Caron (1985):
S. cenomana differs from the other Schackoina species in having 4 chambers in the last whorl, each with a single tubulospine.
Boudagher-Fadel et al. (1997):
Remarks: In 1897, Schacko described random thin-sections of planktonic foraminifera from the Cenomanian Chalk of Moltzow, Mecklenburg, Germany; these specimens had four chambers in the last of a succession of whorls, and these late chambers were narrowly elongated into 'tubulospines' (sensu Bolli, Loeblich and Tappan, 1957).
Schacko (1897) called these forms Siderolina cenomana, but Siderolina is a d'orbigny genus (recte Siderolites) which is totally unrelated; Thalmann (1932) placed them in his new genus
Schackoina as its type species. The existence of the type specimens of S. cenomana has never been established but hypotypes ('near topotypes') were figured by Bolli, Loeblich and Tappan (1957, pl. 2, figs 1, 2) from the Cenomanian of Luneburg, Germany. One of these specimens (Ibid., plate 2,
figs la-c; reproduced in our Plate 10.7, Figs 1-3) is formally chosen here as the neotype, because it matches the original syntypes and is from a
locality as near as possible to them and is, as far as we know, of the same age. Masella (1960) figured very many specimens of Schackoina (solid and thin-sectioned) from the Cenomanian of Sicily; she referred them to many subspecies of cenomana, including four-chambered forms as S. cenomana ss. (believed to range from the
Cenomanian to the Turonian), five-chambered
forms as S. pentagonalis Reichel, 1948 (Albian-
Coniacian) and many others. Many of the thin
sections drawn by Masella (1960) showed initial
trochospiral whorls (buried by the adult involute
planispiral) and the tubulospines of the early
planispiral whorls preserved inside the adult chambers
(which usually have their spines broken off).
The youngest Schackoina was recorded from the
Maastrichtian by Aurouze and de Klasz (1954).
Schackoina differs from the older and shorterranged
Leupoldina in having narrowly elongate
tubulospines and in lacking the bulbous terminations to the elongate chambers typical of Leupoldina, even though, like Leupoldina, its last chambers may become bi- or even tri-serial, with its tubulospines becoming multiple on the final chambers. Schackoina differs from the Eocene genus Hantkenina, its larger, gross homeomorph, in possessing the smooth, microperforate wall typical
of the Schackoinidae and Praehedbergellidae, and also in possessing trochospiral initial whorls and in having tubulospines which are thin-walled yet having broad inner spaces (Hantkenina has tubulospines which are thick-walled with very narrow inner spaces); these two genera are thus easily distinguished both in the solid specimen and in random thin-section.
Schackoina cenomana has four chambers in the last whorl and is very involute; its umbilici are very small and narrow.
Pflaumann & Krasheninnikov (1977):
This tiny species, often smaller than 120 ìm in diameter, has been
recorded from Cenomanian rocks nearly all over the world. Late
Albian occurrences have been reported by Herb (1974) from the
eastern Indian Ocean. |
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