More than just pretty shells: AMRI researchers study diverse family of gastropods

Volutes are a family of shelled molluscs, comprising some of the largest of all gastropods. They are, arguably, more diverse and spectacular in Australia than anywhere else. However, much remains unknown about this enigmatic family. AMRI researchers are now addressing this knowledge gap by conducting the largest study on volutes to date.

At some point around the middle of the eighteenth century, one of the most celebrated naturalists of all time – Carl von Linnaeus – inspected a seashell. Having devised a binomial system to name Earth’s multitude of life forms, yet to be published in his famous work Systema Naturae in 1758, he needed two names – one for genus and one for species. Holding the shell up to the light, he would have noticed its intricate, mysterious pattern – one almost appearing more hieroglyphic than natural, with its numerous motifs of lines and curves, dots and rectangles. The name he chose, Voluta musica, perfectly captured the nature of the object before him – its fine, repetitious pattern appeared as sheet music. Although, one not penned by humans, but meticulously adorned by the animal inside the shell.

In the early years of the following century, the Australian volute Amoria undulata was named in a similar fashion, its name describing an undulating and remarkably symmetrical shell pattern. Later, another naturalist named a species Ericusa fulgetrum, the latter word Latin for lightning. It would seem that already centuries ago, volutes held an intriguing power in their manifold, striking markings. Add to those their often large, glossy shells, and it would not take long before they became eminently collectible, highly coveted items.

In the latter half of the 20th century, a man of extraordinary wealth and notoriety – the American John du Pont – was also captivated by these remarkable seashells. Back then, one of the rarest of all volutes was Cymbiola perplicata – a species so scarce that it was known from only three specimens, all purchased in Cairns in 1901 by the Australian Museum curator Charles Hedley. In the nearly seven decades to follow, no more examples of this intriguing species had surfaced, something du Pont was determined to rectify. In 1968, he mounted an audacious expedition along the coast of Queensland in search of C. perplicata – such was the allure this rare shell held to him. Alas, he returned from the endeavour empty-handed.

Australia hosts about a quarter of the world’s volute diversity, several of which are considered among the most exquisite of them all. However, there is more to volutes than their impressive shells; because their larvae typically cannot swim, but rather settle directly on the seafloor immediately after hatching, they are unable to effectively disperse. Subsequently, they readily become genetically isolated, resulting in restricted distributions and, typically, a high degree of endemism. For example, in Australia, most genera and nearly all species occur only here. As such, they form a unique and important part of our shared natural history.

Volutes are part of the order Neogastropoda, a remarkably diverse group of predatory molluscs that includes well-known families commonly known as cone snails, murex, whelks and auger shells. In recent years, many of these have become increasingly well understood in terms of their systematics, anatomy, diet, and, in some cases, their venom. However, this is not the case for volutes – remaining comparatively poorly known in terms of their evolution, most of their classification is derived from their shells. Relatively few species have been studied anatomically, and only a handful feature in genetic studies. That is, until now.

Researchers at the Australian Museum Research Institute are now conducting a major study on this fascinating family. Integrating phylogenomics (the study of how different groups relate to each other using whole or partial genomes), shell morphology and fossil history, the aim is to better understand their evolutionary relationships and to improve their classification. A particular focus will be given to Australian groups, where study will also be dedicated to better understanding species and subspecies boundaries, their morphological features (including their radulae, or ‘teeth’), as well as geographical distributions.

This is important for several reasons; firstly, the restricted distributions of many volutes render them vulnerable to conservation issues resulting from ocean acidification and other challenges relating to climate change, habitat degradation, and in some cases, overharvesting. Improved knowledge of species boundaries and distributions will enable targeted conservation measures. Enhanced systematics will facilitate study relating to their toxins and other features, as particular lineages of special interest can be more confidently identified. This will also help elucidate how the family has diversified, in turn contributing to the growing body of evidence regarding how neogastropods – the order to which volutes belong – have become so diverse and successful in evolutionary terms.

With this study, we aim to look beyond the pretty shells of volutes and arrive at new insights about the evolution of this compelling family of gastropods. Yet, their intricate patterns may remain undeciphered – for now.

Authors:

Anders Hallan, Research Associate, AMRI

Ian Mattiske, Research Associate, AMRI

Frank Köhler, Senior Principal Research Associate, AMRI