MILIOLIDAE - Acta Palaeontologica Polonica

MILIOLIDAE FROM MIOCENE OF POLAND 31
(e.g. Serova, 1955, PI. 9, Figs 13-15). It follows that, excepting the genus
Quinqueloculina, the juvenile stage of other genera has no differentiated
diagnostic characters.
4) Within the genus Sinuloculina there are species whose juvenile stage
differs so much from the adult stage that these two stages are often
identified as separate species (e.g. in Sinuloculina microdon, Part 1 1
Textfig.
10).
As regards the aperture and tooth, their shape in the juvenile stage
may differ from that in the adult stage, which can be exemplified by the
genus Varidentella. In V. sarmatica and V. reussi there occur adult specimens
which have a toothless aperture, but removing their external chambers
successively, one can find that in the juvenile stage the aperture is
furnished with a well-developed broad tape-shaped tooth. Hauerina and
Miliola have two types of the aperture and tooth; in the juvenile stage
the aperture is round with a simple tooth, as in Siphonaperta or Cycloforina,
whereas in the adult stage of both genera a cribrate plate develops
and covers both the aperture and the tooth. (e.g. Miliola fabularoides,
PI. XIV, Figs 1-3). This fact has also been stated by Serova (1953 and
1960).
RELATED FORMS
It has been found that groups of such forms that their affinity is
visible both in the similar structure of the juvenile stage and in some
morphological characters in the adult stage and also in the similar nature
of the walls can be distinguished in the Miliolidae from the Miocene of
Poland. As early as 1912 Wiesner paid attention to the existence of
different types of walls in the contemporary Miliolidae and tried to utilize'
this fact in classification (see the section "History of Studies on the Miliolidae").
The group mentioned in the preceding section and composed of Cycloforina
contorta, C. lachesis, C. lucida and C. gracilis, which occur together
in the deposits of the Upper Tortonian at Gliwice Stare, is conspicuous
among the Miocene forms under study. As has been mentioned, this group
is characterized by a similar juvenile stage, consisting of identical tubular
chambers, whereas the adult stage shows a character developing from
species to species, namely, the edges along the chambers. The initial form is
completely void of edges and has tubular chambers in both juvenile and
adult stages - C. gracilis. The next link, Cycloforina lucida, is less regular
and more elongate, with signs of flattenings in the periphery of chambers.
This feature develops further through the forms with two rounded edges
belonging to C. contorta and typical forms of this species with sharp edges,
to the last form of this row, C. lachesis, with a single keel, split only in
the lower portion of the chambers.