Ontogenesis and stratigraphy of the ostracod Veeniacythereis jezzineensis (Bischoff, 1963)

Veeniacythereis jezzineensis (Bischoff, 1963) occurs in Israel throughout the Upper Albian-Cenomanian. It comprises continuously ornamented-variable forms, including A-3 to A molt stages. The ontogenetic lineages reveal a pre-adult sexual-dimorphism. It is suggested that Cythereis maghrebensis Bassoullet & Damotte and Cythereis streblolophata Al-Abdul-Razzaq & Grosdidier are junior synonyms of V. jezzineensis.


INTRODUCTION
Thle history of the forms designated herein as Veeniacythereis jezzineensis, began in 1959, when Glintzboeckel & MagnC illustrated their ostracods C 1, C 2 and C3 from East Algeria and Tunisia. Since then, these forms have been described and figured in a dozen publications (see synonymy) and their stratigraphy given. Unfortunately, there is no consensus about the taxonomy of thlese forms, and a variety of specific and subspecific names, as well as different generic definitions, were attributed to these same forms. This has, of course, led to controversy concerning their stratigraphic position.
V . jezzineensis is very abundant throughout Israel, occui-ring from the uppermost Albian Hevyon Member to the Upper Cenomanian, Avnon Member of the Hazera Formation, and in the Moza Formation. (Rlosenfeld & Raabl, 1974). Several samples included rich aissemblages of this species enabling a thorough syste:matic and ontogenetic study.

Dimensions.
In order to follow the ontogenetical series, the lengths and heights of some 170 specimens from 30 samples, and belonging to V. jezzineensis according to our concept, were measured and plotted (Fig. 1). Fig. 1 shows clearly the discontinuous growth pattern of the molt stages and the distinct lineages of the males and females. Sexual dimorphism is observed relatively early in ontogeny, as early as stage A-2. This phenomenon of early sexual dimorphism in ostracods has been previously discussed in the literature (Rohr, 1979;Whatley & Stephens, 1977). Despite its inaccuracy, the plottings of the minimum and maximum range values of the lengths and heights of the original descriptions of C. jezzineensis Bischoff (1963, p. 43), and of C. maghrebensis Bassoullet & Damotte (1969, p. 133) fall well within our fields. The dimension ranges of Cythereis streblolophata streblolophata and C. streblolophata schista (Al-Abdul- Razzaq & Grosdidier, 1981, pp. 183, 185) fall within the fields of A-1 and A-2 stages with slight deviations. Ornamentation. There is no point in repeating the descriptions of the species, especially those features such as general shape, hinge ear, ridges etc., as they are commonly accepted. However, several points pertaining to the variability of ornament deserve consideration.
On the basis of observation of the numerous specimens it is obvious that the ornament is transitionally variable. The pattern of a median ridge accompanied by ventral and dorsal ridges exists in all the specimens, however, these ridges may vary in strength, from thin to very thick and prominent. Another variable feature is the cross ridglets, which may traverse continuously from the dorsal to the ventral ridges, or may be interrupted to various degrees. In addition, it could be observed that the transverse ridges are relatively few in early stages,

All figures are x 80
Veeniacythereis jezzineensis (Bischoff) becoming more numerous towards the adult stage. (e.g. A-3: 4-5; A-2: 6 ; A : 7-8). The subcentral knob appears in earlier stages as a thickening on the rib, either connected t o , o r separated from the eye spot, becoming a thick, oval, reticulated knob in the adult. The reticulation exists o n l y in the adult stage, which otherwise keeps all the above mentioned features.

REMARKS
The above mentioned synonymy includes all the available publication4 which, in our opinion, deal with V . jezzineensis. These descriptions fall within one or other of the stages of this species, and completely agree with the descriptions of the respective stage. It seems that the variability in ornament, which accompanies the molt stages led several authors (e.g. Bassoullet 61 Damotte, 1969;AI-Abdul-Razzaq & Grosdidier, 1981 ; Bismuth e f ul., 1981) to assign their specimens to different species and occasionally even genera.
In this connection it should be mentioned that the hinges shown by Al-Abdul- Razzaq & Grosdidier (1981, pl.  anterior and posterior teeth whereas the median groove is crenulated. This hinge is typical of the amphidonti heterodont hinge of Veenia (and Veeniacythereis Grundel, 1974, p. 1469, rather than the amphidont: lobodont hinge of Cythereis (Van Morkhoven, 1962, p. 180). Unfortunately our samples contained very few single valves and these were very badly preserved. Therefore a thorough discussion on the hinge pattern of either juveniles or adults is impeded. However, to the best of our knowledge the hinge pattern in juveniles, and its ontogenetic development in the group of Veeniacythereis has not yet been thoroughly studied, and no conclusion can be categorically drawn, based on the stage of development of the hinge.