Bryozoans and Hydroids Workshop Day 5

Deadly beauty! How do stingers work? What are the advantages of being a colonial animal?

Why do most hydroids look like feathery plants while byozoans look like encrusting layers? We learn more about these fascinating animals during the last day of the Bryozoans and Hydroids Workshop.


Prof Ryland taught us more about hydroids today, highlighting how to tell apart the different kinds of feathery hydroids. Often, our job can be complicated by having one kind of feathery hydroid growing on another larger feathery hydroid.

I've often wondered with the bulbous things are on feathery hydroids. These are reproductive structures that are important in helping us figure out the species of the hydroids.

Each hydroid colony is usually all female or all male. The male reproductive structures contain sperm and are usually white, while the females have pink, yellow or orange structures (eggs or yolk).

Here's an example of a rare hermaphroditic hydroid (photo on the left), with smaller male reproductive structures below and larger female blobs above.

Some hydroids contain their eggs or sperm in complicated elongated baskets instead of smaller capsules.

Here's a variety of other shapes that reproductive structures can take. These are often tiny and can't be seen in the field. This is why we need to take specimens back to the lab. These have to be carefully prepared so that the important features can be viewed under powerful microscopes.

Prof Ryland tells us more about the fascinating life cycle of hydroids. Just like bryozoans, hydroids are zombies too. A feeding polyp may die out and a new polyp develop within the same 'cup'!

Prof Ryland also pointed out how animals that capture food with stinging tentacles often angle their tentacle in the same way, some up and some down, to maximise the area of coverage.

All cnidarians have cnidae or stingers. These include jellyfish, corals, sea anemones and hydroids. Stingers are amazing constructs! The fastest action in the animal kingdom that can punch through crustacea skeleton like a bullet. Read more about how stingers are fast and powerful like bullets. And check out this awesome video clip with an animation of how a stinger works.

Prof Ryland spent some time explaining more about the challenges facing colonial animals. One challenge is to pack the most number of animals in a small area. It turns out a hexagonal arrangement is the best. This explains much of the patterns of bryozoan colonies. Nature is not wasteful and some of the solutions found in nature can help us in applications such as designing office workstations, engineering storage tanks and lots more.

While bryozoans gather food from the water by creating a tiny current with their 'hairy' tentacles, hydroids don't do this and simply place a net of stinging tentacles across an existing water current. This is why hydroids tend to look more like feathery plants and many may orientated in one plane at right angles to a current. Bryozoans, on the other hand, are often in flat layer.

Being in a colony allows animals to be small, yet gather enough food to allow expansion by having more zooids. Studies show larger colonies have smaller zooids. Being in a colony means zooids can also specialise: some only feeding, while others have defensive or reproductive functions. This means all the zooids have to be able to share food as well as communicate with one another. These challenges and solutions reminds me of humans in a social grouping!

My day began with a wonderful surprise. This magnificent booklet on Coral Reefs of Singapore by Jolene Wong and Dr Sin Tsai Min of the Tropical Marine Science Institute. My thanks to Dr Sin for providing me some copies of this booklet. I'll be giving them out to schools and other organisations where I give talks, for their library

Today, I went via the Pasir Panjang Ferry Terminal, which is right next to the massive reclamation to create a new Pasir Panjang Container Terminal.

It's been a frenzy of non-stop field trips, amazing lectures and lots of interesting conversations and ideas. Exhilarating but exhausting. Tomorrow one more trip to the shores, to guide at Chek Jawa with the Naked Hermit Crabs!