Zooming in on Zoanthids

Serina Rahman is the co-founder of Kelab Alami and a Visiting Fellow at the ISEAS-Yusof Ishak Institute, Singapore

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Sometimes you see them carpeting the entire shorelines of rock and rubble which looks like thousands of little jelly-like flowers. Zoanthids are Cnidarians and belong to the same group as jellyfish and corals. They are more closely related to anemones, except that they live in colonies or big groups (like corals do).

Sometimes zoanthids look like coral polyps in the way they pack live so closely with each other, but the difference between them is that corals have a hard skeleton – zoanthids don’t. At the most they seem to be connected to each other through a soft rubbery mat of tissue. Zoanthids also often have 2 rings of tentacles, which differentiates them from other similar-looking animals.

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“zoanthids feeding”: When completely covered with water, zoanthids open fully with tentacles extended to catch their prey

At the low tide, zoanthids retract their tentacles and close their polyps tight to retain moisture. When the water returns, they open up and begin feeding again, and their tentacles can be seen waving in the waves to catch their planktonic prey. Similar to corals, some zoanthids have zooxanthellae (symbiotic algae) that live within them. These ‘zoox’ photosynthesise also provide nutrients to the zoanthid.

“retracted”: When it is low tide, zoanthids retract their tentacles and shut themselves tightly to retain moisture until the high tide returns

Squishing zoanthids during inter-tidal walks not only hurts or kills the animals but can also be dangerous to the human squisher! Some species contain powerful toxins, such as palytoxin which can have severe consequences on human health, especially if handled with an open wound.

Kelab Alami conducts guided habitat tours that will allow you to safely observe zoanthids in their natural habitat. Log on to kelabalami.weebly.com for more information.


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