Ram’s Horn Squid Profile
Cephalopod evolution truly is a lost epic, the middle of which includes 360 million years of head-leg supremacy in the oceans.
When the asteroid hit, the few that survived lurked in the safety of the deep and became what we now recognise as squid, octopus and cuttlefish. As well as a cluster of other groups, lesser-known representatives of an otherwise extinct lineage.
One of these is the Ram’s Horn squid, named for the little floaty horns that wash up on beaches after they die. Except, it’s not a squid, and these aren’t horns. They’re shells, internalised over so many years like the trauma from the cancellation of the Pirates of Dark Water. And like the best cartoon ever made, the full story of the ram’s horn squid remains a marine mystery.
Ram’s Horn Squid Facts Overview
| Habitat: | Oceanic island waters |
| Location: | Tropical and Subtropical waters worldwide, some temperate regions |
| Lifespan: | Unknown |
| Size: | Up to 45mm (1.8 inches) |
| Weight: | Nor reported |
| Colour: | Reddish-brown |
| Diet: | Small fish, crustaceans, echinoderms, cnidarians and other marine invertebrates |
| Predators: | Birds, predatory fish, swordfish, whales |
| Top Speed: | Unknown, can descend quicky when upset |
| No. of Species: | 1 |
| Conservation Status: | Least Concern (IUCN) |
Ram’s horn squid are one of the multitudes of cephalopod orders not represented in mainstream media or the culinary arts. But they’re just as important to the seafood industry by being the top food of swordfish.
Yet, there’s so much more to them. These little mysteries have a tail light and a very advanced buoyancy aid, which they use to stay more or less out of human perception, making their true lives a bit secret.
Interesting Ram’s Horn Squid Facts
1. They’re not squid
Everyone knows about squid and octopus, and most will know what a cuttlefish is. The somewhat lesser-known nautilus is a fourth type of cephalopod that looks more like a snail, and that’s generally where we stop being able to name orders.
But there are quite a few other cephalopods in the ocean that don’t fit into these groups.
Many are pretty squid-like and their common names reflect this. And so it is, the Ram’s horn “squid” is more closely related to a cuttlefish than a squid (though it’s not a cuttlefish either), and is the only member of its order left.
It’s named “squid” because it looks like a squid. And the ram’s horn bit comes from a fascinating organ it keeps well hidden.
2. They have a shell
Almost all molluscs have shells, and cephalopods are no exception. Well, most of them. Once upon a time, all of them did. Then some started wrapping their little flaps around the shell and eventually, many shells evolved to be entirely inside the mantle.
Of the cephalopods today, only the Nautilids have external shells, but others have theirs inside.
If you’ve ever owned a budgie, you might have fed it what’s left of the internalised cuttlefish shell. Octopuses have tiny fragments left of theirs and true squid have turned theirs into a thin strip of flexible, but rigid protein.
Likewise, the shell of the ram’s horn is fully inside it, but what makes this one so special is that it maintains its snail-like shape. Inside this little cephalopod is a perfect, segmented ‘snail’ shell, coiled like its namesake. 1
3. The shell is a flotation device
This shell is more complex than the gladius of the squid, or the cuttlebone you feed your bird. It’s a functional shell, in that it has a series of chambers. Somewhere between 25 and 37, to be imprecise.
Between the chambers runs a siphuncle, which, as well as being a fantastic word, is a shelled cephalopod’s connective tube that runs between the chambers and allows them to be evacuated or flooded as needed.
(Incidentally, a cuttlefish shell might not be quite as complex, but still works in a similar fashion).
Usually, this orients the ram’s horn in a face-down position in the water column and can be used to raise them up or drop them down on a whim. 2
4. Tail-light squid
If the face is down, the tail must be up, and this ‘pod has a little extra in the back. Between its fins, there’s a special glandular organ that emits a green light.
Getting a green on this posterior might suggest something to do with mating, but in this animal, it doesn’t appear to be related to that; at least, as far as we can tell.
Instead, its thought that the light offers a counter-illumination strategy, which brings the glow of the cephalopod up to the same brightness of the dim ambient light. Essentially, counter-illumination removes the shadow or silhouette of an animal.
But this would only make sense if the animal was oriented the other way around, and this is how it’s seen on some of the rare footage gathered of it.
As it happens, we are still struggling to piece together the mysteries of this little creature. 3
5. We don’t know much about them
These cephalopods avoided multiple catastrophic events, including the most recent that wiped out the non-avian dinosaurs. And as a whole, it appears this strategy is working for them during the ongoing human-caused mass extinction event too.
They are well hidden in the deep ocean and prefer to keep it that way, and as such, we know very little anything about their breeding, their social structure, or how they communicate with one another.
It’s thought that their light organ might be used in communication between conspecifics, but this has never been witnessed.
6. They have an effect on the swordfish market
Far too often, what we know and how we talk about animals in the ocean is in the context of how it affects the economy of the international seafood industry. And as it happens, it’s true here, too.
While we don’t know exactly the range of animals that predate upon these little cephalopods, we do know that they’re one of the major food groups for one of the ocean’s coolest bony fish predators: the swordfish.
These swashbuckling, calamari-guzzling sushi rolls are so fond of Ram’s horn squid that their populations are noticeably impacted by the presence of the cephalopod, which might be good news for the latter since there’s a lot of money to be made from swordfish, so there is an incentive to keep the ram’s horn from disappearing, too!
Ram’s Horn Squid Fact-File Summary
Scientific Classification
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Cephalopoda |
| Order: | Spirulida |
| Family: | Spirulidae |
| Family: | Spirula |
| Family: | spirula |
Fact Sources & References
- Laura Geggel (2017), “Why the Octopus Lost Its Shell”, Live Science.
- “Spirula spirula”, Animal Diversity Web.
- Dante Fenolio (2018), “A Ram’s Horn squid (Spirula spirula) trawled from between 200 meters depth and the surface, Gulf of Mexico”, Jungle Dragon.