Here shows a good variety of echinoderms. Within this Phylum, we usually associate the sea cucumbers, seastars, urchins and featherstars... Like most marine invertebrates, locomotion is generally very slow, particularly in the echinoderms.
Featherstars - this organism is more commonly found along the reef crest and slopes. This one here was found on a sandy shore, perhaps washed up during low tide. Most echinoderms possess a pentaradial symmetry which also means that each symmetric portion of the body can move independently. Look at how the individual arms are waving and transporting the featherstar across locations - each one giving an undulating movement and pushing the featherstar along the water.
Lovenia heart urchin - this individual here is my very first sighting of a heart urchin in Singapore! I can still remember how I met this little fella - I was photographing a nudibranch and all of a sudden, the sand beside the nudibranch moved and out came the urchin! What a pleasant surprise for me. Earlier during the semester, students in my class were prompted with this question - with so many spines, how does the urchin 'walk' without breaking its spines? Getting them to realise that 1) not all the spines are of uniform length and 2) not of uniform thickness (aka strength). Thus, we would expect the thicker and stronger spines support the body weight while the remaining spines act as enlarging body and protection. Looking at how this urchin moves, it reminds you of the 'rowing' motion. haha...
Astropecten seastar - sometimes as you walk along the sand bar, the first sign of a seastar would be the imprint of a star on the sand. That leads you to your seastar found buried 4-5cm below the substrate. Check out how this seastar goes back into its comfort zone by 'sinking' into the substrate.
Enjoy the videos! Next series: Slugs.
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