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Fetchamium
Fetchamium, Pearce and Williams, 2018, p. 18
Type species: Oligosphaeridium prolixispinosum, Davey and Williams, 1966 (pl. 8, fig. 3; Pl. 1 fig. 4.)
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Original description: [Pearce and Williams, 2018]:
Diagnosis:
Goniodomacean dinoflagellate cysts, possessing an apical archaeopyle and hollow, tubular, mesotabular processes that reflect a quinqueform tabulation. Cingular processes are absent or occasionally present but do not form a complete set and sulcal processes do not exceed four
(including the posterior sulcal).
Description:
Goniodomacean chorate dinoflagellate cysts with a two-layered wall, composed of endophragm and periphragm that are detached where the periphragm forms the hollow processes, but which are appressed elsewhere.
Processes are tubular and open distally, are mesotabular, and may be absent on the cingulum or be represented by an incomplete number (i.e. less than six). There can be one to four sulcal processes (including the posterior sulcal). Three processes are present at the antapex, representing a quinqueform hypocystal plate arrangement.
The Archaeopyle is apical, Type tA(1′−4′) and the operculum is detached.
Remarks:
Hystrichosphaeridium is placed in the subfamily Pyrodinioideae; however, this must be considered questionable since the basis Fensome et al. (1993) used to justify inclusion of Hystrichosphaeridium in that subfamily (based on a drawing in Evitt, 1985) may be incorrect. Evitt’s
drawing was labelled Hystrichosphaeridium cf. H. tubiferum but described as having processes that merge “distally into a clearly polygonal unit of irregularly perforate ectophragm that extends without interruption over the process cavity”. The processes in Hystrichosphaeridium are open distally and lack an ectophragm.
Affinities/Comparison:
Fetchamium differs from other pyrodinioideans, Hystrichosphaeridium and Tanyosphaeridium in lacking cingular processes or, if rarely present, by possessing a variable but incomplete number. Homotryblium and Polysphaeridium differ by possessing an epicystal archaeopyle. The leptodinioidean Oligosphaeridium differs in being sexiform.
Type species: Oligosphaeridium prolixispinosum, Davey and Williams, 1966 (pl. 8, fig. 3; Pl. 1 fig. 4.)
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Original description: [Pearce and Williams, 2018]:
Diagnosis:
Goniodomacean dinoflagellate cysts, possessing an apical archaeopyle and hollow, tubular, mesotabular processes that reflect a quinqueform tabulation. Cingular processes are absent or occasionally present but do not form a complete set and sulcal processes do not exceed four
(including the posterior sulcal).
Description:
Goniodomacean chorate dinoflagellate cysts with a two-layered wall, composed of endophragm and periphragm that are detached where the periphragm forms the hollow processes, but which are appressed elsewhere.
Processes are tubular and open distally, are mesotabular, and may be absent on the cingulum or be represented by an incomplete number (i.e. less than six). There can be one to four sulcal processes (including the posterior sulcal). Three processes are present at the antapex, representing a quinqueform hypocystal plate arrangement.
The Archaeopyle is apical, Type tA(1′−4′) and the operculum is detached.
Remarks:
Hystrichosphaeridium is placed in the subfamily Pyrodinioideae; however, this must be considered questionable since the basis Fensome et al. (1993) used to justify inclusion of Hystrichosphaeridium in that subfamily (based on a drawing in Evitt, 1985) may be incorrect. Evitt’s
drawing was labelled Hystrichosphaeridium cf. H. tubiferum but described as having processes that merge “distally into a clearly polygonal unit of irregularly perforate ectophragm that extends without interruption over the process cavity”. The processes in Hystrichosphaeridium are open distally and lack an ectophragm.
Affinities/Comparison:
Fetchamium differs from other pyrodinioideans, Hystrichosphaeridium and Tanyosphaeridium in lacking cingular processes or, if rarely present, by possessing a variable but incomplete number. Homotryblium and Polysphaeridium differ by possessing an epicystal archaeopyle. The leptodinioidean Oligosphaeridium differs in being sexiform.