You can rifle the Pertwee era for tentacles and find relatively few. They only crop up in stories in which capital looms. They only fully-materialize as a major threat where capitalism is a systemic presence, threatening - even if only obliquely - to connect up various social and political nightmares.
That isn't to say that social and political nightmares are thin on the ground. Far from it. But it's only when those problems are connected to capital, commodification and trade as exploitative or destructive, that they sprout tentacles.
Evidence of Absence
The reason why 'Spearhead from Space' builds to an unexpectedly tentacular conclusion is because all sorts of things within it hint obliquely and elliptically at deep problems in the Britain of the late twentieth century, problems which seem to build towards a connection that must be occluded: namely the connection of all these problems at the economic base of society, the productive forces, the capitalist factory, the commodity form itself. 'Spearhead' is saturated in depictions of hierarchy, domination and class. The story hints - albeit very quietly - at imperialism, and at racial and gender hierarchies. The monsters are stalking emblems of alienation and commodity fetishism, manufactured things, products, hostile commodities in the estranged human form of consumerism. The tentacles appear to obscure the hub of the story. We don't even see the hub of the creature within the tank, only its flailing limbs.
'Spearhead' is, however, unusually potent, oneiric, suggestive and loaded. That said, many of its preoccupations recur throughout the Pertween era... just not together, not in such a 'joined-up' way and not in stories that even notice capitalism, let alone suggest that evil emanates from capitalist alienation of labour.
For instance, in 'The Silurians', social hierarchy is definitely in evidence but it doesn't reach deeply into everyday normal life as in 'Spearhead'. Work is in evidence, but almost all of it takes place in a state-owned research centre and all the main characters are professionals who are, apparently, dedicated scientists rather than, say, factory drudges. The monetary value of the facility is mentioned but not in terms of profitability. There isn't any poverty to be seen, or much in the way of class. There are certainly no drastic social divisions. There is xenophobia and prejudice but these are treated as human traits - related, if anything, to our biology - rather than social phenomena. Capitalism is hardly hinted at, economically or culturally. There is simply the world as it stands, as a backdrop to events. All of this broadly holds true for 'Ambassadors of Death' too. There are no tentacles in either story, though there is some mildly Weird inflection detectable in 'Ambassadors', in the appearance of the aliens and their peculiar ship. It's worth noting, in this connection, that an attempt is made to commodify the alien ambassadors, whereas this is not the case with the Silurians.
In 'Inferno', fascism (or some form of totalitarianism at any rate) is a major theme, but there's no hint in the text that it's linked to economics. This is not fascism as a form of ultra-statist reactionary capitalism, nor is it communism in the economic sense either! There are slaves in the alt world but slaves are not proletarians. Hierarchy is in evidence, even in the non-totalitarian version of reality, but strict adherence to hierarchies is made a pathology of Stahlman's own. Beyond the government's stated desire for a cheap new energy source, there's hardly a hint of economics. No capitalism to speak of. And no tentacles.
In 'Mind of Evil', people in prison are bad because they've got badness in their brains. The implications are, on the face of it, as biologically determinist as those hinted at in 'The Silurians'. Nuclear weapons are simply an expression of this badness in a generalized form. In its concentrated form (i.e. in working class thugs) it manifests as violent crime. Crime is disobedience to the 'law and order' of the apparently functionalist 'honest broker' state. In its general form, as it lurks in the heart of man, this innate darkness takes the form of warheads, which seem to be emblems of human 'folly' rather than of imperialism. Indeed, the American Ambassador is an innocent victim of the Red Menace and any mention of imperialism is mere Stalinist flim-flam for the Brigadier to smirk at knowingly. No private companies, no profits, no interest in commodification. And no tentacles.
In 'The Sea Devils', there's a cowardly, xenophobic and bellicose parliamentary private secretary (the show seems to find it particularly sinister that he eats toast as he orders bombardments) but he's clearly the exception to the rule. Every other establishment figure in this is either a stiff-upper-lipped straight-arrow or a well-meaning dupe. Hierarchy seems to function beautifully for everyone in this story. There's hardly a whisper about imperialism or capitalism. The Weird is often very maritime in its concerns (i.e. tentacles, crabs, etc.) but this story just looks like a Navy Recruitment film. No tentacles.
'Day of the Daleks' is a densely political text that needs a lot of unpacking... which I'll probably get around to one of these days. This is a story unusually aware of economics in the broad sense (i.e. how society is reproduced through production) and is certainly aware of the exploitation of labour... but the society of the future looks like Stalinism. Now... I'm personally persuaded that Stalinism (or 'really existing socialism' or 'communism', whatever...) was actually a bureaucratic form of state capitalism (I'm not in the SWP but I'm convinced they're broadly right on this). However, that idea was even less well known in 1972 than it is now, and a large majority of even the radical left at the time thought Russia and China were in some way socialist. Pertwee's barbed comments - particularly "Then why do they need so many people to keep them under control? Don't they like being happy and prosperous?" - seem to tally with the idea that this story is critiqueing 'communism', as does the concentration upon needing the cooperation of "the Chinese delegates".
Of course, we also have the guerillas who look like left-wing 'freedom fighters' - Shura seems to have deliberately styled himself after Che - and who are described as "fanatics" but who end up portrayed as (broadly) in the right. Even their assassination plan is not fully disdained in principle. But, the "third world war" seems to be something that nobody is responsible for, certainly not the well-meaning politicians. Imperialism hardly registers (except as Dalek conquest and as a clash between rival communist states, i.e. "troops are massing along the Russian and Chinese frontiers") and neither does capitalism. There are, you'll recall, no tentacles. Indeed, the story explicitly talks the talk of the gothic and hauntological. (All the stuff about ghosts.)
The Earth Empire in 'The Mutants' is only very distantly capitalist. There is some talk about exploitation (of Solonians and their minerals) but there's no indication that this is anything but straightforward military theft, as in ancient Rome. No tentacles.
And so on. You get the idea, I'm sure.
What's Good For IMC...
"Ah ha!" I hear you cry, "there should be tentacles in 'Colony in Space', surely - if his bullshit theory is correct!"
Well, firstly, remember that I've never claimed that tentacles appear every time capitalism comes up, only that they tend to when the show veers towards potential systemic critique of capitalism. But doesn't 'Colony in Space' qualify? Not really, because the story is essentially a liberal complaint about corporations, not capitalism as a system. IMC is strongly implied to be acting illegally and most of the colonists are surprised by their out-and-out gangsterism. The law is also implied to be relatively impartial, with most of the colonists seemingly having realistic hopes that the state will act for the best and arbitrate between competing claims.
More broadly, 'Colony' embraces certain bourgeois ideas about individual freedom and the 'progress' of Western civilization. It subjects the notion of technological and social progress to some sceptical questioning, but ultimately its qualms seem to be about 'technology' and warlike aims rather than capitalist industry per se. The commodity sought by IMC - duralinium - has none of the qualities that marked out Nestene plastic or Axonite as representing the commodity form as a concept or as capital itself.
Also, the story completely fails to notice that the colonists are encroaching upon a world that is already inhabited. In all the bickering between them and IMC, nobody stops to question that one or other group has the right to appropriate the planet and expropriate the 'primitives'. This is a liberal whinge about unscrupulous corporations bullying petit bourgeois small-holding colonials. It assumes the possibility of a just settlement between the claims of business and the rights of individuals. Law and order can be achieved when the excesses of one rogue corporation are curtailed. The right of colonists to impose colonialism upon natives is left unquestioned.
There is no more threat of a systemic critique of capitalism here than there is in your average Bond film.
The Quasi-Skulltopus and the Road Away from Serfdom (Not)
This is also true of 'The Curse of Peladon', and yet that has tentacles in it (sort of)... which demands explanation.
As in 'The Creature from the Pit' much later, the decidedly feudal nature of Peladon implies that the new system brought by the alien vistors is probably going to be, in some sense, capitalism. Sure enough, the entry of Peladon into the Federation will entail Federation exploitation of Peladon for minerals... i.e. industrial exploitation, mining, refining, export, etc. Arcturus makes a deal for Peladon's minerals with Hepesh because his own planet lacks them, and, in so doing, makes the minerals into commodities, although money is not mentioned (not even obliquely) so it's still only an implication. Guess what... Arcturus is a bit tentacular. Of course, so is Centauri... but then we all know the 'Federation' is meant to represent the Common Market. To put it crudely: s/he's got the good tentacles of free trade and he (Arcturus) has the bad tentacles of restricted markets.
Thing is... Arcturus is also a bit like a skull.
He's actually very nearly a skulltopus.
I suppose this is allowed because, in 'Curse', the tentacular has lost all traces of its old Weird charge, its unprecedented, meaningless incomprehensibility. It's become a sign detached from its previous associations outside Who. Even Terry Nation's plot-device monster, the Mire Beast, is more related to the Weird via its incongruousness and arbitrariness.
What we're seeing in 'Curse' is the first evidence that the show has started to habitually associate tentacles with capitalism, even though it originally invoked them in order to obscure it. What started as an evasion is becoming an established signifier, to be used even when capitalism is implied and characterized as bringing progress, cultural advancement, cosmopolitanism and liberalization. In 'Curse', the tentacular is reappearing because capitalism is heralded, even if only by heavy implication. Arcturus and Centauri represent the Federation, and the Federation is the onrush of trade and modernization and 'development' that is coming to disrupt the old ways and - we are asked to take this on faith - remake Peladon for the better.
There is no need to obfuscate the point at which the story's themes converge upon heavily-implied capitalism because capitalism is here heavily-implied to be the solution rather than the problem. The whole point of the story is to point out that silly, old-fashioned, class-ridden Britain, littered with the relics of a feudal past, should and must embrace the free trade future. The new system is better for all, except when it is hijacked by a corrupt, warlike, criminal reactionary like Arcturus. This is essentially the exact same bourgeois liberal message offered by the sequel, 'Monster of Peladon': sort out the reactionary isolationist clock-stoppers and any conspiratorial protectionists (and, in 'Monster', the loony left who incite the idiotic workers) and capitalism works like a charm.
In the 'Peladon' stories, the tentacles straightforwardly ride in on the back of their past association with capitalism. They do not obscure, they signify. Arcturus has them because he is part of the system. But he is also very-nearly a skull because, in 'Curse', the overtly gothic is being used to represent the old ways, and Arcturus is a drag factor - a protectionist, market-cornering, monopolist reactionary - who might threaten to pull Peladon back into hopeless feudalism. Indeed, he is directly conspiring with Hepesh to achieve just this aim. Arcturus and Hepesh want the same thing. They want Peladon to stay an undeveloped backwater. What Hepesh does not see - and Arcturus does - is that keeping Peladon out of the galactic Common Market is only possible by keeping it as a powerless and exploited client state to a foreign monopolist.
In the semiotic schema of the Peladon tales, the gothic is used to express everything that is abhorrent or pitiful under the liberal free-trade ideological assumptions. Aggedor haunts a torch-lit castle because we are being asked to contemplate a society stuck in the past. Arcturus is a quasi-skull because he too is a force of reaction, a block to progress. He has tentacles because Doctor Who is starting to associate tentacles with what, in this story, is the system of the future. This is not the Weird fused with the gothic. This is the gothic, fused into Doctor Who's emergent internal system of signs, juggling different forms of capitalism.