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Odontochitina ancala
Odontochitina ancala Bint, 1986
Holotype: Bint, 1986, pl.1, figs.5-6
Locus typicus: Western Interior, U.S.A.
Stratum typicum: Middle-Late Albian
Original description: Bint, 1986, p.139-140
Large cysts with ceratioid outline and three long, pointed horns, apical, antapical, and right lateral. Right lateral horn extends at nearly right angles to the endocyst margin for a short distance then recurves posteriorly, with a cingular notch at the point of recurvature. Cornucavate; endocyst subspherical or produced slightly into horn bases, with circular equatorial section. Periphragm separated from endophragm at horns, but hypocystal pericoels may be enlarged beyond bases. The antapical pericoel has an elongate extension up the left ventral surface usually as far as the cingulum. Endophragm smooth, periphragm smooth or scabrate, but with a distinctive concentration of perforations, at least 10-15 in number and commonly more than 20, about midway along each horn, especially the hypocystal horns. Perforations typically subcircular and usually 1-3 µm in diameter but some may be larger. Larger perforations may be elliptical with long axes about parallel to horns. When perforations are well developed, the hypocystal horns are noticeably constricted immediately beyond their perforate portion. Archeopyle apical, type (tA), operculum free. Archeopyle suture weakly angular, sulcal notch mid-ventral to slightly offset to the left. Paratabulation not expressed. Cingulum indicated by faint transverse lines to low parasutural ridges, but always absent on right side of ventral surface; also indicated by a distinct notch in the right lateral horn. Left edge of sulcus probably delimited by ventral extension of antapical cavation.
Size. Endocyst diameter 45(56)69 µm; length of two complete specimens 215 and 223 µm; length with operculum detached 88(117)154 µm, 18 measurements; length of lateral horn 28(49)73 µm and antapical horn 33(65)89 µm; 20 specimens measured. Length of three detached opercula 138-170 µm, apical horn 111-136 µm.
Remarks. The species shows considerable variation in horn length and in the number and size of perforations on the horns. Moreover, these two features seem to be interrelated. Long-horned specimens similar to O. operculata tend to have fewer and smaller perforations on the horns; as horn length decreases the perforations increase in number and size. Plate 7, figs. 1, 2 show the two extremes of this morphologic continuum.
Affinities:
Bint, 1986, p.140: Odontochitina ancala differs from O. operculata by having an elbow and cingular notch in the right lateral horn, localized perforations about midway along the horns, and an elongate ventral extension of the antapical pericoel. In these samples some specimens of O. operculata may have a few localized perforations or a slightly extended antapical pericoel, but the lack of an elbow and cingular notch distinguishes them from O. ancala. However, O. ancala is thought to have developed from O. operculata by introduction of the elbow in the lateral horn and progressive development of the localized perforations and antapical pericoel extension. O. imparilis is similar to O. ancala in having an elbow in the lateral horn and apparently some extension of the antapical periocoel up the ventral side, but it is distinguished by the complete absence of perforations on the horns. That species tends to have the hypocystal cornucavations enlarged beyond the horn bases and connected, and also to have a small left lateral bulge as a result of the expression of the cingulum. Both these features rarely occur on O. ancala. O. costata differs in lacking the elbow in the lateral horn and the ventral extension of the antapical pericoel, and in having longitudinally arranged perforations and striae.
Holotype: Bint, 1986, pl.1, figs.5-6
Locus typicus: Western Interior, U.S.A.
Stratum typicum: Middle-Late Albian
Original description: Bint, 1986, p.139-140
Large cysts with ceratioid outline and three long, pointed horns, apical, antapical, and right lateral. Right lateral horn extends at nearly right angles to the endocyst margin for a short distance then recurves posteriorly, with a cingular notch at the point of recurvature. Cornucavate; endocyst subspherical or produced slightly into horn bases, with circular equatorial section. Periphragm separated from endophragm at horns, but hypocystal pericoels may be enlarged beyond bases. The antapical pericoel has an elongate extension up the left ventral surface usually as far as the cingulum. Endophragm smooth, periphragm smooth or scabrate, but with a distinctive concentration of perforations, at least 10-15 in number and commonly more than 20, about midway along each horn, especially the hypocystal horns. Perforations typically subcircular and usually 1-3 µm in diameter but some may be larger. Larger perforations may be elliptical with long axes about parallel to horns. When perforations are well developed, the hypocystal horns are noticeably constricted immediately beyond their perforate portion. Archeopyle apical, type (tA), operculum free. Archeopyle suture weakly angular, sulcal notch mid-ventral to slightly offset to the left. Paratabulation not expressed. Cingulum indicated by faint transverse lines to low parasutural ridges, but always absent on right side of ventral surface; also indicated by a distinct notch in the right lateral horn. Left edge of sulcus probably delimited by ventral extension of antapical cavation.
Size. Endocyst diameter 45(56)69 µm; length of two complete specimens 215 and 223 µm; length with operculum detached 88(117)154 µm, 18 measurements; length of lateral horn 28(49)73 µm and antapical horn 33(65)89 µm; 20 specimens measured. Length of three detached opercula 138-170 µm, apical horn 111-136 µm.
Remarks. The species shows considerable variation in horn length and in the number and size of perforations on the horns. Moreover, these two features seem to be interrelated. Long-horned specimens similar to O. operculata tend to have fewer and smaller perforations on the horns; as horn length decreases the perforations increase in number and size. Plate 7, figs. 1, 2 show the two extremes of this morphologic continuum.
Affinities:
Bint, 1986, p.140: Odontochitina ancala differs from O. operculata by having an elbow and cingular notch in the right lateral horn, localized perforations about midway along the horns, and an elongate ventral extension of the antapical pericoel. In these samples some specimens of O. operculata may have a few localized perforations or a slightly extended antapical pericoel, but the lack of an elbow and cingular notch distinguishes them from O. ancala. However, O. ancala is thought to have developed from O. operculata by introduction of the elbow in the lateral horn and progressive development of the localized perforations and antapical pericoel extension. O. imparilis is similar to O. ancala in having an elbow in the lateral horn and apparently some extension of the antapical periocoel up the ventral side, but it is distinguished by the complete absence of perforations on the horns. That species tends to have the hypocystal cornucavations enlarged beyond the horn bases and connected, and also to have a small left lateral bulge as a result of the expression of the cingulum. Both these features rarely occur on O. ancala. O. costata differs in lacking the elbow in the lateral horn and the ventral extension of the antapical pericoel, and in having longitudinally arranged perforations and striae.