Why are brittlestar arms so long?

Marine biologist Matt Doggett answers your wild question. 

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A brittlestar, known scientifically as Ophiothrix fragilis

A brittlestar, known scientifically as Ophiothrix fragilis, photographed at Kimmeridge, Dorset © Paul Kay / Getty

 

Brittlestars belong to the class Ophiuroidea, a word derived from the ancient Greek for ‘snake tails’, which aptly describes the serpent-like movement of their long, flexible arms.

Brittlestars use these appendages in a whip-like manner to crawl quickly across the seabed – far more quickly than the typical seastar.

It’s an important adaptation, since many brittlestars are scavengers, feeding on detritus. The faster they can move, the more likely they are to get to the food first.

In the UK the colourful Ophiothrix fragilis (pictured), known to cluster in dense carpets on the seabed, uses its arms to feed as well as move, raising them in the water column to capture food passing on the current. Perhaps those with the longest limbs are able to catch more. 

Brittlestars are found in a variety of marine habitats, from rockpools to the deep sea. Some species bury themselves in mud or hide in crevices, while others climb onto corals and sponges.

The arms of some species can reach over 60cm. The UK’s largest species, Asteronyx loveni, inhabits deep waters and has arms up to 35cm long. 

 

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