On sponges and spicules with Magdalena Łukowiak

When speaking of paleontology, people usually think of large bones and sharp teeth of fearsome dinosaurs. Needless to say, real paleontology is much more than just jaws and bones of dinosaurs.

Magdalena Łukowiak (*5 March 1984) is a Polish paleontologist affiliated with the Institute of Paleobiology of the Polish Academy of Sciences. She works on microfossils which means that she spends most of her time looking into the microscope. Magdalena is doing research on sponges, primitive multicellular organisms that are distributed worldwide and live mostly in quiet and clear waters. More precisely, she works on the structural elements that provide the support to their bodies and discourage the predators. These elements are called the spicules.

Daniel Madzia: Tell us more about the spicules.
Magdalena Łukowiak: Spicules are an analog of bones. They make the sponge body more stiff and resistant. Most of the sponges are equipped with a set of spicules. In some sponge groups the spicules are made of calcium carbonate, in others they are siliceous, or even made of organic matter. Every sponge species possess a definite set of spicules of different shapes. Some sponges have spicules of only one very general and simple shape; others have a few different types. In some cases, the spicules are of such a characteristic appearance, that you can determine to what species they belong.

DM: How are they formed?
MŁ: They are usually formed in special cells called the scleroblasts. If the spicules grow too big to fit inside the cell, they are transported out of the scleroblasts and their growth continues. Then they are moved (by other special cells) to a place in the sponge body where they are needed.

This fascinating mechanism of spicule formation and transport is recently considered by scientists to be used in technological innovation. Engineers have long been dreaming of structures which could be programmed to mount themselves.

DM: How did you get to sponges in general and sponge spicules in particular?
MŁ: I was initially working on the skeletal elements of fossil crinoids. I completed my Bachelor’s and Master’s degrees studying these echinoderms. Then, I was offered to switch to sponges and investigate their skeletal elements – the spicules. As I had been already working on marine organisms, I thought that sponges – being some of the most primitive known animals – must also be very interesting to do research on. And I sincerely hope that my studies will shed some light on their history. Sponges are currently among the most intensively studied organisms on Earth.

DM: Why is that?
MŁ: Well, the knowledge of them is still relatively poor even though they can be found in almost every marine environment; all the oceans and seas – from deep polar waters, through hydrothermal vents, to shallow water coral reefs. Of course, they live in fresh water environments too. And also it’s because of the secondary metabolites they produce. That makes them popular objects of study in the pharmaceutical industry. Nevertheless, our knowledge of these primitive multicellular organisms and their geological past is still poor.

DM: That’s interesting. How are the sponges used in pharmacy?
MŁ: It turned out that the chemicals they produce to defend themselves against the predators and other sponges (competing for space) have antiviral and antifungal properties. They were used to create pharmaceuticals for treating herpes and even HIV. Other metabolites, such as fatty acids, are used to treat different types of cancer.

DM: Let’s get back to the spicules. What can they tell us about the sponges?
MŁ: After a sponge dies, the spicules that were inside its body become incorporated into the sediment. They can be preserved and extracted from these deposits even after hundreds of millions of years. So, the spicules prove that sponges lived in that area. If we are lucky, we can identify the groups (and in some cases even species) based on the spicules. Knowing the depths and conditions that particular sponges prefer, we can also reconstruct the environment they lived in.

It’s also possible to reconstruct the history of sponges based on their spicules. When we find spicules that are typical for particular sponge species, living today in a certain place, but the material comes from a completely different part of the world, the fossil record gives us important information regarding their past migrations.

DM: You also studied the spicules of sea squirts (ascidians). How do they differ from the spicules of sponges? Can they be distinguished easily?
MŁ: Ascidian spicules are of the same size so at the first glance they are not easily distinguishable from some stellate types of sponge spicules. But when you look more carefully, you notice that they are more milky in their color (unaltered sponge spicules are transparent). They can be made of calcite or aragonite, but they can also be siliceous, vaterite, or made of amorphous fluorite and other minerals. As in the case of sponges, ascidian spicules are formed in their body. However, in contrast to sponges, the spicules of sea squirts are situated only in certain body parts, for example in the guts. As the spicules of sponges, the ascidian spicules have a taxonomic potential too (we can often say what groups of ascidians they belong to). But their variability is much lower than in sponge spicules.

DM: Alright! The last question – what’s your favorite sponge and why? 🙂
MŁ: I really like the carnivorous sponges! I would want to see them in their natural environment. Not just because they feed in a very different way the most sponges do (sponges are usually filter feeders) but also due to their appearance. They just look like out of this world. Consider the lyre sponge (Chondrocladia lyra) – it looks like an underwater chandelier. And Chondrocladia lampadiglobus is called the ping pong tree sponge because of its ping-pong-ball-shaped projections.

Featured image © Thierry Perez.
Picture of the sponge spicules © Magdalena Łukowiak.
Photo of the lyre sponge © Lonny Lundsten, Monterey Bay Aquarium Research Institute.

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