Is the vampire squid an octopus or a squid?

Here’s another simple but difficult question that came up this week on Twitter prompted by cephapodologist @Thomas_Clements reaction to a tweet put out by the team behind the E/V Nautilus deep sea rover twitter account which used a popular science fact about vampire squid which read as such:

Did you see it?! We had an extended visit with a Vampyroteuthis infernalis (literally meaning “vampire squid from hell”). Neither a squid nor octopus, this fierce-sounding cephalopod actually fishes for marine snow using two retractable filaments and mucus-covered suckers!

Now, as you may have gathered from the title of this post, the bit I’m interested in is the ‘fact’ about vampire squid being neither an octopus or a squid. It’s a common enough fact you can find out and about in the edutainment and sci-comm resources and there’s something about the trope of telling people that a name we’ve just told them doesn’t mean what it is commonly assumed to which science communicators love. Whether or not ‘not facts’ help with engagement or learning I remain to be convinced.

Thomas, who surely knows his nidamental glands from his accessory nidamental glands, quoted the tweet stating that vampire squid are in fact octopuses. At this point I got involved too possibly disagreeing with him, although even with 280 characters discussions went around in circles. So. Once and for all. Are vampire squid octopuses, squid or neither and can we change the flipping name in any case? Because like starfish vs sea stars it’s a waste of valuable attention time telling people what something isn’t rather than what it is.

Tl;dr

The predictably and utterly unsatisfactory answer to the question, like many questions in science is. It depends. We probably can’t change the name either. It’s a good one. We’re stuck with it. You can finish reading here if you want to save yourself some time.

L;r

For those of you in for the long haul, here’s why ‘it depends’ and it’s all tied up with when scientific language bleeds and overlaps into common usage and something I’ve written about before with the idea of ‘true’ and false animals. It’s also at the heart of one of my favourite reads on a closer-to-home-taxonomically-speaking topic by Paolo Viscardi, dealing with the same thing when it comes to whether apes are monkeys or not.

Squampire Vids

So first, what kind of animal is a vampire squid when it’s not being torn between deciding to be an octopus or squid? Vampire squid are cephalopods, the group of molluscs that also includes nautiluses, octopuses, cuttlefish, ammonites, belemnites, bobtail squid and others. Today they are thought to be represented by a small single living species, the excellently named Vampyroteuthis infernalis, however, a number of extinct forms have been described which is surprising given that the soft bodied cephalopod fossil record is generally quite poor. Vampire squid superficially look similar to some octopuses in that they lack tentacles, have a web between their arms and also rock the largest eye in the animal kingdom relatively to body size*. Indeed, they were initially thought to be an octopus when first described by Carl Chun. Through the wonders of linked connected data and libraries, if your German and interpreting Gothic script is up to it, you can check it out yourself over at the Biodiversity Heritage Library right here where vampire squid were first described in 1903 on page 88 and again here on the bottom of page 132 when Vampyroteuthis is put in its own family. Previously, it was believed to be related to similar looking cirrate octopuses because of the cirri (cilia like projections) on the arms but was thought a distinct kind of octopus due to possessing a radula which cirrate octopuses lack and the nature of the fins. Interestingly, in the original description is was described as a ‘tintenfisch’ (ink fish) which, like other European languages, is a catch all term that could mean squid, octopus or even cuttlefish but taxonomically it is placed firmly with other octopuses in the text.

Later it was placed in it’s own group, the vampyromorpha or vampyromorphida due to unique features such as photophores and two velar filaments, retractile sensory filaments used in a form of filter feeding which can be retracted into special pouches. At one point these filaments were thought to be specialised tentacles (a squid character) but are possibly a different arm pair, the same one presumed to have been lost by octopuses. Is this confusing enough for you?

The first illustration and use of the name Vampyroteuthis infernalis. Chun, Carl. 1903. Aus den tiefen des weltmeeres. Image from Biodiversity Heritage Library. Link to volume in references.

Hierarchy Rules

So in this Linnean (after Carl Linnaeus) sense, that is the old school taxonomic sense where we divide up organisms and put them into discreet hierarchical boxes defined by shared characteristics, vampire squid are different enough to all octopuses to belong to their own order (the taxonomic level below class and above family), the Vampyromorpha. They are not octopuses, which have their own order, Octopoda. Together the eight armed cephalopods, the octopuses and vampire squid make up the superorder Octopodiformes. Nor are they squid which make up several orders that were thought to be in a separate branch of the soft bodied cephalopod tree superorder Decapodiformes, the ten limbed soft bodied cephalopods. Not octopuses. Not squid.

An extremely conservative classic ‘Linnean’ classification of the living coleoidean cephalopods (sorry nautilus). Think of it as a family tree reading left to right with parent terms on the left with their children to the right. Note no suggestion of relationship is inferred between these groups.

Evlolutionary Blylology

However, although still a basis for taxonomy this Linnean way of ordering the world doesn’t fit with how we know evolution works. Although we might be happy to group living animals in separate groups such as birds, mammals and reptiles we know from fossils, genetics and molecular studies that the ancestor of birds was a reptile as was the ancestor of mammals and all reptiles evolved from amphibians. When we factor in evolutionary relations animals, plants and other organisms aren’t discrete groups that sprung into being forever distinct or designed. When we trace relationships back far enough we converge on ancestors of many different kinds of animals.

When Carl Chun described the vampire squid, he was looking at just the superficial characters and assigning it to a group based on those shared characters. Unfortunately, interpreting these characters can be subjective. Some of these characters may not actually be important in working out true relationships. Others may have evolved independently in many groups so not a useful character for working out relatedness. For example, powered flight has evolved multiple times in insects as well as birds, bats, pterosaurs and controversially cephalopods so adaptations and anatomy for flight have a shared function but not a shared origin.

Beyond Chunners

Today we have more fossil evidence and molecular analyses of living species which shed light on the evolutionary history of organisms. From fossils we can see where characters have been lost or gained over time and through genetics we can trace evolution through the changes in genetic code. Interpreting genetic and fossil evidence is still a subjective exercise, it’s a widespread assumption that we can just examine and compare genetics to come up with true evolutionary relationships, however, interpreting the complexity of genetic sequences and depending on different computational techniques to compare them results in even more confusion over ‘true relationships’. This now dated paper from 2007 nicely demonstrates the complexity of constructing the relationships of different cephalopods from mitochondrial DNA giving nine similar but different relationships across the groups depending on tools used to infer relatedness sometimes not consistent with the old Linnean orders (Strugnell and Nishiguchi 2007). Another drawback of molecular analyses is that it’s impossible to include data from older fossils.

For argument’s sake and so we can actually get back to the question at hand, let’s pretend that there’s a degree of consensus on the broader relationships of the cephalopod group and assume this diagram by Clements (the very same) et al. 2017 showing the relationships between the soft bodied cephalopods (sorry nautiluses, ammonites etc.), gets it mostly right.

Phylogeny of the major coleoid groups. From Clements et al. 2017. Figure 2.

You can see that instead of having discreet branches that we might call superorders, orders etc. this diagram shows the theoretical relationships between living groups punctuated with problematic fossil groups and nicely the diagram highlights where evidence of these exists. Vampire squid, Vampyromorpha here, and octopuses (Cirrata and Incirrata) are three branches at the top. So are vampire squid octopuses? Well here’s where it depends. There are some guidelines and codes which must sometimes are followed for the creation of scientific names (it is still a bit of a Wild West when it comes to higher level clades and taxonomies**). When it comes to common names for animals and especially groups of animals, however, there aren’t any rules because who are scientists to say what we should and shouldn’t refer to animals as outside of the technical literature? This is where common usage of terms smashes into scientific usage and in many cases common usage doesn’t make sense biologically, but then why should it? You shouldn’t need to be a taxonomic authority to order your meal in a restaurant so seafood/shellfish works fine as an ugly messy category. You shouldn’t need to consult an identification key to point out ‘worms’, ‘frogs’ or ‘butterflies’ in the garden either. In day to day life these terms work and rarely cause great offence.

Are You Still Here?

So where does the issue with vampire squid come in? It really depends on how much you care and know about the relationships within the group and in reality who you are trying to communicate with I guess and we can edit the diagram above to highlight what we could mean by octopuses:

Two ways in which ‘octopuses’ could be defined. Yellow group A includes all vampyropods. Red group B is just incirrate and cirrate octopuses. Modified from Clements et al. 2017. Figure 2.

Going back to the tweet that started this whole thing, vampire squid are octopuses in the sense that we can group the whole of the Vampyropoda branch into group A as being ‘octopuses’ so this would include vampire squid, both cirrate and incirrate octopuses and the two fossil groups. Traditionally vampire squid have been separated from octopuses so here group B would be the octopuses and vampire squid would be off on their own. You could construct another group that just included cirrate + incirrate octopuses and Teudopseina as ‘octopuses’ and vampire squid separately. Here vampire squid are inferred to have split from octopuses at the same time as Prototeuthidina so if we’re being consistent either both or neither should be ‘octopuses’. Are they octopuses then? I guess that entirely depends on where you draw the line and I imagine most people just don’t care enough to. You decide!

Nearly Done

How about squid then? If the common usage of squid wasn’t problematic enough, scientifically it makes even less sense and is very similiar to the apes are monkeys link above. ‘Squid’ don’t form a nice convenient group and the term is used inconsistently through the quirks of historical description. For example in this diagram at the bottom Spirulida are ram’s horn squid, Sepiolida are bobtail squid, and teuthids comprises various different groups of ‘true’ squid. Confusingly, Sepiida includes one group which are informally called bottletail squid (sometimes placed in the Sepiolida) and another group that is the cuttlefish. It’s not even consistent within the group let alone across the group. So if we plot ‘squid’ on the diagram, below, you can see it really doesn’t make sense at all. If we’re being consistent this would also mean that octopuses and Teudopseina were also squid. So vampire squid aren’t squid if we’re ignoring cuttlefish and assuming some kind of coherency amongst the different kind of squid at the bottom. We’d need to decide if belemnoids and the other extinct cephalopods were also ‘squid’ or not. So it’s in this highly obscure and opaque instance that we’re referring to when we say that vampire squid aren’t squid but of course they’re still called vampire squid. Not squid.

Getting very silly now, if vampire squid are squid then all coleoids should be! Modified from Clements et al. 2017. Figure 2.

To round up then, is it actually of any use to most people to spread facts like ‘vampire squid are neither octopus or squid’? I’d say it isn’t in most instances as the basis for the statement is rooted in a mire of taxonomic pedantry and I imagine most people won’t be able (willing more likely who has the time) to really scrutinise what that means and as I’ve hopefully shown albeit in a round the houses way, it really does depend. Using the same diagram we could also come up with facts such as octopuses aren’t octopuses they are vampyropods or ram’s horn squid/cuttlefish/bobtail squid aren’t squid. The ‘fact’ is perhaps a compelling one as it’s ridiculous and obviously confusing so perhaps it’ll continue to be perpetuated without anyone really understanding what it means because that’s the beauty of being human and it’s all a little too Orwellian going around telling people what they can and can’t, should and shouldn’t say.

*Another one of those facts. A blog post for another time perhaps.

** It can be impossible to keep on top of even the higher level taxonomic, phylogenetic and cladistic terms even for a tiny relatively simple group like cephalopods and there’s some disparity in use across zoology and palaeontology here’s a run down of confusing terms some of which are sort of synonymous. Sometimes. Octopodiformes, Octobrachia, Decapodiformes, Decabrachia, Vampyromoprha, Vampyromorphida, Vampyropoda. Most people kind of acknowledge that Teuthida probably isn’t a coherent group but whaddya gonna do? Sepiolida sometimes exists, sometimes doesn’t. Decabranchia (note not Decabrachia) is sometimes still used to refer to Oegopsina (sometimes in Teuthida, sometimes not) and rarely now Decapoda sometimes means the same thing, not to be confused with Decapodiformes or indeed Decapoda in the crustacean sense. Another convention in the scientific literature is to differentiate between octopuses and octopods. Octopuses being in the family Octopodidae and all other non-Octopodidae ‘octopuses’ octopods. MADNESS I TELL YA MADNESS.

References

Chun, Carl. 1903. Aus den tiefen des weltmeeres. Biodiversity Heritage library Link to volume.

Chun, Carl. 1915. Die Cephalopoden T. 2: Myopsida, Octopoda. Wissenschaftliche Ergebnisse der deutschen Tiefseeexpedition auf dem Dampfer Valdivia 1898–1899, 18(2), Biodiversity Heritage library link to volume.

Clements, Thomas & Colleary, Caitlin & De Baets, Kenneth & Vinther, Jakob. 2017. Buoyancy mechanisms limit preservation of coleoid cephalopod soft tissues in Mesozoic Lagerstätten. Palaeontology. 60. 1-14. 10.1111/pala.12267.

Strugnell, Jan and Nishiguchi, Michele, K. 2007. Molecular phylogeny of coleoid cephalopods (Mollusca: Cephalopoda) inferred from three mitochondrial and six nuclear loci: a comparison of alignment, implied alignment and analysis methods, Journal of Molluscan Studies, Volume 73, Issue 4, Pages 399–410, https://doi.org/10.1093/mollus/eym038