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Omatidium
From Williams et al., 2017:
[Omatidium, Courtinat in Courtinat and Gaillard, 1980, p. 40; Emendation: Courtinat, 1989, p. 168, 170
Type species: originally as Hystrichodinium amphiacanthum, Cookson and Eisenack, 1958 (pl.5, fig.9)] ; Omatidium amphiacanthum, Courtinat, 1980
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Original description: [Courtinat, 1980]: (Translation: Stover and Williams, 1987, p. 167):
Description:
Cyst skolochorate, ovoidal to polygonal; paratabulation formula: ?`, ?a, 6", ?c, 5```, ?p., ?p.v, 1````. Parasutures indicated by the bases of ridges. Spines hollow, long, simple, inserted at the junctions [= meeting points] of the paraplates, situated only at the poles and in a plane. Archeopyle not observed.
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Modified description:
Stover and Williams, 1987, p. 167:
Synopsis:
Ovoidal to polygonal cysts with four or five long gonal spines at each pole; paratabulation indicated by low parasutural crests, complete formula unknown; archeopyle not observed.
Description:
Shape: Body ovoidal to polygonal.
Wall relationships: Unknown; probably two appressed wall layers except where spines are formed.
Wall features: Low, parasutural crests present; four or five long gonal spines at each pole.
Archeopyle: Not observed.
Paratabulation: Indicated by parasutural features; formula, insofar as known: ?`, 6", Xc, 5```,1````.
Paracingulum: Bordered by low, transverse crests and undivided.
Parasulcus: Elongate, straight, and extends the length of the body.
Size: Intermediate to large, length about 70 to 180 µm.
Affinities:
According to Courtinat in Courtinat and Gaillard (1980), Omatidium differs from Hystrichodinium Deflandre 1935 emended Clarke and Verdier 1967 in having fewer processes (gonal only), which are confined to the polar areas and whose tips are unbranched. Raphidodinium Deflandre 1936b emended Sarjeant and Downie 1982 has solid, very long processes whose lengths are greater than twice that of the body.
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Emended description:
Courtinat, 1989: (Translation: LPP):
Diagnosis:
Spiniferate chorate cyst, acavate (wall formed by an autophragm only), provided with very long, hollow, apicular processes (longer than half the smallest body dimension). The processes may be attached to low septa with smooth crests. The processes typically in gonal position, and the crests suggest a gonyaulacacean paratabulation. The sulcus, when observable, is type S.
The archaeopyle is type P(3``) following the Kofoid notation, and type P(4) following the Taylor-Evitt notation.
The epicyst bears a mamelon without processes. Two adcingular crests are present, and that developed on the hypocyst is more prominent than that of the epicyst. The postadcingular crest presents processes of which some are grouped in pairs.
Affinities:
The elements distinguishing Omatidium are a precingular archaeopyle (monoplacoid operculum) and very long gonal processes, which distinguished it from the following genera:
- Luehndea Morgenroth 1970: epicystal archaeopyle (tAtItP)
- Hystrichodinium Deflandre 1935: sutural processes (gonal and intergonal)
- Raphidodinium Deflandre 1936: restricted number of processes (9) and an unusual form of the hypocyst which suggests 2 antapical horns
- Cauca Davey and Verdier 1971: epicystal archaeopyle (tAtP)
- Xiphophoridium Sarjeant 1966: apical archaeopyle (tA)
The genus Omatidium shows a certain affinity with the genus Raphidodinium, if one just sticks to the criteria of (gonal) processes and archaeopyle type (P(3``))/(P(4)). However, these two forms are very dissimilar from one another in the number of processes. Although this is hypothetic, one may consider a phyletic relation between these different genera. The genus Luehndea appears, in this context, to be the earliest (Pliensbachian-Toarcian); It could constitute an initial form to the genera and species of Omatidium (O. amphiacanthum and O. bernieri), Hystrichodinium pulchrum Deflandre (known since the Kimmeridgian) and Hystrichodinium lanceolatum Davies (of which the archaeopyle type (4AP(3``)) would justify the creation of a new genus).
[Omatidium, Courtinat in Courtinat and Gaillard, 1980, p. 40; Emendation: Courtinat, 1989, p. 168, 170
Type species: originally as Hystrichodinium amphiacanthum, Cookson and Eisenack, 1958 (pl.5, fig.9)] ; Omatidium amphiacanthum, Courtinat, 1980
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Original description: [Courtinat, 1980]: (Translation: Stover and Williams, 1987, p. 167):
Description:
Cyst skolochorate, ovoidal to polygonal; paratabulation formula: ?`, ?a, 6", ?c, 5```, ?p., ?p.v, 1````. Parasutures indicated by the bases of ridges. Spines hollow, long, simple, inserted at the junctions [= meeting points] of the paraplates, situated only at the poles and in a plane. Archeopyle not observed.
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Modified description:
Stover and Williams, 1987, p. 167:
Synopsis:
Ovoidal to polygonal cysts with four or five long gonal spines at each pole; paratabulation indicated by low parasutural crests, complete formula unknown; archeopyle not observed.
Description:
Shape: Body ovoidal to polygonal.
Wall relationships: Unknown; probably two appressed wall layers except where spines are formed.
Wall features: Low, parasutural crests present; four or five long gonal spines at each pole.
Archeopyle: Not observed.
Paratabulation: Indicated by parasutural features; formula, insofar as known: ?`, 6", Xc, 5```,1````.
Paracingulum: Bordered by low, transverse crests and undivided.
Parasulcus: Elongate, straight, and extends the length of the body.
Size: Intermediate to large, length about 70 to 180 µm.
Affinities:
According to Courtinat in Courtinat and Gaillard (1980), Omatidium differs from Hystrichodinium Deflandre 1935 emended Clarke and Verdier 1967 in having fewer processes (gonal only), which are confined to the polar areas and whose tips are unbranched. Raphidodinium Deflandre 1936b emended Sarjeant and Downie 1982 has solid, very long processes whose lengths are greater than twice that of the body.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Emended description:
Courtinat, 1989: (Translation: LPP):
Diagnosis:
Spiniferate chorate cyst, acavate (wall formed by an autophragm only), provided with very long, hollow, apicular processes (longer than half the smallest body dimension). The processes may be attached to low septa with smooth crests. The processes typically in gonal position, and the crests suggest a gonyaulacacean paratabulation. The sulcus, when observable, is type S.
The archaeopyle is type P(3``) following the Kofoid notation, and type P(4) following the Taylor-Evitt notation.
The epicyst bears a mamelon without processes. Two adcingular crests are present, and that developed on the hypocyst is more prominent than that of the epicyst. The postadcingular crest presents processes of which some are grouped in pairs.
Affinities:
The elements distinguishing Omatidium are a precingular archaeopyle (monoplacoid operculum) and very long gonal processes, which distinguished it from the following genera:
- Luehndea Morgenroth 1970: epicystal archaeopyle (tAtItP)
- Hystrichodinium Deflandre 1935: sutural processes (gonal and intergonal)
- Raphidodinium Deflandre 1936: restricted number of processes (9) and an unusual form of the hypocyst which suggests 2 antapical horns
- Cauca Davey and Verdier 1971: epicystal archaeopyle (tAtP)
- Xiphophoridium Sarjeant 1966: apical archaeopyle (tA)
The genus Omatidium shows a certain affinity with the genus Raphidodinium, if one just sticks to the criteria of (gonal) processes and archaeopyle type (P(3``))/(P(4)). However, these two forms are very dissimilar from one another in the number of processes. Although this is hypothetic, one may consider a phyletic relation between these different genera. The genus Luehndea appears, in this context, to be the earliest (Pliensbachian-Toarcian); It could constitute an initial form to the genera and species of Omatidium (O. amphiacanthum and O. bernieri), Hystrichodinium pulchrum Deflandre (known since the Kimmeridgian) and Hystrichodinium lanceolatum Davies (of which the archaeopyle type (4AP(3``)) would justify the creation of a new genus).