Three kinds of spiral-shelled nautilus have been identified as separate species, increasing the known number of nautilus species by as much as 50 per cent.
Hundreds of millions of years ago, these relatives of octopus and squid were far more diverse, with thousands of species known from fossils. But today, only about six species live on the deep slopes of coral reefs around Indonesia and parts of the western Pacific Ocean. The precise number of living nautilus species has remained unsettled among researchers.
鈥淸Nautiluses] inhabit ecosystems just a stone鈥檚 throw away from the coast and humans, yet we know next to nothing about them or their habitat,鈥� says at Central Campus, Des Moines Public Schools in Iowa.
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Many populations that haven鈥檛 been well-studied 鈥� such as those found near South Pacific islands 鈥� have traditionally been considered part of the wide-ranging Nautilus pompilius, says Barord.
But on nautilus genetics suggested that the spiralled swimmers found in Fiji, Vanuatu and Samoa were evolutionarily distinct from other nautiluses and possibly from each other.
Barord and his colleagues examined shells from museum specimens and recently collected animals found near the islands, comparing their shape, colour and patterning with nautiluses from elsewhere. They found that each population鈥檚 physical features were distinct, and formally named and described them as three separate species.
Nautilus samoaensis from Samoa has a branching pattern to its dark orange shell stripes not found in other species. Nautilus vitiensis from Fiji is relatively small and has very little striping on its white shell. In contrast, Nautilus听惫补苍耻补迟耻别苍蝉颈蝉 from Vanuatu has much of its shell covered in thick, dark stripes.
The gas-filled chambers of a nautilus shell implode below 800 metres deep, and nautiluses don鈥檛 tolerate the warm surface waters in the tropics. These factors might work together to keep the animals stuck around the underwater slopes near these islands, causing populations to differentiate from each other over time. Barord thinks there are probably other undescribed, endemic nautilus species on similar island chains.
Modern nautiluses鈥� outward appearance is similar to their ancient relatives and they have thus been commonly termed 鈥�living fossils鈥�. Barord isn鈥檛 a fan of the characterisation.
鈥淭he term 鈥榣iving fossils鈥� just does not give enough credit to how different populations of nautiluses adapted to their changing environment,鈥� he says.
at James Cook University in Australia points out that there is a market for nautiluses鈥� beautiful shells. Since nautiluses don鈥檛 breed until about 15 years of age, she says, nautilus populations are especially vulnerable to extinction from being harvested by humans.
Naming and describing these unique species can help focus efforts for their protection, management and conservation, says Strugnell. The identification of key shell features for each species is useful too, she says.
鈥淪hells that have been purchased or are for sale might be able to be assigned back to their species or location of collection, and provide some more information about these species,鈥� she says.
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