Category Archives: Current projects

Project NorHydro: a quest for hydroids in Norwegian waters

One of this year’s new projects at the Invertebrate collections is NorHydro – Norwegian Marine Benthic Hydrozoa.

Both stages in the typical life cycle of a hydroid (polyp and jellyfish) are represented in the logo of the project

Funded by the Norwegian Biodiversity Information Centre (Artsdatabanken), NorHydro will be dedicated to the study of the ubiquitous (but commonly overlooked) marine hydrozoans of Norway.

Some of the most conspicuous Norwegian hydroids are large colonies somewhat resembling branching trees. Many other animals and algae may grow on these colonies making them their home

Hydrozoans are an ecologically and economically important group of animals. With approximately 3800 described species –and probably many more to be discovered– they are the most diverse group of medusozoan cnidarians in terms of number of species and life cycle strategies. Some hydrozoans live all their lives as jellyfish in the water column (thus they are holoplanktonic), but the vast majority of the species either take the form of polyps permanently connected to the sea-floor (benthic) or are meroplanktonic (i.e. possessing both a benthic polyp and pelagic jellyfish stage). Most of the time, the benthic marine hydrozoans (also called hydroids) go unnoticed by the public, but at times they can grow massively on submerged structures, causing problems for aquaculture, fisheries, and navigation, or producing huge numbers of jellyfish that in turn have a great impact on the local marine environment.

Hydroids come in different sizes and shapes. Colonies living on the same substrate (like these members of Cuspidella, Sertularella, and Grammaria) do not necessarily resemble each other.

To get a better overview of which hydroid species are present in Norwegian waters, NorHydro will sample, record, chart, and DNA-barcode specimens occurring all along the Norwegian coasts. The project will rely on specimens deposited in museum collections as well as on constantly obtaining new live animals that will be identified and documented with photos before they are fixed in ethanol for DNA barcoding of CO1 and 16S sequences. Producing information on the morphology (how does it look) and the DNA sequences (the information within) of Norwegian hydroids is very important, because together these data will allow NorHydro to generate useful tools for the future identification of hydroids from all around the world.

Dredges, grabs, sledges, diving and simply taking them by hand are all valid sampling methods when it comes to marine benthic hydroids. The specimens are then sorted, identified, documented with images, processed for DNA barcoding, and finally incorporated to the museum’s collection for future reference.

Understanding hydroid diversity in Norway is not an easy task, but fortunately NorHydro is not alone in this quest: several partners in Norway and abroad will team up with our project, including NorBOL (the Norwegian Barcode of Life), NTNU University Museum, Norwegian Institute of Marine Research, ForBio Research School in Biosystematics, Natural History Museum of Geneva, University of the Balearic Islands, and the Institute of Oceanology of the Polish Academy of Sciences. NorHydro will also benefit from collaborations with the other four currently ongoing NBIC projects at the Invertebrate Collections of the museum (see an overiview of each of these projects here, in Norwegian), which we are sure will result in a lot of exciting discoveries in the near future.

One important goal of NorHydro is to present marine hydroids to all those not familiar with these amazing creatures. In order to do that, we will regularly write entries here on the blog, as well as posting updates in Facebook and in Twitter with the hashtag #NorHydro. The official info webpage for the project is available here in English, and here in Norwegian, so don’t forget to check it out!

-Luis

New year, new field work!

2019 will bring a lot of field work for us at the invertebrate collections – not only do we have our usual activity, but we will also have *FIVE* Norwegian Taxonomy Initiative projects (Artsprosjekt) running!

On a rather windy Tuesday in January, four of us – representing four of these projects – set out with R/V “Hans Brattstrøm”.

Four projects on the hunt for samples! Photo: A.H.S. Tandberg

Our main target for the day was actually not connected to any of the NTI-projects – we were hunting for the helmet jellyfish, Periphylla periphylla. We need fresh specimens that can be preserved in a nice way, so that they can be included in the upcoming new exhibits we are making for our freshly renovated museum. We were also collecting other “charismatic megafauna” that would be suitable for the new exhibits.

We have been getting Periphylla in most of our plankton samples since last summer, so when we decided this was a species we would like to show in our exhibits about the Norwegian Seas, we did not think it would be a big problem to get more.

This is a species that eats other plankton, so normally when we get it, we try to get rid of it as fast as possible; we want to keep the rest of the sample! But we should have known. Don’t ever say out loud you want a specific species – even something very common. Last November, we planned to look specifically for Periphylla, and we brought several extra people along just because of that. But not a single specimen came up in the samples – even when we tried where we “always” get them…

Lurefjorden is famous for being a hotspot for Periphylla – so the odds were in our favor! Map: K. Kongshavn

Wise from Novembers overconfident cruise, this time we planned to call to the lab IF we got anything to preserve. The Plankton-sample did not look too good for Periphylla: we only got a juvenile and some very small babies. So we cast the bottom-trawl out (the smallest and cutest trawl any of us have ever used!), and this sample brought us the jackpot! Several adult Periphylla, and a set of medium-sized ones as well! Back in out preparation-lab an entire size-range of the jelly is getting ready for our museum – be sure to look for it when you come visit us!

We of course wanted to maximize the output of our boat time– so in addition to Periphylla-hunting, we sampled for plankton (also to be used for the upcoming ForBio-course in zooplankton), tested the traps that NorAmph2 will be using to collect amphipods from the superfamily Lysianassoidea, checked the trawl catch carefully for nudibranchs (Sea Slugs of Southern Norway, SSSN) and benthic Hydrozoa (NorHydro), and used a triangular dredge to collect samples from shallow hard-bottom substrate that can be part of either SSSN or the upcoming projects NorHydro (“Norwegian marine benthic Hydrozoa”) or “Invertebrate fauna of marine rocky shallow-water habitats; species mapping and DNA barcoding” (Hardbunnsfauna).

The Hardbunnsfauna project was especially looking for Tunicates that we didn’t already have preserved in ethanol, as we want to start barcoding these once the project begins in earnest (last week of March). We also collected bryozoans, some small calcareous sponges, and (surprise, surprise!) polychaetes.

When it comes to hydrozoans, we were lucky to find several colonies of thecate hydroids from families Campanulariidae and Bougainvilliidae that represent some of the first records for NorHydro. Hydroid colonies growing on red and brown algae were particularly common and will provide a nice baseline against which diversity in other localities will be contrasted.

Different hydroid colonies growing on algae and rocks at the bottom of Lurefjorden. Photo: L. Martell

There were not a lot of sea slugs to be found on this day, but we did get a nice little Cuthona and a Onchidoris.

But what about the Amphipod-traps? Scavengers like Lysianassoidea need some time to realize that there is food around, and then they need to get to it. Our traps have one small opening in one end, but the nice smell of decomposing fish also comes out in the other end of the trap. We therefore normally leave traps out at least 24 hours (or even 48), and at this trip we only had the time to leave them for 7 hours. The collected result was therefore minimal – we even got most of the bait back up. However, knowing that we have a design we can deploy and retrieve from the vessel is very good, and we got to test how the technical details work. It was quite dark when we came to retrieve the traps, so we were very happy to see them! All in all not so bad!

We had a good day at sea, and it will be exciting to see some of our animals displayed in the new exhibits!


If you want to know more about our projects, we are all planning on blogging here as we progress. Additionally you can find more on the

-Anne Helene, Cessa, Luis & Katrine 

Door #23: A model in the making

The University Museum is being renovated and prepared for a grand new opening within 2019. The building has been put back in shape and looks great (more on that (in Norwegian), and images here), and we are now preparing new exhibits for everyone to enjoy.

As part of producing the new exhibits, we are working together with the excellent model-makers at 10 TONS in Copenhagen to be able to show large scale models of some of our beautiful friends. But how do we make a proper model of a small invertebrate? We want it to be a correct large-scale version of the animal we are portraying, not some half-good almost-look-alike…And if it happens to be strikingly beautiful as well, that is not a bad thing!

A gorgeous model of something too small to be observed properly with the naked eye; the zooxanthellae in the polyp of a coral. Read more here: http://www.10tons.dk/coralpolyp Photo: 10tons.dk

First of all, a 3-D computer model is made. At this stage, the guys at 10 tons work closely with us scientists to make sure that all details are correct – and we use a load of photos, films, SEM-photos and taxonomic drawings to make sure we have all things covered. Sometimes we even send them a specimen that they can scan. The models are passed back and fourth between the model-makers and the scientists, with indications of small corrections pointed out and performed until all parties are happy. You can be sure that the scientists have several minute details they want to change just a tiny little bit more, but we get there in the end…

Work in progress. Image: 10tons.dk

The next step is that the 3-D computer model is printed in the size that is going to be in the exhibits.

The printed out model is coated in a super-thin layer of wax to make it smooth, and then all the tiny details are added. Small notches in the epidermis or tiny plumose seta that have been separately made are added.

For a researcher who describes all the separate seta on the different mouthparts this is an amazing process to observe, and for everybody who later will see the model there can be an assurance that what you will see is actually how the species looks.

But this is not the end! The materials that have been used this far in the process will loose or change their colour when exposed to light. Therefore, a silicon mold (a “negative mold” or a cast of the outside of the model) is made from the finished first model. This mold is used to produce a new positive cast of polyurethane resin – and this is the model that will be shown in the exhibit. This material allows the model makers to add the right colour, translucence and texture to give the right look and feel of the finished product.

Here are a few of the scientific models, many more can be found here

 

Models are not made only of small animals – sometimes they are scaled 1:1, like this minke whale:

Balaenoptera acutorostrata, image 10tons.dk

Or *just a bit* bigger than what we could expect to find our in nature, like this crab (Cancer pagurus)

image: 10tons.dk

Here’s a video of how models are made – there are a few more videos here

We researchers are at the moment eagerly awaiting the models that will come to the University Museum – we have seen the 3-D models, and some of us have seen some photos of the models that are being made. We know that the models will look good, and we are looking forward to sharing them with everybody who comes to see the exhibits.

Now, what species will you be able to see models of, and in which exhibits will they be? That is for us to know now, and you to find out next year!

The holiday-season is a time for secrets to be kept, and this is one of those secrets. Come visit the University Museum when we reopen the building in autumn 2019 to see for yourself!

-Anne Helene

Would you like to know more about the process of making such models? This paper gives details and photos of a project 10 tons did with a paleontologist from the university of Lund in Sweden: Eriksson ME, Horn E (2017) Agnostus pisiformis – a half a billion-year old pea-shaped enigma. Earth-Science Reviews 173, 65-76. https://doi.org/10.1016/j.earscirev.2017.08.004

Door #18: The hypnotic adventure of the Norwegian jellyfish

The end of the year is always a crazy time full with work deadlines and holiday planning, but if one can find a few minutes in between last-minute shopping and gift-wrapping, the last days of December can also offer the opportunity to reflect on past and current experiences and what we have learned from them. It is also a special time for closure, so it feels natural that it coincides this year with the end of HYPNO, one of the projects of the Invertebrate collections funded by the Norwegian Taxonomy Initiative.

For the last three years, project HYPNO (Hydrozoan pelagic diversity in Norway) has been documenting and DNA-barcoding the diversity of hydromedusae and siphonophores in Norwegian waters. We have learned a lot about the distribution of these animals in the process, especially since we have come face to face (or rather face to tentacle) with more than 1100 specimens from all parts of the country.

Representative species of the groups within Hydrozoa that were the object of study of HYPNO (from left to right and top to bottom): Amphinema rugosum (Anthoathecata), Mitrocomella polydiademata (Leptothecata), Lensia conoidea (Siphonophorae Calycophorae), Agalma elegans (Siphonophorae Physonectae), Botrynema ellinorae (Trachymedusae), Bathykorus bouilloni (Narcomedusae). Pictures: Luis Martell and Aino Hosia.

Telling all these organisms apart was not always an easy task, but thanks to a combination of traditional taxonomy and genetic methods we have been able to identify more than 120 species, including several new records for Norway and a couple of species that had gone unnoticed to the world until today. The project was very successful in getting useful DNA sequences for the majority of these species, which will facilitate the identification of hydrozoans in the future, and that will be available for everybody to use through the online platform of the Barcoding of Life initiative. All the records gathered during the project will also be available to the public (through the interactive maps of Artskart) and a collection of specimens will be stored at the University Museum of Bergen as a reference for anyone interested.

A nice overview of some of the results of HYPNO as displayed in the webpage of BOLD systems.

Additionally, keep an eye open for HYPNO’s most striking results that can be found in several scientific articles (published and in various stages of preparation), and for the project’s last updates in social media.

Without a doubt, HYPNO owes much of its success to the combined efforts of all the individuals and institutions that have collaborated in the project in one stage or another. NorBOL, GooseAlien, NorAmph, and Arts- og naturtypekartlegging av Sognefjorden are only some of the projects with which HYPNO has shared samples, experiences, and field trips. Collecting the animals and curating the specimens and data would not have been possible without the help of the crew working in the research vessels that hosted us and the technical staff at the DNA lab and the invertebrate collections of the museum.

HYPNO included samples from all over Norway, but we particularly enjoyed our regular sampling trips in the amazing Western Norwegian coast. Pictures: Luis Martell, Joan J. Soto Àngel.

Many records for the project came from friends and colleagues working in other institutions and universities in Norway and abroad, all of whom were eager to share their knowledge and time with us in this hypnotic adventure of Norwegian jellyfish.

We had always a great time jelly-hunting in the sea! Pictures: Luis Martell, Joan J. Soto Àngel, Anne-Helene S. Tandberg.

HYPNO may now be coming to an end, but this doesn’t mean that our work on Norwegian hydrozoans is finished. On the contrary, the Invertebrate Collections have been granted a new project starting next year and focusing again on these fascinating animals. We hope that the new project NORHYDRO will be as rewarding as HYPNO, and we know it will be at least as fun: time flies by so quickly when jellyfish and good friends are involved!

-Luis Martell and Aino Hosia

 

Some suggested reading related to the project
Schuchert P, Hosia A, and Leclere L. 2017. Identification of the polyp stage of three leptomedusa species using DNA barcoding.

Martell L, Tandberg AHS, and Hosia A. 2018. The illusion of rarity in an epibenthic jellyfish: facts and artefacts in the distribution of Tesserogastria musculosa (Hydrozoa, Ptychogastriidae). Helgoland Marine Research 72(1):12.

Door #17: Sea bunnies of Norway?

Some years ago, in 2015, the internet was taken a storm by the sudden rise of the so-called sea bunnies. It all started with a video taken the year before by a SCUBA diver in Japan who filmed the little creatures crawling around the seabed:

The species seen in the video is called Jorunna parva, and are since then worldwide unofficially known by the adorable pet name ‘sea bunny’ as it has a ‘fur’ like exterior with tiny upright ‘ears’ and a fluffy tail like bunnies do. The ‘fur’ is actually created by bunches of tiny rods, called the caryophyllidia. The caryophyllidia are arranged around little knots that are often dark coloured, which create the illusion of black dots on the animals. The seemingly ears are the animals rhinophores, that function as chemical receptors that make the animal able to detect its environment in search of food and other sea bunnies. Its tail on the back are actually its gills to extract oxygen molecules from the surrounding water, the ‘fluffier’ it is, the bigger the surface area, the easier it is to diffuse oxygen from the water. This sea bunny is small, often less than 2.5 cm, and can be found throughout the Indo-Pacific; from South Africa to Central Pacific. They have, like many sea slugs do, a high degree of colour polymorphism in the species, with colours varying from white with black dots, to yellow and even bright orange:

Different colours of Jorunna parva, aka the sea bunny (photo credits on image)

Unfortunately, our sea bunny J. parva is only short-lived and just lives from a few months up to a year, but at least during its short life it doesn’t need to worry about predators. They are very toxic, because of the food they eat, which are sponges. All dorid nudibranchs (the group of slugs J. parva belongs to) are toxic because of their diet, and these toxins are often used in cancer treatments for people. Who would have thought that sea bunnies would be lifesavers, besides  being cute? But is the word sea bunny only referring to this particular species called J. parva? A quick search on the internet definitely tells us otherwise, it seems people refer to sea bunnies when they talk about any other dorid nudibranch with a fluffy and round appearance.

So, the question remains, do we have any sea bunnies in Norway? And the answer is yes, we do!

Sea bunnies of Norway (click to enlarge!)

And they are absolutely great and adorable to encounter underwater. Let us make a list of the sea bunnies of Norway, so we know what species we are talking about. Sea bunnies of Norway are; Doris pseudoargusGeitodoris planataJorunna tomentosaRostanga rubraCadlina laevis, Aldisa zetlandicaAdalaria loveniAdalaria proximaOnchidoris muricataOnchidoris bilamata,
Onchidoris pussilaOnchidoris depressaAcanthodoris pilosaDiaphorodoris luteocincta and I personally would draw the line at Goniodoris nodosa, as the other Goniodoridae don’t resemble that much the typical sea bunny characteristics. What do you think? Which species do you think are missing in this list, or which species should be left out?

I think it is time to take over the internet with our sea bunnies of Norway!

 

Furthermore
You want to see more beautiful pictures of sea slugs of Norway!

Check out the Sea slugs of Southern Norway Instagram account; and don’t forget to follow us.
Become a member of the sea slugs of southern Norway Facebook group, stay updated and join the discussion.

Explore the world, read the invertebrate blogs!

-Cessa

Door #16: Basic anatomy of the sea slug

Haminoea sp, photo by M. Malaquias

“Sea slugs” include both the by far most famous nudibranchs, and groups such as the Sacoglossa (sap-sucking slugs, more about these later in the calendar!) and Cephalaspidea (the bubble snails), amongst others. These latter ones often do have shells – but reduced ones, too small for the animals to completely retreat into, like this Haminoea:

Nudibranchs, however, are the “naked” snails: Their name “nudibranch” comes from the Latin nudus, naked, and the Greek βρανχια, brankhia, gills. They don’t have a shell, but this wasn’t always the case. In their early larval life stage, they actually have a shell, but when settling down and transforming from zooplankton into adults, they lose the shell. The loss of the shell in adults might be responsible for the amazing diversity we see in body forms present in sea slugs.

So, in this basic anatomy of sea slugs we will focus mostly on the body forms of nudibranchs, but all other sea slug orders are not far off from this anatomy, if you know the basics of nudibranchs, you can extrapolate to the other orders as well. So here we go!

Nudibranchs are roughly divided in two type of body forms; the dorid nudibranchs and the aeolid nudibranchs.

Two basic body types found within the Nudibranchia; the dorids and the aeolids. (Illustration: C. Rauch)

The dorid nudibranchs have a thick mantle that extends over their foot. In some species the surface of the mantle is covered with tubercles than can vary in different sizes, numbers and shapes. This gives them often a rigid body that offers some protection.  In most of the dorids it is the mantle that contains toxins to defend themselves, the toxins are extracted from their food sources.

Aeolid nudibranchs have mantles that are covered with finger-like extensions called cerata. The cerata are very special as they contain branches of the digestive tract, and in some species, this is also visible! The tips of the cerata contain special organs called the cnidosacs. Cnidosacs store stinging cells (called nematocysts). These are obtained from their food source which are often cnidarians like hydroids, sea-anemones and soft corals. The cnidosacs are activated when the nudibranchs feel threatened and the stinging cells will be discharged!

All sea slugs have rhinophores. On the head of all sea slugs you can find a pair of sensory tentacles called the rhinophores. They detect smell and taste and in most of the dorid nudibranchs the rhinophores can be retracted into a basal sheath. Sea slugs know all kind of shapes of rhinophores which are a very important tool for identification of the species.

Diversity of sea slug rhinophore shapes

Besides a pair of rhinophores many nudibranchs also have a pair of oral tentacles, one on each side of the mouth. They are most likely involved in identifying food by taste and touch.

Sea slugs also need to breathe oxygen. They do this via the surface of their entire bodies, but their main reparatory organ are their gills. Dorid nudibranchs have often a feather like structure encircling their anus on the back of their body (the branchial plume). Some dorid species can also retract their gills into a pocket. Within the aeolid nudibranchs the cerata act like gills by diffusing oxygen from the surrounding water. The cerata are sometimes branched in order to increase the surface area, also here, like the rhinophores, different species can have different forms of cerata.

Diversity of aeolid cerata shapes

-Cessa

Door #15: The eye of the beholder

It’s funny to see the different reactions to fresh material that comes in to the museum;  the exhibition team had  received some kelp that will be pressed and dried for the new exhibitions (opening fall 2019), and I ducked in to secure some of the fauna sitting on the kelp before it was scraped off and discarded. For the botanists, the animals were merely a distraction that needed to be removed so that they could deal with the kelp, whilst I was trying to avoid too much algae in the sample as it messes up the fixation of the animals.

I chose the right shirt for the day- it’s full of nudibranchs! (photo: L. Martell)

 

I then spirited my loot into the lab, and set up camp.

Count me in amongst the people who stare at lumps of seaweed.

 

Who’s there? The whole lump is ~12 cm.

How many animals do you see here? Which ones appeal to you?

I have made a quick annotation of some of the biota here:

Note that these are just some of the critters present…! (photo: K. Kongshavn)

Let’s go closer on a small piece of algae:

Now, what do you see? (photo: K. Kongshavn)

For Luis, the first thing to catch the eye was (of course) the Hydrozoa

Hydrozoans (the christmas light looking strings), encrusting bryozoans (the flat, encrusting growth on on the algae – you might also know them as moss animals), and some white, spiralling polychaete tubes  (photo: K. Kongshavn)

Did you spot the sea hare (Aplysia punctata?) Look a bit above the middle of the photo of the tiny aquarium with the black background. Do you see a red-pink blob?

Hello, Aplysia punctata! (photo: K. Kongshavn)

There were also several other sea slugs that I have handed over to Cessa for inclusion in the sea slugs of Southern Norway project, here are a few:

Then there were the shelled gastropods:

The brittle star from the earlier image – this is a Ophiopholis aculeata, the crevice sea star (photo: K. Kongshavn)

In fact, they both are Ophiopholis aculeata (in Norwegian we call them “chameleon brittle stars” – they live up to the name!), one of the very common species around here. (photo: K. Kongshavn)

One of the colonial ascidian tunicates (and some of the ever present bryozoa just below it) (photo: K. Kongshavn)

Most of these animals will be barcoded, and will help build our reference library for species that occur in Norway. I also hope that they may have helped open your eyes to some of the more inconspicuous creatures that live just beneath the surface?

2019 will see the start of a new species taxonomy project where we will explore the invertebrate fauna of shallow-water rocky shores, so there will be many more posts like this to come!

-Katrine

Door #14: Annelids from the deep Norwegian waters

We have recently started a new mapping project funded by the Norwegian Taxonomy Initiative (Artsdatabanken) on the deep-sea annelids. The annelid fauna in the deep areas of the Norwegian Sea, deeper than 2000 m, has recently been shown to be significantly different from the upper slope and shelf fauna. Morphology-based studies indicate that as much as 40% of the deep-sea annelid species are new to science, and initial results from DNA-barcoding provided even higher numbers. This project aims to characterize, describe and map these unknown species of annelids and will provide much needed baseline knowledge for monitoring of environmental effects from future deep-sea mining and other human activities.

Figures: Tom selecting 96 specimens of annelids from HAUSGARTEN for DNA barcoding.

We have started the project by processing a number of samples from a German expedition on RV Polarstern to the long-term research observatory HAUSGARTEN located at the Fram Strait. The samples have been collected between 1000 and 5000 m depth and harbor more than 30 putative morphospecies. We are going to barcode 96 individuals from this material to supplement the barcode library of the Norwegian annelids and to help resolve taxonomical problems within several taxa.

-Nataliya

 

Door # 11: Animal rocks and flower animals

The phylum Cnidaria is a diverse group of animals united by their ability to synthesize a complex type of ‘stinging’ cells called cnidocytes, which they use to hunt for their prey. The more than 13 000 species of cnidarians come in many shapes and colors, from the familiar jellyfish and corals, to the less famous myxozoans, hydroids, and siphonophores (read some more about those here). Because cnidarians live and thrive in marine and freshwater environments all around the world, humans have become familiar with them since ancient times: they have been feared for their sting, worn as jewelry, or simply admired for their beauty.

Sea nettles (genus Chrysaora) and ‘terrestrial’ nettles (genus Urtica) belong to very different groups of organisms, but share their name because of their stinging abilities. In some languages, like Norwegian and Swedish, cnidarians are called “nettle animals” (nesledyr and nässeldjur, respectively). Photo: Luis Martell (left), Nannie Persson (right).

Despite this familiarity, the true nature of cnidarians long remained unclear to naturalists and non-professionals alike. Perhaps to a greater extent than any other large phylum in the animal kingdom, people have historically failed to recognize cnidarians as animals, or even as living beings. Early civilizations had some knowledge about corals, sea-anemones and large jellyfish, all of which were encountered frequently along the coasts, but although fishermen and sailors knew about the existence of coral reefs (the massive bodies of coral represented major hazards for navigation), the animals themselves were probably seen only as pieces of rock. Some of the sessile species of cnidarians with a hard skeleton were considered minerals until the second half of the 17th century, when the use of magnifying lenses and the invention of the microscope allowed scientists to realize that the stony coral fragments washed up on the shore were actually made up of small flower-like organisms.

With their tentacles surrounding a central disc, sea anemones (in the image a specimen of Aiptasia) look somewhat like submarine flowers. Their plant namesakes (for example the wood anemone Anemone nemorosa) are strictly terrestrial. Photo: Joan J. Soto-Àngel (left), Nannie Persson (right).

Historically, the most persistent confusion regarding the cnidarians has been with plants and algae. For more than 1 500 years, the immobile sea anemones, sea fans, and hydroids were thought to be strange marine flowers and were consequently studied by botanists, not zoologists. They grow attached to the substrate and many species die if detached, which left early naturalists in doubt as to whether they were plants or animals. Thus, the category ‘zoophytes’ (from Ancient Greek ζῷον, zoon, ‘animal’ and φυτόν, phytón, ‘plant’) was created for them. It was only in the first half of the eighteenth century when this view started to change, thanks to the observations of J. A. Peyssonnel and the work of botanist Bernard de Jussieu, who together managed to convince their colleagues about the animal nature of the zoophytes.

The ‘sea tomato’ (Actinia equina) is a common cnidarian along the Atlantic coasts of Europe. It may look like a tomato when it is not covered by water, but is not related to its vegetal look-alike. Photo: Nannie Persson

The flowers of submerged marine plants (like this Cymodocea nodosa) are usually not as colorful or conspicuous as sea anemones and corals. Photo: Joan J. Soto Àngel

Today we know more about these organisms and there are no longer doubts about their affiliation to the animal kingdom, although we can still see evidence of their botanical past in the names of several cnidarian groups. The word Cnidaria comes from the Greek word κνίδη (knídē, meaning ‘nettle’, referring to the plant genus Urtica), and was inspired by the stinging power of the plants. One of the largest groups of cnidarians, the Anthozoa (which includes the flower-looking sea anemones and corals) is aptly named with a word deriving from the ancient Greek roots for flower (antho-) and animal (-zoa). Because there are still many open questions in cnidarian biology, initiatives that chart the diversity of cnidarians (like the successful project HYPNO and the upcoming project NORHYDRO) are necessary to get to know more about the particularities of these interesting animals!

-Luis Martell and Nannie Persson 


References:

Jussieu, B. de, 1742. Examen de quelques productions marines qui ont été mises au nombre des plantes, et qui sont l’ouvrage d’une sorte d’insecte de mer. Mem. Acad. Roy. Sci. Paris, 1742, 392.

Edwards, C. 1972. The history and state of the study of medusa and hydroids. Proc. R. S. E. (B). 73, 25: 247-257.