Bryozoans and Hydroids Workshop Day 3

Today, we learn more about hydroids. As it's a public holiday, there is a large turnout of volunteers for the afternoon lectures and lab at St John's Island.

What are hydroids? How do we find them? We learn these and more about these quirky creatures on Day 3 of the Bryozoans and Hydroids Workshop.


Dr Serena Teo introduces Emeritus Prof John S. Ryland, a great authority on a wide range of invertebrates. We are very lucky to have the opportunity to learn from him.

Prof Ryland patiently explains some of the fascinating history of studying invertebrates and hydroids. Often mistaken for plants, hydroids are animals and some can pack a powerful sting!

Although in the past, they were said to undergo alternation of generations, today we recognise them as having a complicated life cycle. Going through a stage when they are stuck to a hard surface, to a stage when they look like a jellyfish and swim about freely. The jellyfish stage is considered the adult stage, because this is when the animal produces eggs and sperm, from which tiny free-living larvae develop. The larvae eventually settle down to the immobile stage. Of course, there are many variations of this life style.

In some hydroids, the immobile form doesn't produce jellyfish adults. Instead, this stage is reduced to eggs or sperm which are contained in a special zooid with a shape that is often different from the feeding zooids (kind of like bryozoans!). These sexy capsules help identify the hydroids, so it's a little difficult identifying non-reproducing hydroids.

Hydroids are differentiated mainly between those that have a 'cup' into which the tentacles can retract. And those that don't have a cup.

Like bryozoans, hydroids are colonial and made up of zooids. The individual zooids bud off in ways that give rise to distinctive colony shapes. Hydroids may resemble feathers, bushes and their branching patterns often resemble plant forms.

Hydroids without 'cups' can have wonderful shapes and arrangements of tentacles.

Prof Ryland shares lots of photos of what hydroids look like and where we might find them.

Some may be overlooked when they are out of water.

There are all kinds of hydroids on seaweeds like Sargassum!

And to make life complicated, there are often smaller hydroids growing on larger hydroids!

There are also hydroids that grow only on snail shells occupied by hermit crabs! This is just some of what Prof Ryland shared during the lecture.

After the illuminating lecture, Prof Ryland shares more about hydroids in the lab.

We go through some of the hydroids collected recently during the field trips. The tricky part was trying to find the sexy bits that help identify the hydroids. The zooids of these animals are so tiny!

Prof Ryland has kindly provided reference materials which are immediately read during the lab to try to identify the many samples of hydroids.

Meanwhile, Dr Dennis is taking a closer look at all the specimens we found earlier in the morning. Here's a little pond of our freshwater samples!

Dr Dennis also continues to patiently share more on how to identify bryozoans.

With the help of Pei Yan and Phillip, Kwan Siong is performing a delicate operation.

Kwan Siong is carefully shaving off the bryozoans from the planks we found in the morning.

Here's Dr Dennis' notes of the various bryozoans we found in the mangroves and freshwater this morning. Wow!

Tomorrow, is the last day of the Workshop and there are no more field trips. I'm exhausted but sad that it's coming to an end so soon. We sure got a lot done in a very short time!