—People used to think a biologist was someone catching butterflies with a net, searching for tigers, or at worst, experimenting on lab mice. Nowadays, a biologist is a person in a lab coat, either holding a test tube or peering into a microscope. Is this really the case, or is "classical" biology still alive?
— Of course it's alive. It has just been enriched with molecular methods. For instance, in my work, we determine the gene sequences of different worms, construct a phylogenetic tree[1], and then examine it. In other words, classical zoological taxonomy is now based on both anatomical and molecular features. Moreover, it is now considered good practice to have both quality morphology and molecular studies.
Of course, it's not always possible because all samples are different. For example, most of the samples my colleagues bring me are either preserved in formalin or 70% alcohol, making it difficult to work with them further. But yes, the way we describe species has changed.

— What has radically changed in our understanding of taxonomy with the introduction of molecular methods for reconstructing phylogenetic trees?
— Quite a lot. Take this simple example. It turns out that there are many cryptic species[1] that we previously couldn't distinguish either morphologically or anatomically. However, after molecular analysis, it becomes clear that there are two different species, and you start trying to pinpoint their differences. There must be something, right? Morphology, anatomy, development process... It’s possible not to find any difference, or find something totally unexpected. For instance, two supposedly identical species might turn out to have completely different larvae. Cryptic species are species that are difficult or impossible to distinguish from each other based on morphological traits.

— Completely different or just slightly different?
— It depends on how you look at it. They could be slightly different, or they could be very different. This is particularly important for the species and groups that have few morphological features. I work with phoronids (Fig. 1), which externally all look the same. Even I can't identify them by sight. You first need to dissect them and make 3D reconstructions of certain organs. In such cases, molecular analysis is extremely helpful.

— Do indistinguishable doppelgangers also form different communities?
— I can't say for sure, but I believe they do.

— So, until molecular science came along, no one thought to notice that there were clusters of seemingly identical phoronids that formed associations with completely different organisms. And to consider that maybe this wasn't a coincidence and they were indeed different, and start examining their morphology.
— That's exactly right. Moreover, when it comes to hydrobiological studies, i.e., just collecting all the macrobenthos of a specific water area, phoronids are not even identified. They are just classified as phoronids, only up to the rank of phylum. And some can't even do that. They write "annelids" when it's actually phoronids.

— That's the so-called microtaxonomy. We thought it was one species, but it turned out to be fifteen. And what about global changes? Linnaeus had it simple with mammals, birds, reptiles, fish, insects, and worms, with the latter encompassing all we have discussed.
— In fact, molecular science has made an incredible breakthrough in large-scale phylogeny, at least in the phylogeny of bilateria[1] and multicellular organisms in general. What do I mean here? Kenneth Halanich[2] and his colleagues showed in 1995 that phoronids are relatives of protostome animals, not deuterostomes, as was always thought... Protostomes include, for example, segmented worms and mollusks, and deuterostomes include you and me, echinoderms, and the poor hemichordates, of which there are few.

— And the insects?
— Insects belong to Ecdysozoa[1]. That's my next point. In 1997, Dr. Anna Marie Aguinaldo and colleagues in Nature stated that nematodes were relatives of arthropods. The Ecdysozoa group was identified, and now the entire system of bilateria doesn't resemble what it was before 1995, because before it was parenchymatous, coelomates, pseudocoelomates, and so on. (Fig. 3). And suddenly it turns out that nematodes and crayfish are close relatives.

— A lot of blood was spilled before that was established.
— Indeed, it was a hard pill to swallow. Arthropods were separated from annelids[1], and this group, Articulata, which Cuvier had identified in some bygone era and which suggested that arthropods had evolved directly from annelids. So, molecular biology shook up the entire phylogenetic tree, but it has now stabilized. We have Spiralia, Ecdysozoa, and Deuterostomes. And now, we exist within this paradigm.

— How stable is this paradigm? Could it be that in another 25 years, we'll discover that everything was incorrect?
— I don't think so, because there is both morphological and molecular evidence to support it.

— Where does the morphological evidence come from? The previous taxonomy was based on morphology. Then molecular scientists came and redrew all the trees, and the morphologists said, "Well, that works too. We'll now identify the correct morphological characteristics using your new trees."
— I understand what you're implying. These ecdysozoan conflicts had been going on for a long time. Our faculty of biology only started teaching the new system about ten years ago because it was too difficult to grasp. But in reality, there are indeed common morphological traits that were overlooked... or perhaps they weren’t given enough weight.

— Does the concept of "phylum" even make sense? Species, at a basic level, of course, mate with each other and don't mate with others. But do all the other taxonomic ranks make sense, or is it just an attempt to impose a discrete hierarchy onto a continuous tree?
— Indeed, it's an attempt. This is all a product of human imagination. But we need to categorize our surroundings somehow.

— You still use these concepts in your work. But what are phyla, exactly? Did the phylum Chordata and the phylum, say, Polychaeta form at the same time if we compare the timing of the first branching within phyla? Or are chordates younger than polychaetes? And if so, why do we refer to both as phyla?
— They all emerged during the Cambrian period. Before the Cambrian period, multicellular organisms included the Vendian fauna, such as Dickinsonia and others. But we don't know whose descendants survived. For instance, lophophorates supposedly dating back to the Precambrian era were described not too long ago. I'm interested in this because phoronids are lophophorates. And now, some very peculiar reconstructions are being made. I'm not a paleontologist, so it's difficult for me to determine what can be gleaned from these findings... But the reconstructions look odd, and in this form, no lophophorates could have survived to our time. But if we follow the authors' logic, this was an ancestor, followed by radiation in the Cambrian period.

— If I understand correctly, all current phylum-level taxa emerged in the Cambrian period as separate branches of the tree, right?
— Not necessarily as separate branches. They might have emerged at the level of some ancestral forms. The first branching into the ancestors of modern phyla happened during the Cambrian explosion.

— So, the concept of a phylum-level taxon makes sense because it represents rapid radiation, just like mammalian orders make sense because they started branching dramatically 70 million years ago.
— I've never really considered it in terms of some timeline. I always thought that phyla were animals with a unique structural plan.

— Do you believe in paraphyletic taxa?
— Is this a question of belief? [Laughs.]

— Fine. Would you consider using paraphyletic taxa in your scientific work?
— I believe I would.

— Is it because they share a common morphology? Then what about the fact that they have a long foreign branch sticking out from within? Take the classic example of whales, recently found to be even-toed ungulates. They don't have any hooves, of course, but molecularly they are even-toed ungulates. There's no way around it. So, by the party's and government's latest decisions, the order of cetaceans has been abolished.
— I wasn't aware of that!

— That's it. There are no more cetaceans or even-toed ungulates. Disregarding morphology, people have forcefully established the monophyletic order of Cetartiodactyla just to avoid having a paraphyletic order. And this is indeed a
— I agree, yes. Although as a morphologist, it's hard for me to see whales as even-toed ungulates.

— And what about birds being reptiles?
— That's easier because it's something I learned in school.

— Snakes, by the way, have also been canceled. They are now lizards.
— Lizards, huh? Well, at least they're not even-toed ungulates.

— They seem to be closer to iguanas, chameleons, and monitor lizards, and only then skinks and geckos. Overall, snakes are deeply embedded within the lizard tree.
— I didn't know that about snakes... It's a big problem in general. We often sit in our offices unaware of what's happening in the next room. That's why we organized a research seminar in our department. It turned out to be incredibly useful, especially for us. There was an attempt to hold interdepartmental seminars at the Academic Council, and we had them regularly for a while. But then it all fizzled out because people didn't have time to prepare presentations. It's a pity because you could be listening to a microbiologist and thinking, "My God, I've seen bacteria... We should collaborate and do research on the bacteriome of some..."

— Of course, there are lots of bacteria on worms.
— On them. In them. In the tubes. Everywhere.

— How many people attend your zoology seminars?
— It really depends on the topic. Leonid Rusin gave a presentation on how new technologies, like single-cell analysis, help us understand the origin of multicellular organisms. It was a great, well-structured, and easy-to-understand presentation. Because for a hardcore zoologist, all these single cells are a complete mystery. The topic was interesting and attracted many people.

— Which seminars attract few people?
—More narrow ones. We once held a seminar on the evolution of brachiopods. A fascinating subject and a collaborative effort between Tatiana Kuzmina and myself. It felt as if we had invented a time machine because we reconstructed the life cycles of extinct brachiopods. There used to be many more of them in the past, and how they lived, what they did, and how they reproduced remains a mystery. However, this might be of interest to paleontologists and modern lophophorate experts, but it probably doesn't appeal to the majority of people, which is why the seminar had a low turnout.

— Do the students attend the seminars?
— Not many of them, mostly PhD students. But there are some committed students, including those who participate in academic contests. At first, they feel the need to learn everything, but this enthusiasm tends to fade rather quickly.

— Returning to our initial discussion about popular and unpopular biology, which departments do biology contestants choose?
— It varies greatly. Last year, I led a group in Zvenigorod consisted of Biology Olympiad students. Among them was a particularly remarkable young man who declared, "I'll pursue molecular biology, of course. It's the reigning queen of all biology" and so on. I explained to him that while molecular biology is indeed important, its methods are universally applicable, including in our field, and understanding diversity is beneficial. Ultimately, he chose our department.

— Often, the most fun part is when someone has a solid grasp of classical biology and identifies fascinating subjects that others have yet to explore. However, merely understanding zoological exotics isn't enough. One also needs to see the interesting possibilities they present. And if you're unaware of something like transcriptome analysis, you simply wouldn't think to utilize it.
— Of course, it's essential to have a grasp of the range of methods available. But to become an expert...

M.G.: Being able to count is optional, yes. There will always be someone who can do the calculations. It's not an issue.
E.T.: That's what we're reckoning upon.

— Typically, there are more individuals willing to do the calculations than those who understand exactly what needs to be counted.
— [Laughs] I couldn't agree more. Our international colleagues seem to have a certain issue, although I'm not in a position to pass judgment...

— They don't have proper zoology.
— Yes, and this leads to certain issues because they have advanced methodology and have the equipment, where they insert anything they can get their hands on... For instance, they've looked at gene expression in phoronids. The reasoning behind this is utterly unclear, as is the outcome. The description isn't just incorrect, it's completely turned upside down. In short, it's quite upsetting. Sometimes, I don’t know just how to cite such studies. Yes, they've discovered that a certain gene is expressed in a specific location. So what? What are the implications? I would have conducted a thorough study on gene expression in phoronids and brachiopods.

— If you had access to grant funding and had a competent graduate student who could set up a transcriptome experiment and do the calculations, what would you do with phoronids and brachiopods?
— First, I would investigate the origins of their structural plan. Expression should be conducted on both the dorsal and ventral sides[1]. There must be genes that mark them. There is actually a belief that these groups are related. In fact, some molecular phylogeneticists categorize phoronids as a subset of brachiopods rather than a separate phylum...

— Just now, you were telling me that God created the phyla in the Cambrian period, and they've all been happily crawling around ever since. But now it turns out that phoronids are nested within brachiopods.
— Yes, according to Mr. Cochin's theory, a researcher from the UK. I'm not sure where he got this idea from. But he's a molecular scientist, and his views on this topic are quite unconventional, albeit trendy.
In 2015, I published a paper in PLoS One where I attempted to demonstrate the monophyly of lophophorates morphologically, arguing that phoronids, brachiopods, and bryozoans form a monophyletic group. He responded with a letter saying, "Why are you morphologists meddling in phylogeny? That's our job." He was polite but insistent that morphology is incapable of resolving these issues and that we should leave it to molecular phylogeneticists. He has a paper in which he claims that phoronids are essentially shell-less brachiopods. However, the structure of these two groups are entirely different.

— Hold on. Nematodes and insects also have different anatomy structures. Yet you eventually accepted the molecular trees, as you had no other choice.
— Yes, but these are two distinct groups. Nematodes are a phylum. As far as I know, that hasn't been disputed yet. And insects can be classified as arthropods. Phoronids, however, should not be classified under brachiopods. They fold on the dorsal side, while brachiopods fold on the ventral side. I believe this is a significant difference. We see evidence of this folding in the larval development of brachiopods, but opinions vary. Some see it, while others don't. Some argue that it's not folding at all, but rather a slight twisting of the larvae. However, gene expression could help us identify the genes that mark the dorsal and ventral sides during larval stages, i.e., during metamorphosis, which is crucial. In adults, it's more or less evident.

— Do you think the expression of these marker genes is preserved across phyla?
— I believe so. Why not?

— I don't know. Insects and vertebrates both have a dorsal-ventral axis. Both crawl on their bellies. Are the same genes responsible for this differentiation?
— I'm not sure. I haven't delved that deep into it. This idea came about when Rusin attended the seminar on brachiopods and asked, "Why are you morphologists fussing over larvae?"

— First, you need to examine a well-known subject to understand whether the basic gene expression regulators are preserved. Otherwise, you might find that development is different, and you won't see anything. In essence, if you have the complete genomes of the organisms you're capable of cultivating, then all of this can be accomplished.
— I was interested in studying regeneration, which is a popular topic these days. Phoronids regenerate quite easily. They can simply regrow their heads, which are regularly bitten off by fish, crustaceans, and mollusks. They can also literally lose their heads after fertilization and quickly regenerate them. We want to first examine proliferation at the anatomical and then cellular level, followed by a proteomic analysis with colleagues from Spain.

— Has the trendy evo-devo reached you yet?
— It has reached us, but not me specifically. Some people in our department are utilizing these methods, but the results vary. You need to have a lab where this can all be done properly. Right now, we're attempting to do so. However, it's going to be challenging in the current situation.

— Imagine we're having this conversation six months ago, and you're leading a major project with ample funding. What would you do that interests you? Not for the sake of humanity but for your own sake.
— Goodness! [Laughs] Not for humanity but for myself, you say? I'm not sure. I feel somewhat taken aback. I would purchase all kinds of amazing equipment.

— And what tasks would you want to work on?
— What tasks... Something studying morphology, probably... Followed by taxonomy based on morphology and perhaps molecules.

— Great. You've sequenced genomes, drawn phylogenetic trees, and mapped morphological changes onto them to understand the meaning behind their branches. But what about the molecular trees where phoronids are nested within brachiopods? You say these molecular trees aren't credible because the morphology is entirely different. So, do you deem molecular trees credible or not based on morphological considerations?
— How should I put it? For instance, Chaetognatha, or arrow worms, is a very strange phylum that has traveled all over the bilaterian tree. Initially, morphologists grouped it with the deuterostomes due to their similar anatomy, three coeloms, and radial cleavage. As for molecular biologists, they've done all sorts of things with it! Arrow worms had been classified as Ecdysozoa and also as Lophotrochozoa. Now, several papers have been published in Nature, placing them in Gnathifera (Fig. 5), a group that has jaws. It includes some very peculiar creatures such as rotifers, thorny-headed worms, Micrognathozoa, and gnathostomulids. They possess a unique jaw apparatus, the mastax, which are jaws inside the pharynx (Fig. 6) that can be ejected. These jaws are compared by molecular phylogeneticists to the bristles of arrow worms, which have a capturing apparatus consisting of pairs of bristles on the heads.
But here's the thing. Firstly, these are all ectodermal structures, whether in the mouth or on the head, but it's somewhat strange. How do they picture a jaw emerging onto the head? More fundamentally, the structure of these jaws is entirely different (that's why we need all this morphology, including the electronic one) because in arrow worms the bristle is like a tooth. It has a pulp inside consisting of cells that are extensions of epidermal cells, while in normal gnathifera it's just a cuticle into which no cells or even cell outgrowths pass. At most there may be microvilli. I don't think the people who attributed arrow worms to gnathifera are entirely wrong, but this is a case where it needs to be tested specifically with morphological methods.
Or the poor bryozoans... They too have been up and down the tree. They have never been classified as Ecdysozoa, but they have also been among Lophotrochozoa as well as at the base of the tree. In the end, they are probably lophophorates.

— When someone is moving all over the tree like that, it means the branch they're sitting on is very short and therefore unstable.
— Yes.

— That means that there really is no binary tree but just large nodes from which several branches grow at once, which makes this whole situation hard to resolve. And if there is an unresolved node from which all three grow, won't there always be common morphological features that separate any two groups from the third simply because they all grow from the same node?
— It's complicated. Speaking of bryozoans, they have traditionally been grouped with animals that are simply small in size. Bryozoans form colonies, but the individual zooids are small. Secondly, they have some sort of ciliary apparatus, so they have also been grouped with bellflowers and Symbion.

— Like it's a big deal! Even vorticellas have a ciliary apparatus.
— It's different in vorticellas as they are unicellular organisms. It is believed that Symbion initially had tentacles, which then shrank. And since Symbion animals are very small, only cilia remain from the tentacles.

— So there is just a single cell left from each tentacle
— Sort of. Or a cluster of cells. And all these little animals are placed into a single group, which Andreas Hejnol and his colleagues named Polyzoa in 2009. Bryozoans have stayed there for quite a while, but they actually have a lophophore. It's a very specific organ, and it's very similarly organized in different animals. We are currently writing an article for a special issue of the Journal of Morphology, which will be titled Homology. And we are trying to express this idea of lophophore homology. And bellflowers have tentacles, but they are not lophophores because both their mouth and anus are located inside the corolla, which contradicts the basic definition of a lophophore.

— But if you take another pair now, you will also find they have something in common that the third one doesn't have.
— Yes, I will.

— That's exactly what I meant. When we have three poorly resolved taxa, you can always morphologically combine two against the third one.
— That's why it's necessary to not only build trees, especially when they are built by people who have never seen animals.

— Why do you need to look at animals to build molecular trees?
— I think it's important to understand what the animal looks like.

— I think so too. But on the other hand, the computer is made of metal. You load sequences into it, and it draws a tree for you. Who cares what anything looks like? Perhaps the pressures of the morphological tradition will actually be harmful at some stage.
— That's true. I'm certainly feeling that pressure, to be honest. [Laughs]

— Okay, let's take a few steps back. You've bought microscopes, prepared slices, looked at cells, and described the structure of everything in the world. What next?
— Then I'll look at the development process of everything in the world. I'll use the same microscopes but different techniques: gene expression, blastomere tagging... I'll need some very precise instruments for that.

— What will you use for tagging?
— A type of fluorescent dye, which will allow me to trace the descendants of that particular blastomere.

— So, you take a blastomere, inject it with something luminescent, and then observe how its offspring are dispersed within the embryo, right?
— Yes.

— I've been trying to steer you toward single-cell sequencing, but you seem to resist.
— [Laughs] I'm not easily swayed into it. I'm currently apprehensive about this topic as it's completely new to me. But overall, it's a fascinating topic. It's almost like a glimpse into the future.