Walters Shoal's marine fauna and flora - Some molluscs from the Walters Shoal!
About 200 species of molluscs were found to date in Walters Shoal, mainly gastropods and bivalves, 120 of which were alive and thus suitable for subsequent anatomical and genetic studies.
A high proportion of the molluscs we found are minute, such as the tiny Columbellidae shown in the picture, and could only be detected after meticulous sorting using binocular microscopes.
Some remarkable nudibranchs were retrieved from the samples collected by the divers in shallower waters; these shell-less and often vividly coloured gastropods live generally associated with corals or sponges, and are able to re-use the toxins produced by their prey for their own defence. Corals also host other gastropods that live and feed on them, including the pink Coralliophilinae Babelomurex lischkeanus shown in the picture, and the vermiform Aplacophorans that coil themselves around the branches of soft corals.
At least four different species of Eulimidae were collected, one at the summit of the seamount and three in deep waters. These gastropods are parasites living off different groups of Echinoderms such as the Ophiuridae or brittle sea stars as shown in the picture, which were in fact quite abundant in our samples. We also found some limpet-shaped tiny Lepetelloidea, a group of gastropods that inhabit biogenic substrates including whale bones, sharks’ eggs and wood: some living specimens were found on a sunken bird feather, a quite unusual substrate caught by a trawl at a depth of about 1000 m! Empty shells of Bathysciadium, another Lepetelloidea that lives on Cephalopods beaks, were collected in the shallow waters of the summit area. Another interesting catch is a species of Kaiparathina, a genus including only 5 described species from South Pacific that was collected dredging at a depth of 500-600 m.
Generally speaking, at the summit we found some gastropod species with planktonic larvae, able to disperse over long distances. Larval development type can be easily inferred from the shape of the larval shell that is retained at the tip of the adult shell. These species are known to inhabit the tropical Indian Ocean and appear to reach their distribution limit on Walters Shoal. In fact, most of the species that inhabit the summit area are very small and have a non-planktonic larval development, indicating a reduced ability to disperse. This characteristic suggests that they are endemic to Walters Shoal and thus new to science: there will be work for the taxonomists upon our return!
