Despite their weirdness, they have more or less the same muscles we do. In fact, most animals do. The same familiar muscle structure can be seen throughout mammals, birds, reptiles and amphibians.
Behold the nightmarish beak of a female colossal squid, one that weighed 770 lbs, measured nearly 11.5 feet long and had eyes nearly 14 inches in diameter. It was the second only intact colossal squid specimen ever recovered.
The difference is cephalopod arms have suckers all the way along their length, but tentacles only have suckers at the end (except for nautilus tentacles, which have no suckers).
Arm:
Tentacle:
So octopus have 8 arms and no tentacles, squid and cuttlefish have 8 arms and 2 tentacles (except female cuttlefish, which have 6 arms), and nautilus have around 90 tentacles and no arms.
I received this question today, I have to say this puzzled me the whole day. Let’s delve into the subject I never thought I would delve in: cephalopod jaw evolution!
Behold, the beak of a very large species of squid. Some people use it as the perfect example of convergent evolution: both birds as well as cephalopods developed a sturdy beak to crack hard materials (e.g. nuts, shells or crabs). But to be quite honest, the evolution and possible precursor of the cephalopod jaws have puzzled scientists for ages.
Beak of a freshly caught squid. Royal society of Chemistry; Photographer: Mark Conlin
Let’s first address the elephant in the room, the squid jaws are not homologous with the radula we know from snails. Even more interesting, squid, octopi and cuttlefish even have a tongue-like radula behind the two jaws to scrape the flesh of their prey. But if the jaws are not a derived form of the radula, what are they derived from?
Let’s say you’re a cephalopod in the late Jurassic period, the sea is full of predators and you need to protect yourself. You have your hard shell, but the predators can just get in there through the front door. Thank your ancestors, because you have what you call an operculum, a hard plate you can use to close your shell. Dzik describes the evolution of the cephalopod operculum in detail as part of his thesis in 1981. Here he explains, based on fossils and previous findings by other authors, that the operculum in the “Hypothetical ancestor of all shelled mollusks (Coniconchia)” can also be found in the most basal groups of cephalopods (Endoceratida):
Evolutionary relationships between main groups of early Cephalopods, with medial sections and apertural views of all groups. Dzik, 1981
In more derived groups, something interesting happened: the operculum splits in two parts, in structures we call the Aptychi. During evolution, the aptychi migrated deeper inside the body, but could still be pushed to the outside to act as an operculum. While the aptychi are retracted, the pointy ends emerged a little and could be used as some way to destroy sturdy preys, like shelled invertebrates, thus functioning like mandibles or real “jaws”.
Some examples of aptychi (top right: Oppelia from Late Jurassic of Solnhofen, Germany; bottom left: aptychi (recto and versus) from Late Jurassic of Lombardy, Italy), and conceptual scheme of their function if indeed they were used to close the shell aperture, as opposed to being jaws. Wikipedia commons; Antonov
Aptychi are often found inside the shell of ammonoids, together with a single plate, what we call an Anaptychus. The function of the Anaptychus, closing the upper part of the shell-opening, can still be found in extant nautili (Nautilus sp.), where a leathery flap closes the shell. It is believed that modern day cephalopods simply removed the problem of protecting the shell entrance by having new structures take care of that (like in the case of the nautilus), or by just loosing the shell partially (e.g. cuttlefish, squid) or even entirely (octopi).
The diet of extinct cephalopods cannot easily be studied, so we cannot be totally sure on where the closing-hatches were used for. For now, this sounds like the most plausible explanation, but there’s still a lot to be discovered.
i used to think the brain was the most important part of the body. then I thought, look who’s telling me that…
In the human body, there are SEVEN WOEFUL PRINCES that suffer under the harsh lash of REALITY-CONQUERING TYRANT CEREBELLUM. Their names are thus:
ARTERY-AND-VEIN MENDICANT: The prince who sits at the center of an endless ocean of blood, stirring the systolic and diastolic tides with his jade-lacquered oar. It is said that in ancient times, he sat the throne of selfdom, but was usurped. It wouldn’t be very mendicantly of him to pursue a devil’s urge to vengeance and retribution, but even the greatest saints can have slight flaws in their character.
BRAZEN LIVER CHAMPION: Only the strongest may survive in the terrifying princedom of the BRAZEN LIVER CHAMPION, a behemoth warrior clad head-to-toe in superheavy membraneous armor. He seeks to build up an army of deadly toxins and warrior-cells with which to overthrow the reign of REALITY-CONQUERING TYRANT CEREBELLUM, wresting the throne away for himself.
CANDLEMAKER: She who keeps the lipids of the body in her magical jar, and fashions fat into candles that burn with all the energy stored within it. She keeps no royal domain, but has declared the Cellular Republic of the Tissues, a neutral ground of function anarchy where princeless organelles or exiled traitors may make their homes. Still, she schemes for the throne of selfhood, for she dreams of transforming the body into an existence of pure energy.
DEVILISH APPENDIX LORD: Of the SEVEN WOEFUL PRINCES, the DEVILISH APPENDIX LORD is the most woeful by far. They exist as nullity, a collection of emergent processes of the void that have concatenated into a capacity for experiencing reality. Every day, the DEVILISH APPENDIX LORD must choose between continuing the endless torments of existence, or returning to their kingdoms of nothingness by killing the body whole. How long can such patience last?
GODFUCK LIBIDO: This prince is a wild beast among nobles, in the sense that it is literally a big fuck-off bear with magic powers. It governs the junk, and all the dumb animal impulses that emanate from within. GODFUCK LIBIDO has no plan for what it’d do if it won the throne of selfhood, because bears are not capable of that kind of long-term thinking.
KALEIDOSCOPIC PINEAL DRACULA: The vampire prince reigns from a petrified cathedral within the very flesh of the REALITY-CONQUERING TYRANT, holding her dominion against the tyrant’s absolute rule by the power of her three vampiric eyes. Within the bounds of her demesne, she keeps a ruthless court of scheming neurotransmitters, hormone functionaries, and the tyrant’s own emissaries. She would take no throne for herself, but rather push the body onward to full revolution, allowing a transcendent evolution towards the end of human entelechy through the harmonious alignment of all organs and tissues. But then again, she is basically a fucked-up dracula, so, take that last part with a bit of salt.
LOVELY LADY FEMUR: This skeleton empress commands all manner of necromancy, reigning from an ivory tower that binds the human body to the dirt of its mortality. If she were to the steal the throne of selfdom from the REALITY-CONQUERING TYRANT, her magical power would suffuse and transform the body.
Anonymous
