ORNAMENTAL AND SHAPE VARIATION IN Hemicytherura fulva McKENZIE, REYMENT AND REYMENT (OSTRACODA; EOCENE, AUSTRALIA)

Hemicytherura fu/va displays ornamental variation of two kinds. One of these (termed _the m_orph LACE) is vaguely linked to shape and is generally dilferently distributed from the rest of the material; th1s morph may possess intrinsic evolutionary significance. The other categories are probably ecophenotypic in nature. Methods of distance­ based mullivariate morphometry and geometric morphometry were used for the shape study.


INTRODUCfION
Covariation in shape and ornament in species of an ostracod genus was investigated by Reyment (1985). 1t was found that in Eocene species of Echinocythereis from northern Spain, shape modifications were correla ted with irreversible changes in ornament. That study could, however, only point to the possibility that there was a genetic relationship between the two categories, but could not prove that any genuine pleiotropic conne xion really existed. More recently, Jrizuki and Sasaki (1993) at the Eleventh lnternational Symposium on Ostra coda, Warrnambool, Australia interpreted morphologi cal variation in recent species of ostracods in terms of heterochrony, although without providing a biometrical basis for their conclusions.
The preliminary scanning of all of the material available of Hemicytherura fu/va McKenzie, Reyment and Reyment, of Eocene age, suggested the possibility of that species being polymorphic with respect to shape. It was also observed that there was ornamental poly morphism in the material that could perhaps in part be linked to the suspected variability in shape.
A suitable means of testing hypotheses about mor phological variations in shape, with and without the intervention of size, is provided by the tensor-biometrical methods of Bookstein (1991), supported, where rele van!, by standard methods of multivariate statistical analy sis (Reyment et al., 1984); that is, multivariate analyses made on the usual distance measures -lengths, heights, breadths etc., of quantitative taxonomic work. Current concepts of multivariate morphometrics contrast with the original scope defined by Blackith and Reyment ( 1971 ); the new synthesis may be regarded as a pragma tic fusion of geometric morphometry and ''phenometry". It is important that this distinction be kept in mind in what follows.
Complications occasioned by sexual dimorphism had to be taken into account in the analysis. It was assumed that where sexual-dimorphic differences did exist, the morphological differentiation would show up when size was allowed to remain in the computations. Reasonably well supported identifi cations of males are indicated in the figures.
As always in studies involving ornamental variabi lity in the ostracod carapace, it is necessary to be aware of the possibility that quite marked differences in orna mental patterns can be caused by a deficiency or a superfluity of calcium ions during moulting and secre ting a new shell (McKenzie and Peypouquet, 1984). Hence, the "lacelike ornament" reported in the follo wing is like what results from a deficiency of calcium carbonate, and the thickly ribbed variant resembles a common product of supersaturation with calcium. I am inclined to dismiss the likelihood of the concentration of calcium ions as being the motor of ornamental varia tion in the present case beca use of the rarity of the two variants of interest and the fact that I can see no externa! evidence likely to support the supersaturation model in the sedimentary properties of the samples I have had at my disposal.