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Phthanoperidinium delicatum
Phthanoperidinium delicatum Michoux, 1985
Holotype: Michoux, 1985, pl.2, figs.1-4; text-fig.7
Age: Early-Middle Eocene
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Original description: [Michoux, 1985] (translated from French):
Phthanoperidinium delicatum n. sp.
(PI. 2, fig. 1-4; PI. 3, fig. 1-2, 3-4, 5, 13, 14; text-fig. 7)
Holotype: Slide G6-3, coordinates J52/4-K52/2.
Origin of the name: From the fine and delicate structure of the parasutural ridges.
Type locality: Gibret, marl-limestone with Discocyclines from the upper part of the Nousse beds, beneath the village school.
Diagnosis: Proximate, peridinioid, cornucavate cyst, slightly flattened dorsoventrally. Subcircular outline modified by an apical horn and two antapical horns. Paratabulation indicated by serrated parasutural ridges. Intercalary archaeopyle formed by the detachment of one to three intercalary paraplates.
Description: Proximate, peridinioid cyst. Subcircular, granular endophragm. Smooth periphragm, in contact with the endophragm except at the apex and antapex where it forms short, triangular horns (one apical horn, two antapical horns, the left slightly longer). The horns bear individual spines. The apical horn bifurcates distally from halfway up.
The periphragm forms thin, finely crenulated parasutural ridges, 5 to 7 μm high, reflecting the paratabulation. The pre- and postengulate paraplates are trapezoidal, sometimes rectangular. One of the characteristics of this species is the absence of a suture separating the 3'" paraplate from the overlying cingulum. The 1"" paraplate is smaller than the 2"" paraplate. The cingulum is slightly helical and undivided. It is interrupted ventrally by a broad sulcus that most often extends from the apex to the antapex.
However, in some specimens with better developed parasutures, the lateral limits of the 1' paraplate, which is diamond-shaped, as well as the ps paraplate, are distinguishable.
The archaeopyle is intercalary. It is most often formed by the loss of the three intercalary paraplates type 3 I (1 a-3 a). However, a lateral intercalary paraplate may remain attached (more rarely both), as is the case in the holotype (Pl. 2, fig. 1-4), where the paraplate 1a remained attached by the upper edge to the underlying precingulate plates.
Tabulation: 4', 3 a, 7", 5'", ps, 1"".
Dimensions: Height: 38 (53) 63 um; Width: 38 (47) 55 um; 25 specimens measured.
Discussion: Phthanoperidinium delicatum is similar to two species described by De Coninck, 1975, in the Ypresian of Belgium, P. crenulatum and P. schizokeras. Both possess ornamentation consisting of serrated parasutural ridges and an intercalary archaeopyle of type 3 I (1 a-3 a). P. crenulatum is rounded in shape like P. delicatum but is distinguished by the constant presence of the parasutural ridge separating the paraplate 3'" of the cingulum, a ridge that is always missing in P. delicatum.
This ridge is also present in P. schizokeras. This form is more elongated than in P. delicatum. The author further specifies that it is not possible to recognize individual horns at the antapex, and that the apical horn is divided from its base and not from halfway up as in P. delicatum.
Caro, 1973, described Phthanoperidinium campoense in the Campo section, the parastratotype of the Ilerdian. This species, like P. delicatum, possesses parasutural ridges and a 3 I archaeopyle. The only specimen observed by the author differs in the following characteristics: 1) a shorter apical horn and undeveloped antapical horns; 2) the presence of a ridge separating 3'" of the cingulum; 3) the presence of a single antapical plate.
Holotype: Michoux, 1985, pl.2, figs.1-4; text-fig.7
Age: Early-Middle Eocene
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Original description: [Michoux, 1985] (translated from French):
Phthanoperidinium delicatum n. sp.
(PI. 2, fig. 1-4; PI. 3, fig. 1-2, 3-4, 5, 13, 14; text-fig. 7)
Holotype: Slide G6-3, coordinates J52/4-K52/2.
Origin of the name: From the fine and delicate structure of the parasutural ridges.
Type locality: Gibret, marl-limestone with Discocyclines from the upper part of the Nousse beds, beneath the village school.
Diagnosis: Proximate, peridinioid, cornucavate cyst, slightly flattened dorsoventrally. Subcircular outline modified by an apical horn and two antapical horns. Paratabulation indicated by serrated parasutural ridges. Intercalary archaeopyle formed by the detachment of one to three intercalary paraplates.
Description: Proximate, peridinioid cyst. Subcircular, granular endophragm. Smooth periphragm, in contact with the endophragm except at the apex and antapex where it forms short, triangular horns (one apical horn, two antapical horns, the left slightly longer). The horns bear individual spines. The apical horn bifurcates distally from halfway up.
The periphragm forms thin, finely crenulated parasutural ridges, 5 to 7 μm high, reflecting the paratabulation. The pre- and postengulate paraplates are trapezoidal, sometimes rectangular. One of the characteristics of this species is the absence of a suture separating the 3'" paraplate from the overlying cingulum. The 1"" paraplate is smaller than the 2"" paraplate. The cingulum is slightly helical and undivided. It is interrupted ventrally by a broad sulcus that most often extends from the apex to the antapex.
However, in some specimens with better developed parasutures, the lateral limits of the 1' paraplate, which is diamond-shaped, as well as the ps paraplate, are distinguishable.
The archaeopyle is intercalary. It is most often formed by the loss of the three intercalary paraplates type 3 I (1 a-3 a). However, a lateral intercalary paraplate may remain attached (more rarely both), as is the case in the holotype (Pl. 2, fig. 1-4), where the paraplate 1a remained attached by the upper edge to the underlying precingulate plates.
Tabulation: 4', 3 a, 7", 5'", ps, 1"".
Dimensions: Height: 38 (53) 63 um; Width: 38 (47) 55 um; 25 specimens measured.
Discussion: Phthanoperidinium delicatum is similar to two species described by De Coninck, 1975, in the Ypresian of Belgium, P. crenulatum and P. schizokeras. Both possess ornamentation consisting of serrated parasutural ridges and an intercalary archaeopyle of type 3 I (1 a-3 a). P. crenulatum is rounded in shape like P. delicatum but is distinguished by the constant presence of the parasutural ridge separating the paraplate 3'" of the cingulum, a ridge that is always missing in P. delicatum.
This ridge is also present in P. schizokeras. This form is more elongated than in P. delicatum. The author further specifies that it is not possible to recognize individual horns at the antapex, and that the apical horn is divided from its base and not from halfway up as in P. delicatum.
Caro, 1973, described Phthanoperidinium campoense in the Campo section, the parastratotype of the Ilerdian. This species, like P. delicatum, possesses parasutural ridges and a 3 I archaeopyle. The only specimen observed by the author differs in the following characteristics: 1) a shorter apical horn and undeveloped antapical horns; 2) the presence of a ridge separating 3'" of the cingulum; 3) the presence of a single antapical plate.