Triebelina indopacifica, van den Bold, 1946, van den Bold, 1946

Forel, Marie-Béatrice, Poulet-Crovisier, Nathalie, Korat, Lidija & Maddocks, Rosalie F., 2024, Ornate Bairdiidae (Ostracoda) in 3 dimensions: exploring carapace morphology and pore canals of Triebelina van den Bold, 1946, Nodobairdia Kollmann, 1963 and Mirabairdia Kollmann, 1963, Comptes Rendus Palevol 23 (11), pp. 137-159 : 150-152

TRIEBELINA INDOPACIFICA

Marginal pores

In Triebelina sp. , six large marginal spines are visible along the postero-ventral margin ( Fig. 9A, B). They are hollow, but no setae are associated with them. A tiny pore is also visible at the base of each spine (Figs 5A; 9B), which houses the marginal setae (eyelash setae ofMaddocks 2013). The associated radial pore canals cannot be tracked through the entire thickness of the valve wall because of low resolution. The two adult specimens of Triebelina indopacifica are overall more worn, and marginal spines are less well preserved, although they have been illustrated on the type material ( van den Bold 1946: fig. 7). Four broken marginal spines occur along the antero-ventral margin of the smaller LV, and minute structures along the posteroventral margin ( Fig. 4).

Lateral normal pores

In all three Triebelina specimens, lateral NPC cross the entire thickness of the valve perpendicularly to the surface ( Figs 3H, I; 5H, I). They are not uniformly distributed, as they are closely associated with macro-ornamentation and less abundant in uniquely micro-ornamented zones ( Figs 3J; 4H; 5J). On the scans and 3D reconstructions, these macro-ornamentation related canals are rarely observed to cross the thickest portion of ornamentation features, while they are more abundant on the SEM images ( Figs 3A; 4A; 5A). These differential observations are, therefore, related to the resolution of the CT-scan, small pore canals being undetected. The following preliminary description consequently focuses on the largest pore canals clearly observable through scans.

Two rows of pore canals border the ventral ridge of all specimens and the median bulge in the case of T. indopacifica ( Figs 3J; 4H; 5J). Dorsally, they are also distributed into two rows along the horizontal ridge as well as the anterior and posterior lateral vertical elements. In areas lacking macro-ornamentation, pores are mainly located at the anterior and posterior ends of the lateral surface, where the crests and ventral ridge interrupt, but this pattern is strongly biased by the resolution limits of the CT-scan. The smallest LV of T. indopacifica displays numerous pore canals through the thickest parts of the macro-ornamentation, mainly through the posterior portion of the ventral ridge, while they are less numerous near the AMS ( Fig. 4H, I). Overall, a certain polarity of the distribution of canals for all the three valves studied is visible, with denser distribution along the ventral margin compared to the dorsal area.

The smaller LV of T. indopacifica displays a unique set of nine double pore systems aligned in two rows above the anterior termination of the ventral ridge ( Fig. 4 H-J). At the time of writing, we are not aware of any previous work reporting such systems of double pore canals in ostracods. These canals are relatively narrow, and they cross the valve thickness while being very closely positioned, nearly touching each other. The possibility that they may correspond to artifacts is precluded, as their respective walls are clear and coherent in axial, coronal and sagittal views. One anastomosed pore canal is also seen at the posterior end of the ventral ridge of the same LV ( Fig. 4I, K). Such unique pore systems, their relation to setae and calcification, and taxonomic significance should be appropriately investigated in the future. Overall, the area of the ventral ridge in T. indopacifica here appears as the richest in terms of diversity of pore canal morphologies.

The position of pores regarding reticulation is shown in Figs 3J; 4H; 5J. The reticulation at the surface of all macroornamental areas (dorsal, ventral and median ridges) is blurred and it is impossible to determine the relationship of pores to reticulation. In other areas, pores in all three Triebelina specimens are intramural. Further analysis of juvenile specimens will be of importance to compare the ontogeny of pore systems with the ontogenetic history of calcification. The study of complete carapaces will clarify how pore canals are organized in the two valves of these highly asymmetrical ostracods, if the asymmetry of the valves also corresponds to an asymmetry of the pore systems.