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Xenascus plotei
Xenascus plotei Below, 1981
Holotype: Below, 1981, pl.2, fig.9; text-fig.10; Fensome et al., 1991, figs.2-3 - p.713
Paratype: Below, 1981, pl.2, fig.8; pl.8, fig.21
Locus typicus: Between Sidi Ahmed ou Rami and Tizi, SW Morocco
Stratum typicum: Aptian-Cenomanian
Translation Below, 1981: Fensome, 1991, p. 714-715
Original diagnosis: Below, 1981, p. 21
Cornucavate, nontabulate cyst. Endocyst spheroidal, ovoidal or rhomboidal. Pericyst of the same shape, appressed to the inner body. Pericoels confined to the lumina of three short appendages. Apical horn cylindrical or pointed/conical, antapical horn conical, with a broad base. These two polar protuberances are usually distally rounded and perforate. The lateral horn is also short, perforate distally and has a pointed end. The cyst and the bases of the horns bear a few, irregularly placed acuminate spines of varying size. Equatorially they are dorsally connected to form rows which correspond to the posterior and anterior margins of the paracingulum. The archeopyle is of type (A). The endophragm is smooth, the periphragm smooth or with scattered, fine punctae.
Original description: Below, 1981, p. 21-22
The shape of the inner body varies from spheroidal to ovoidal or stoutly to elongately rhomboidal. Its short wart-like appendage extends apically into the cavity of the periphragmal apical horn. This is columnar, abruptly arising from the pericyst or, alternatively like the antapical horn, it has a broad base, tapers continuously to a point and is distally rounded. Both polar appendages are shorter than the length of the endocyst. The length of the pointed/conical, equatorial lateral horn corresponds approximately to the radius of the endocyst. The distal ends of the appendages are perforated and, consequently, easily destroyed and commonly broken off. Solid spines, which are taeniate to round in transverse section, are irregularly distributed over the central region of the cyst and at the bases of the horns. Distally they are usually acuminate, rarely capitate or finely bifurcate. On some specimens the spines are dorsally arranged in two rows which are obviously homologous to the margins of the paracingulum. Additional, hollow, conical processes were seldom observed. The number of processes varies substantially. For instance, some individuals bear only one or two small spines and even completely smooth specimens have been observed in the Moroccan material. The archeopyle opens by detachment of the apical cap, inclusive of the apical horn, and consequently corresponds to type (A).
Affinities:
Bint, 1986, p.144: Xenascus plotei is most similar to Odontochitina rhakodes from which it differs in bearing sparse spines on the periphragm. On some specimens spines are short and few in number suggesting that X. plotei may have developed from O. rhakodes by the addition of an ornament of spines. Other described species of Xenascus have longer and more complexly branched spines.
Holotype: Below, 1981, pl.2, fig.9; text-fig.10; Fensome et al., 1991, figs.2-3 - p.713
Paratype: Below, 1981, pl.2, fig.8; pl.8, fig.21
Locus typicus: Between Sidi Ahmed ou Rami and Tizi, SW Morocco
Stratum typicum: Aptian-Cenomanian
Translation Below, 1981: Fensome, 1991, p. 714-715
Original diagnosis: Below, 1981, p. 21
Cornucavate, nontabulate cyst. Endocyst spheroidal, ovoidal or rhomboidal. Pericyst of the same shape, appressed to the inner body. Pericoels confined to the lumina of three short appendages. Apical horn cylindrical or pointed/conical, antapical horn conical, with a broad base. These two polar protuberances are usually distally rounded and perforate. The lateral horn is also short, perforate distally and has a pointed end. The cyst and the bases of the horns bear a few, irregularly placed acuminate spines of varying size. Equatorially they are dorsally connected to form rows which correspond to the posterior and anterior margins of the paracingulum. The archeopyle is of type (A). The endophragm is smooth, the periphragm smooth or with scattered, fine punctae.
Original description: Below, 1981, p. 21-22
The shape of the inner body varies from spheroidal to ovoidal or stoutly to elongately rhomboidal. Its short wart-like appendage extends apically into the cavity of the periphragmal apical horn. This is columnar, abruptly arising from the pericyst or, alternatively like the antapical horn, it has a broad base, tapers continuously to a point and is distally rounded. Both polar appendages are shorter than the length of the endocyst. The length of the pointed/conical, equatorial lateral horn corresponds approximately to the radius of the endocyst. The distal ends of the appendages are perforated and, consequently, easily destroyed and commonly broken off. Solid spines, which are taeniate to round in transverse section, are irregularly distributed over the central region of the cyst and at the bases of the horns. Distally they are usually acuminate, rarely capitate or finely bifurcate. On some specimens the spines are dorsally arranged in two rows which are obviously homologous to the margins of the paracingulum. Additional, hollow, conical processes were seldom observed. The number of processes varies substantially. For instance, some individuals bear only one or two small spines and even completely smooth specimens have been observed in the Moroccan material. The archeopyle opens by detachment of the apical cap, inclusive of the apical horn, and consequently corresponds to type (A).
Affinities:
Bint, 1986, p.144: Xenascus plotei is most similar to Odontochitina rhakodes from which it differs in bearing sparse spines on the periphragm. On some specimens spines are short and few in number suggesting that X. plotei may have developed from O. rhakodes by the addition of an ornament of spines. Other described species of Xenascus have longer and more complexly branched spines.