EXBODI / A «sea» of Brachiopods
27 September 2011
Among the strange creatures encountered during this oceanographic cruise, we need to talk about the great abundance of Brachiopods in some banks of the New Caledonian EEZ.
Brachiopods nowadays are a very discreet group. Most of the species live attached to hard substrates by one of their two valves.
They appeared during the primary Era (Paleozoic), they were a very important component of marine organisms during the Mesozoic (secondary Era).
In the central area of these banks, that actually correspond to an old crater, the bottom is formed of consecutive layers of Brachiopods, as indicated by the dredge and trawl samples we brought back to the surface.
It could be a long stretch to compare this biotope to these long-time gone seas contemporary of dinosaurs but this zoological curiosity does raise questions. We can indeed wonder about environmental conditions that allowed the settlement of such Branchiopod populations.
Today, there are about 300 species, mostly found in Southern oceans. Several new species have recently been described from shallow and deep waters from New Caledonia.
What is a Branchiopod?
At first sight, it resembles a mollusks as it possesses two valves like bivalves. In contrast to bivalves which possess a right and a left valves, Brachiopods have a dorsal and a ventral valves that are not symmetrical. Inside, the shell houses an organ suspended to a skeletal part. This organ, called lophophore, has both a respiratory (like a gill) and a feeding (plankton filtration) function.
The phylogenetic position of this group, that appears in the fossil record as early as the early Cambrian, is very disputed. The most recent studies indicate that this group corresponds to a monophyletic lineage among the Lophotrochozoans.
Bitner, M. A. (2009). "Recent Brachiopoda from the Norfolk Ridge, New Caledonia, with description of four new species." Zootaxa 2235: 1-39.
Bitner, M. A. (2010). "Biodiversity of shallow-water brachiopods from New Caledonia, SW Pacific, with description of a new species." Scientia Marina 74(4): 643-657.
Hausdorf, B., M. Helmkampf, et al. (2010). "Phylogenetic relationships within the lophophorate lineages (Ectoprocta, Brachiopoda and Phoronida)." Molecular Phylogenetics and Evolution 55(3): 1121-1127.
Helmkampf, M., I. Bruchhaus, et al. (2008). "Phylogenomic analyses of lophophorates (brachiopods, phoronids and bryozoans) confirm the Lophotrochozoa concept." Proceedings of the Royal Society B: Biological Sciences 275(1645): 1927.
Sperling, E. A., D. Pisani, et al. (2011). "Molecular paleobiological insights into the origin of the Brachiopoda." Evolution & Development 13(3): 290-303.