defined by processes that are tubular and open distally, mesotabular, typically absent on the cingulum or missing from some plates, and terminate in a number of fine thread-like spines. Three processes are present at
the hypocyst, representing a quinqueform hypocystal plate arrangement.
The archaeopyle is apical, Type tA(1′−4′) and the operculum is detached.
Affinities/Comparison: Pearce and Williams, 2018:
Fetchamium prolixispinosum differs from Hystrichosphaeridium bowerbankii Davey and Williams, 1966 and Hystrichosphaeridium recurvatum (White, 1842) Lejeune-Carpentier, 1940 by typically lacking, or rarely possessing, an incomplete number of cingular processes, and
further from the latter by possessing an elongated rather than sub-spherical central body.
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Original description: Davey and Williams, 1966, p. 76:
The periphragm of the central body and of the processes is smooth. The processes are thin-walled and have a fairly broad base up to 8 µm, with characteristic basal wrinkles. There are noticeable circles beneath the processes where only endophragm is present. The processes are about 3 µm in width for most of their length tapering to 2 µm distally before giving rise to the filiform spines. The spines are extremely delicate, 5 to 8 in number, and up to 15 µm in length. The number of processes varies from 16 to 18, the variation probably due to the number of sulcal processes present. In all specimens there is an obvious apical archaeopyle. Surrounding the archaeopyle are 6 precingular processes, then a diastema before the postcingular processes are reached. This diastema marks the position of the cingulum. The processes on the hypotract are difficult to assign to any dinoflagellate tabulation. There is no obvious antapical process, in fact 3 antapical processes usually seem to be present. The reflected tabulation appears to be (4"), 6", 6""", 3"""" and 1-3s.
Dimensions: holotype: overall width 64 µm, diameter of central body 40 by 20 µm, length of processes 18-24 µm, number of processes 17. Range: Length of central body, 33-43 µm, width 20-29 µm, length of processes 18-29 µm.
Junior synonym: 1966 Oligosphaeridium prolixispinosum Davey and Williams: 76–77, pl. 8, figs. 2–3.
Holotype: Oligosphaeridium prolixispinosum Davey and Williams, 1966, pl. 8, fig. 3; Pl. 1, Fig. 4.
Locus typicus: Fetcham Mill, Surrey, England
Stratum typicum: Cenomanian
Emended diagnosis: Pearce and Williams, 2018:
A species of Fetchamium, possessing an elongate central body. The wall is two-layered, composed of smooth endophragm and periphragm that
separate to form hollow processes, but which are appressed elsewhere.
The tabulation formula of 4′, 6′′, 0–4c, 6′′′, 1p, 1–3s (ps), 1′′′′ is defined by processes that are tubular and open distally, mesotabular, typically absent on the cingulum or missing from some plates, and terminate in a number of fine thread-like spines. Three processes are present at
the hypocyst, representing a quinqueform hypocystal plate arrangement.
The archaeopyle is apical, Type tA(1′−4′) and the operculum is detached.
Affinities/Comparison: Pearce and Williams, 2018:
Fetchamium prolixispinosum differs from Hystrichosphaeridium bowerbankii Davey and Williams, 1966 and Hystrichosphaeridium recurvatum (White, 1842) Lejeune-Carpentier, 1940 by typically lacking, or rarely possessing, an incomplete number of cingular processes, and
further from the latter by possessing an elongated rather than sub-spherical central body.
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Original description: Davey and Williams, 1966, p. 76:
The periphragm of the central body and of the processes is smooth. The processes are thin-walled and have a fairly broad base up to 8 µm, with characteristic basal wrinkles. There are noticeable circles beneath the processes where only endophragm is present. The processes are about 3 µm in width for most of their length tapering to 2 µm distally before giving rise to the filiform spines. The spines are extremely delicate, 5 to 8 in number, and up to 15 µm in length. The number of processes varies from 16 to 18, the variation probably due to the number of sulcal processes present. In all specimens there is an obvious apical archaeopyle. Surrounding the archaeopyle are 6 precingular processes, then a diastema before the postcingular processes are reached. This diastema marks the position of the cingulum. The processes on the hypotract are difficult to assign to any dinoflagellate tabulation. There is no obvious antapical process, in fact 3 antapical processes usually seem to be present. The reflected tabulation appears to be (4"), 6", 6""", 3"""" and 1-3s.
Dimensions: holotype: overall width 64 µm, diameter of central body 40 by 20 µm, length of processes 18-24 µm, number of processes 17. Range: Length of central body, 33-43 µm, width 20-29 µm, length of processes 18-29 µm.