Critter of the Week: the beautiful group of marine snails - Calliostomatidae
New Zealand marine molluscs are incredibly diverse, with nearly 3,600 species described or known undescribed (Gordon, 2009).
What is even more amazing, considering the entire New Zealand mollusc fauna (marine, freshwater and terrestrial), 85.1% are considered endemic! While this is particularly high, compared to other groups we have studied, New Zealand’s fauna (and flora) generally has a large proportion of endemism (http://en.wikipedia.org/wiki/Endemism) owing to its long geological isolation and great geographical separation from other landmasses.
This week, we want to highlight a beautiful group of marine snails, the Calliostomatidae. About 300 species are known worldwide, they occur from the intertidal to the deep sea (to about 3000m depth) and are considered carnivores. This group is particularly well-represented in New Zealand with 39 species known in the region, including some of the world’s largest (Calliostoma tigris can reach more than 10cm in shell height).
Many of these species are beautifully ornate and beaded, some of them are distinctly shiny and smooth. Take a look at the Te Papa online mollusc collection that shows some of the beautiful range of shapes and sizes. Note that the name and date following the species name refers to the original description. Most of the species have been described by our most prominent New Zealand malacologists (mollusc experts) Richard Dell (+2002) and Bruce Marshall (both at Te Papa):
For another informative site on New Zealand molluscs, check out mollusca.co.nz with lovely photos, maps and species information.
Calliostoma selectum in comparison is much larger than C. alertae in previous image, collected in 190 m depth west of Chatham Islands. Endemic to New Zealand and frequent all around the islands, from 20 to hundreds of meters.
There is always so little we know about the ecology and behaviour of these animals that any of this information is exciting: apparently this species feeds on tube-dwelling polychaetes and hydroids (according to Steve de C. Cook’s ‘Coastal Marine Invertebrates’ book). [Ocean Survey 2020 voyage TAN0705]
A small shiny beacon perched on the bit of hard substrate it could find on the southwestern Chatham Rise (651m). The perch is probably not a rock but a Xenophyophore (http://en.wikipedia.org/wiki/Xenophyophore) a weird group of giant deep-sea foraminiferans.
Credit: DTIS/ Ocean Survey 2020 voyage TAN0705
A paper by Holmes, Duncan & Schnabel (2010 in the journal Molluscan Research) reported some behavioural observations that may go some way to explaining why the calliostomid shells are often to beautifully shiny. Specimens of C. alertae were collected on the Challenger Plateau Ocean Survey 2020 voyage in 2007 (see also specimen image above) and kept alive in a seawater tank. A peculiar behaviour called ‘shell wiping’ was observed, at least once every 24 hours. The snail extends its foot and sweeps it up and along the outside of the shell, a process that took about an hour. The authors hypothesise that this behaviour functions to reduce shell fouling but may also provide extra food particles. The image shows a compilation of images representing the sequential steps of the shell-wiping process as published in the paper.