Jun. 05, 2012

Daisy Brittle Star

by Coastal Studies for Girls

Click to enlarge images
by Dana, 10th Grade, Coastal Studies for Girls
 
Recently at Coastal Studies for Girls, we had the chance to visit the Bowdoin College Marine Lab in Maine where we observed some very interesting marine wildlife. One species that caught my attention from the start was the brittle star (Ophiopholis aculeata). The brittle star is like a starfish, but with slender and delicate arms that have a rough, bumpy texture to them and a tendency to break off quite easily.
 
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When I saw a brittle star lose its arm, it scared me and left me thinking that I may have hurt or permanently damaged the brittle star. As it turns out, this was a defensive strategy and the brittle star would ultimately be fine.
 
I wanted to know more about this star and how it can live with such delicate arms. One thing that I found out is that the breaking off of the brittle star's arms can confuse predators and give the brittle star a chance to get away from the danger it may be facing.
 
The brittle star tends to eat bits of decaying matter and microscopic organisms that can be scraped off the rock it is inhabiting.  It also occasionally feeds on tiny arthropods such as polychaete worms or small crustaceans. Brittle stars are not like most sea stars when it comes to taking in and digesting food. Most sea stars extrude their stomachs to feed, but the brittle star cannot. The brittle star’s food is taken in to the mouth, through the stomach and absorbed along the alimentary canal as it has no intestines or anus. The waste then goes back out of the mouth.
 
I also wanted to satisfy my curiosity about how the brittle star is able to breathe underwater without needing to resurface to get oxygen from the air. Brittle stars do not have lungs like we do, but instead they have ten bursae, which are cilia-lined sacs through which gas exchange and excretion occur. The ten bursae are found on the underside of the brittle star, where water can flow through them and the oxygen can be extracted. The oxygen is then transported through a series of vessels and sinuses throughout the brittle star.
 
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