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Cousteaudinium
From Williams et al., 2017:
[Cousteaudinium, de Verteuil and Norris, 1996a, p. 109, 111
Type species: Cousteaudinium aubryae, de Verteuil and Norris, 1996a (pl.1, figs.1–3,6,9)]
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Original description: [de Verteuil and Norris, 1996]:
Diagnosis:
Circumcavate and variably chorate gonyaulacacean cysts lacking cingular processes and having an apical archeopyle; tabulation otherwise variably expressed by intratabular processes, usually one per field; fields in the sulcal and posterior ventral area with or without processes.
Original description:
The wall comprises the pedium, with or without proximate luxuriae, and continuous tegillum forming the periblast. The degree of contact at the limbi between tegillum and endoblast is highly variable, from closely appressed to separated except at the archeopyle suture. Processes are hollow, box-like to tubular, open or closed, often perforate, and distally expanded and/or denticulate. The periblast sags between processes such that the process shafts decrease in length with increasing cavation; in highly inflated specimens only distal claustra and/or ornamentation indicate the tabulation. The archeopyle is apical, Type (4A), with a characteristically rounded margin. Ventrally, a low, geniculate protrusion is formed by the anterior sulcal field which contacts the fourth apical sensu lato (as and !4`), to the exclusion of the sixth precingular and first apical sensu lato (6" and !1`). The indicated tabulation is 4`, 6", xc, xs, p, 5-6"`, 1"" sexiform L-type; the hypocyst exhibits dextral torsion with the 4"`/5"` field boundary occurring mid-dorsally; a single large process indicates that the antapex is dominated by 1"".
Remarks:
It may be noted that in many cavate genera, contact between the endoblast and periblast occurs ventrally or laterally, so that a separate endoarcheopyle and periarcheopyle is present. In circumcavate specimens of Cousteaudinium, the only contact between the two blasts occurs at the apical archeopyle margin and the corresponding opercular margin.
Discussion:
The new genus Cousteaudinium, is referred to the gonyaulacacean subfamily Cribroperidinioideae Fensome et al. 1993 based on dextral torsion in the hypotabulation and a general L-type ventral tabulation, despite the occurrence of an as/!4` field boundary.
The tabulation of the type species of Cousteaudinium gen. nov, as far as can be determined, is the same as for Hystrichokolpoma rigaudiae. Specifically, the apical archeopyle is rounded, with the anterior sulcal field making narrow contact with the fourth apical sensu lato, and 4"`/5"` occurs mid-dorsally with 4"` and 5"` being essentially symmetrical about the sulcal plane. The wall microstructure of these two species is also highly similar, further suggesting a close evolutionary relationship between them. In the type species of Hystrichokolpoma, Hystrichokolpoma cinctum, 6" contacts 1`, resulting in a shallow anterior sulcal notch and the absence of an as/!4` boundary. However, several other species of Hystrichokolpoma, for example Hystrichokolpoma torquatum Damassa 1979, exhibit the alternative as/4` field boundary found in Cousteaudinium.
Manum et al. (1989) illustrated undescribed specimens from the Norwegian Sea, as Dinocyst sp. 4, Dinocyst sp. 5 and Dinocyst sp. 7, that may be assignable to Cousteaudinium.
Affinities:
What distinguishes Cousteaudinium from Hystrichokolpoma, in addition to the absence of cingular processes, is the fact that most specimens develop a circumcavate pericoel such that the endoblast and periblast are in contact only at the archeopyle suture. The absence of inter-process cavation in all of the Paleogene species of Hystrichokolpoma, and the development of analogous cavation in other Neogene genera such as Amiculosphaera and Invertocysta, suggest to us that cavation in Cousteaudinium represents a cyst morphological adaptation of generic significance.
Cousteaudinium differs from Oligosphaeridium, which also lacks cingular processes and has an apical archeopyle, and from other leptodinioidean genera, in having a circumcavate wall structure with broad box-like processes, and in several details of the tabulation, notably dextral torsion of the hypotabulation. These features also separate the new genus from quinqueform Hystrichosphaeridium and other goniodomacean genera. Among cribroperidinioidean genera with an apical archeopyle, Cousteaudinium is most similar to Hystrichokolpoma as discussed.
[Cousteaudinium, de Verteuil and Norris, 1996a, p. 109, 111
Type species: Cousteaudinium aubryae, de Verteuil and Norris, 1996a (pl.1, figs.1–3,6,9)]
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [de Verteuil and Norris, 1996]:
Diagnosis:
Circumcavate and variably chorate gonyaulacacean cysts lacking cingular processes and having an apical archeopyle; tabulation otherwise variably expressed by intratabular processes, usually one per field; fields in the sulcal and posterior ventral area with or without processes.
Original description:
The wall comprises the pedium, with or without proximate luxuriae, and continuous tegillum forming the periblast. The degree of contact at the limbi between tegillum and endoblast is highly variable, from closely appressed to separated except at the archeopyle suture. Processes are hollow, box-like to tubular, open or closed, often perforate, and distally expanded and/or denticulate. The periblast sags between processes such that the process shafts decrease in length with increasing cavation; in highly inflated specimens only distal claustra and/or ornamentation indicate the tabulation. The archeopyle is apical, Type (4A), with a characteristically rounded margin. Ventrally, a low, geniculate protrusion is formed by the anterior sulcal field which contacts the fourth apical sensu lato (as and !4`), to the exclusion of the sixth precingular and first apical sensu lato (6" and !1`). The indicated tabulation is 4`, 6", xc, xs, p, 5-6"`, 1"" sexiform L-type; the hypocyst exhibits dextral torsion with the 4"`/5"` field boundary occurring mid-dorsally; a single large process indicates that the antapex is dominated by 1"".
Remarks:
It may be noted that in many cavate genera, contact between the endoblast and periblast occurs ventrally or laterally, so that a separate endoarcheopyle and periarcheopyle is present. In circumcavate specimens of Cousteaudinium, the only contact between the two blasts occurs at the apical archeopyle margin and the corresponding opercular margin.
Discussion:
The new genus Cousteaudinium, is referred to the gonyaulacacean subfamily Cribroperidinioideae Fensome et al. 1993 based on dextral torsion in the hypotabulation and a general L-type ventral tabulation, despite the occurrence of an as/!4` field boundary.
The tabulation of the type species of Cousteaudinium gen. nov, as far as can be determined, is the same as for Hystrichokolpoma rigaudiae. Specifically, the apical archeopyle is rounded, with the anterior sulcal field making narrow contact with the fourth apical sensu lato, and 4"`/5"` occurs mid-dorsally with 4"` and 5"` being essentially symmetrical about the sulcal plane. The wall microstructure of these two species is also highly similar, further suggesting a close evolutionary relationship between them. In the type species of Hystrichokolpoma, Hystrichokolpoma cinctum, 6" contacts 1`, resulting in a shallow anterior sulcal notch and the absence of an as/!4` boundary. However, several other species of Hystrichokolpoma, for example Hystrichokolpoma torquatum Damassa 1979, exhibit the alternative as/4` field boundary found in Cousteaudinium.
Manum et al. (1989) illustrated undescribed specimens from the Norwegian Sea, as Dinocyst sp. 4, Dinocyst sp. 5 and Dinocyst sp. 7, that may be assignable to Cousteaudinium.
Affinities:
What distinguishes Cousteaudinium from Hystrichokolpoma, in addition to the absence of cingular processes, is the fact that most specimens develop a circumcavate pericoel such that the endoblast and periblast are in contact only at the archeopyle suture. The absence of inter-process cavation in all of the Paleogene species of Hystrichokolpoma, and the development of analogous cavation in other Neogene genera such as Amiculosphaera and Invertocysta, suggest to us that cavation in Cousteaudinium represents a cyst morphological adaptation of generic significance.
Cousteaudinium differs from Oligosphaeridium, which also lacks cingular processes and has an apical archeopyle, and from other leptodinioidean genera, in having a circumcavate wall structure with broad box-like processes, and in several details of the tabulation, notably dextral torsion of the hypotabulation. These features also separate the new genus from quinqueform Hystrichosphaeridium and other goniodomacean genera. Among cribroperidinioidean genera with an apical archeopyle, Cousteaudinium is most similar to Hystrichokolpoma as discussed.