Brittle star hitching a ride on a jellyfish

While waiting for the boat to arrive at the jetty of St John's Island after our trip this morning, I had a pleasant surprise!



I spotted this brittle star (Subclass Ophiuroidea) hitching a ride on the bell of the Ribbon jellyfishes (Chrysaora sp.). This is my first time seeing such a phenomenon.

Chris Mah of The Echinoblog also happened to have blogged about this just last week! He mentioned that it is not certain how does the brittle star got onto the jellyfish but probably it is possible that they settle as larvae.

He also gave two hypothesis for the reason behind such a hitch-riding of brittle stars.

1) Food and protection- Brittle stars and other critters live around the oral arms of the jellyfish to take advantage of their feeding. Since the jellyfish can pack powerful stings, this can give protection to the commensal.

2) Dispersal via 'rafting'- It has been suggested that only small brittle stars can hitch onto the jellyfish. So when they grow up, they will fall off. And in the process, this can also help the brittle stars to reach other locations that the jellyfish goes to.

Wouldn't the jellyfish sting the brittle star?

According to the reply of Sabine Stöhr, ophiuroid specialist at the comment section of Chris Mah's blog post, Brittle stars are slimy and perhaps can tolerate the stings. As to when they know when to jump ship, they probably reach a certain size at which they perhaps don't get enough benefits from being on the jelly anymore. Maybe they need to away from the jelly to spawn or their eggs would be eaten by the jelly. But that's just speculation.

Read more about this hitch riding activity in Chris Mah's post in detail. :)