More mind-boggling hydroids are revealed by Emeritus Prof John S. Ryland on Day 4 of the
Bryozoans and Hydroids Workshop.
In the jellyfish stage of this hydroid, the animal does not swim about freely, but 'walks' about on its 'legs'. It can capture small crustaceans! When I learn more about our invertebrates, it's like exploring an alien planet!
Today, Prof Ryland systematically went through the different groups of hydroids, covering a vast array of these creatures that may look similar but are very different when we take a closer look. Here, I'm just highlighting some of those that I found interesting. Prof covered a lot more in his talk. This freshwater hydroid is the 'typical' hydroid familiar to many biology students as it is often used in student laboratory work.
But hydroids can take bewildering forms. Some hydroids look like hard corals. Because they pack a powerful sting, they are sometimes called fire corals. They can be quite colourful. Some belong to Family Stylasteridae.
Another kind of stinging coral-like hydroid belong to Family Milleporidae. They have two kinds of polyps that emerge from a stony structure. One is a feeding polyp surrounded by a ring of stinging polyps studded with stingers.
Some hydroids look like sea fans! Another reason why we should not go around touching marine life with our bare hands.
While the majority of hydroids are colonies, some like this one a solitary polyp and a large one too! Chay Hoon has seen these in our waters.
And here's a strange animal that I've not seen on our shores before. This is a hydroid (Prof says they don't sting) that floats in the open sea (pelagic). It can be considered a 'upside down' version of a colony of encrusting hydroids and not really a jellyfish. It has a slanty 'sail' on the top of its hardened circular body. In some the sail is slanted to the left, others to the right. They go wherever the wind blows them, and often, large numbers may wash up on the beach. This is often a bad sign as more dangerous animals like the Portuguese-man-of-war may wash up at the same time.
Here's a video clip about a bloom of these animals, in a charming Mediterranean accent.
I also recognised some of our familiar hydroids. This one can be abundant especially on our Northern shores. I call them
fluffy hydroids.
And here's a closer look at the transparent fern-like
hydroids that sting powerfully. I've been stung by these and they feel like a jolt of electricity.
And here's some hydroids that emerge from long tubes.
Are these the same as the
delicate feathery animals on our shores which I think are hydroids. Must find an opportunity to confirm this.
There are also hydroids that settle on shells of living snails, or on shells occupied by hermit crabs.
I think hydroids are what were covering this snail that I saw at Changi East in 2011!
In this one, the tiny hydroids had completely covered the shell occupied by the much larger hermit crab. Each colony of hydroids is usually either male or female. A colony that has eggs is either pink or yellow (yolky) while a colony that is male has white sperm-filled sacs.
Some kinds of hydroids have a little cup into which the animal with tentacles can withdraw. This cup may be closed with a tiny door or operculum. Hydroids also have different kinds of reproductive capsules in which the jellyfish stage are produced. In some the jellyfish adults are released, each animal either male or female, and reproducing away from the immobile hydroid. In others, the jellyfish stage may remain attached to the hydroid, with each jellyfish also producing eggs and sperm so that egg fertilisation takes place on the hydroid. In others, the jellyfish stage is so reduced, the capsule only contains eggs or sperm.
The shape and features of these reproductive capsules and the adult jellyfish help to distinguish the species. So it's difficult to identify hydroids which are not in reproductive state. Also, much work has to be done to learn about the entire lifecycle of the animal: either rearing hydroids to release adults, or adults that eventually produce larvae that settle to produce the hydroid.
Some hydroids don't have a cup-shaped thing to hide in. These can be divided into those with skinny tentacles without knobs at the tips, and those with some or all tentacles with knobs at the tips. These look like Sundew plants to me!
In most hydroids, the jellyfish stage is very small. In
Aequorea, however, the jellyfish stage is quite large. We have seen these in our waters. To be correct, these are not true jellyfishes, many of which belong to
Class Scyphozoa.
To make life super complicated for those trying to identify hydroids, there are often tiny hydroids living on larger hydroids!! The cup-shaped bits are one hydroid living on a larger feathery hydroid which has tiny polyps.
Today Prof Ryland also shared more tips about how to preserve and create good specimens of hydroids for study. Many of these methods are lost and only older people like Prof knows all the short cuts and tricks learnt from years of work. Properly preserved and stained, these beautiful specimens can last for many years in natural history museums for current and future study.
We didn't have a field trip this morning because the low spring tides are over. But there was still a lowish tide when we arrived at St. John's Island. Sigh. I still get the itch to go out and have a look even though I've been out every day for 6 days in a row already!
Fortunately, we are never far from marine life at TMSI. There is a lovely touch pool near the meeting room where we can get a real close look at live animals. And the Giant clam in the pool was particularly lively today, squirting us several times!
Besides the Giant clam, in the touch pool today there was a little biscuit sea star, several different kinds of hard and soft corals, as well as colonial anemones and corallimorphs.
In between, there's all kinds of bryozoan excitement going on in the lab. Rene shows me some sperm in a bryozoan, but I couldn't photograph them from the microscope. Dr Dennis shows me the feeding animals in a bryozoan we
found yesterday in large numbers in the mangroves at Lim Chu Kang. They are large enough for me to take with small sneaky cam.
Thanks to Dr Serena Teo and Heng Jiarui of TMSI, I'm catching a ride to catch the last day of lectures tomorrow.
