Bennelongia, De Deckker & McKenzie, 1981

Deckker, Patrick De & Martens, Koen, 2013, Extraordinary morphological changes in valve morphology during the ontogeny of several species of the Australian ostracod genus Bennelongia (Crustacea, Ostracoda), European Journal of Taxonomy 36, pp. 1-37 : 8-9

Bennelongia cf. barangaroo nov. sp.

Figs 16-18

Bennelongia dedeckkeri Shearn, Koenders, Halse, Schön & Martens, 2012

Figs 19-21

We examined specimens of B. cf. barangaroo nov. sp. from McNeil Claypan in Western Australia and of B. dedeckkeri from Lake Dunn in Queensland. From the former locality, we only had A-1 and A-2, but from the latter we also had specimens of stages A-3 and A-4.

Both species have a very similar appearance and are closely related. Their ontogeny is here discussed together.

The broad morphological characteristics of these species are, in many ways, similar to those of B. gwelupensis Martens et al., 2012 (see below) for the following reasons: pseudo-punctation is visible on the outer surface of the valves in A- 1 specimens ( Fig. 16 with 8 lateral views), more pronounced reticulation is obvious in A-2 and much more prominent in A- 3 specimens ( Fig. 17 with dorsal views), although there are areas in the dorsal and postero-dorsal regions which appear smooth, but this may be seen on specimens that were not fully calcified. The domes are somewhat visible in A- 2 specimens and more obvious in A- 3 specimens ( Fig. 16 ). The cones with outer lips and setae are clearly visible ( Fig. 19 , middle), but overall these conical features are much fewer than in B. gwelupensis . Nevertheless, the pores penetrate through the entire valves and are seen from the inside ( Fig. 18 , bottom left). Once again, the inner lamella and selvage are present in A- 1 specimens, but not as broad as in B. gwelupensis (see below).

The pattern in the younger instars remains the same: the valves of younger instars are more reticulated on the outside, the domes appear to be faintly distinguishable in A-1 and A- 2 specimens ( Figs 18-19 ) and are much more prominent in A-3 and even more so in A- 4 specimens. The domes in these earlier stages appear to be overgrown and display some reticulation that resembles some pseudo-punctation, but may be the result of over-calcification. They also possess the ubiquitous single sieve pores with seta ( Fig. 21 ), also seen in all other species discussed here.

The nature of the reticulation around the domes ( Fig. 20 ) is somewhat puzzling in its arrangement, as it is reminiscent of an irregular meshwork. A better understanding of the process of calcification may help understand how this feature is formed.

Once again, the domes differ in size ( Fig. 21 ), and in these species, the posterior one is the largest of the two.

The pseudo-punctation is obvious in A-1 and A- 2 specimens but would have replaced the reticulated nature of the outer valves as seen in A-3 and A-4 ( Fig. 20 ). The cones are present especially near the anterior and posterior margins of the valves, but are definitely not abundant. In the vicinity of the domes, the cones are quite small, but retain their outer lip ( Fig. 21 ).

Figures

Fig. 16. Lateral views of carapaces of Bennelongia cf. barangaroo nov. sp. from McNeil Claypan. Left column displays carapace in right lateral view, right column shows carapaces in left lateral view. Note the pronounced asymmetry between the adult valves and the less-pronounced beak-like feature of the anteroventral region of the adult LV. Pseudo-punctation is more pronounced in the younger instars and the domes and cones are only clearly visible in A-3 specimens, although remnants remain in the last two juvenile stages.

Fig. 17. Dorsal views of carapaces of Bennelongia cf. barangaroo nov. sp. from McNeil Claypan. Observe the coarse reticulation in A-3 specimens and the pseudo-punctuation that becomes less visible with progressing ontogeny. The adult specimen in top left image displays some agglomeration of glue along the hinge, particularly in the anterior and posterior regions.

Fig. 18. Specimens of Bennelongia cf. barangaroo nov. sp. from McNeil Claypan, to show specific features of juvenile specimens. Top left image shows the poorly pronounced domes in the dorsal region of the LV of an A-3 specimen. Top right image shows an internal view of an A-3 that shows the less pronounced inner list and the depression located opposite the cones and the possible larger depression matching the external dome. The middle images show the cones with the lips near their apex. Bottom left image shows the larger pores on the inside of the valve, that are connected to the opening of each pore on the apex of each cone. Bottom right corner image shows the highly reticulated texture of an A-3 valve and the domes that are not as pronounced as in other Bennelongia species (e.g., compare to B. nimala nov. sp. in Fig. 3).

Fig. 19. Dorsal views of carapaces of Bennelongia dedeckkeri Shearn et al., 2012 from Lake Dunn (Queensland) for the last 4 instars (A-4 toA-1) and the adult to show the changes in external ornamentation and the progressive disappearance of the domes and cones with ontogeny, such that at the adult stage, there is no ornamentation. Observe the presence of outer lists in all juvenile specimens clearly visible in the antero-dorsal region.

Fig. 20. Lateral views of carapaces of Bennelongia dedeckkeri Shearn et al., 2012 from Lake Dunn for the last 3 instars (A-3 to A-1) to show the changes in external ornamentation and the progressive disappearance of the domes and cones with ontogeny. Right lateral views are displayed in the top 3 left images, and left lateral views on the right. Details of the cones (bottom left) and the domes with fewer cones (bottom right) of A-3 specimens are portrayed. Note the presence of nodules stuck to the anterior portion of the valve of bottom left specimen.

Fig. 21. Detailed views of carapaces of Bennelongia dedeckkeri Shearn et al., 2012 from Lake Dunn to show the domes in both images and 4 cones in the top image of an A-3 specimen, and only one cone in the image of an A-4 specimen. Note the interlacing reticulation around the domes, and the small nodes coating the valves, with 2 different diameters best seen to the right of the largest dome. These nodules are thought to be part of the valve ornamentation.