Critter of the Week: Flabellum (the dentures of the sea)

This fan-shaped beauty is large and solitary, with a widespread distribution throughout New Zealand and mainly lives on soft substrate in a broad range of depths (0 – 3200 metres).

Its name, Flabellum, derives from the Latin word flabellum, meaning “fan” due to the shape of its corallum (or calcareous skeleton), which makes them very distinct from other types of stony or scleractinian corals. They are also exclusively azooxanthellate – instead of housing symbiotic algae like zooxanthellate shallow water corals (the type you would see when snorkelling on the Great Barrier Reef or in the Pacific Islands!), they feed on plankton, detritus and dissolved nutrients. Most of New Zealand’s corals are actually azooxanthellate (110 species) compared with their zooxanthellate relatives (17 species) which are all found in the Kermadec Islands

Polyps of Flabellum burst in colours of neon green, pink and red which makes the coral quite a sight to see live as you will see in the images below.

Here is a shallow-water Flabellum collected at 205 m from the Bay of Islands in 2009. There are currently nine species of Flabellum known from the New Zealand region. From this photo, you can see the vulnerable, bright-coloured polyps protected within the calcareous, partitioned inner framework of the Flabellum. Imagine swapping this Flabellum with your grandmother’s false teeth to give her a good fright in the morning. [Peter Marriott, NIWA]

An image from NIWA’s Deep-Towed Imaging System which shows the lonely, solitary life of this Flabellum found at 500 m in the Chatham Rise, east of New Zealand. [NIWA]
Yellow arrows point to a few solitary deep-sea caryophyllid cup corals found in the Graveyard Seamounts, located in the Chatham Rise at 800 m in depth. Unlike Flabellum, they usually attach to hard substrate and are limited to continental margins and seamounts. [NIWA]
A different species of Flabellum from the Ross Sea, Antarctica which has settled on a gravelly substrate with shell hash and a few common Antarctic brittlestars. Flabellum are environmentally tolerant which is why they are widely distributed, allowing them to inhabit extremely cold environments like Antarctic waters. [NIWA]

Further information

This website (Tree of Life) has some great information about flabellids