Episode 235: Deep-Sea Squid

Sign up for our mailing list! We also have t-shirts and mugs with our logo! This week we visit the weirdest squid in the deep sea! I was a guest on Tim Mendees's After Hours that's now up on YouTube! It's mostly about my writing but we talk about all kinds of stuff, including cephalopods! There is some bad language but it's not all that bad and it's mostly toward the end. Further reading/watching: Elusive Long-Tailed Squid Captured on Film for First time See Strange Squid Filmed in the Wild for the First Time (ram's horn squid) Multiple observations of Bigfin Squid (Magnapinna sp.) in the Great Australian Bight reveal distribution patterns, morphological characteristics, and rarely seen behaviour Untangling the Long-Armed Mystery of the Bigfin Squid Drawing of a long-arm squid and an actual long-arm squid: Asperoteuthis mangoldae, which really should be called the long-tailed squid:   Verany's long-armed squid, with its tentacles mostly retracted (so not looking very long-armed): Verany's long-armed squid with tentacles extended: Drawing of a paralarval Verany's long-armed squid: The ram's horn squid, floating along doop doop doop: Drawing of the coiled internal shell of the ram's horn squid: A clawed armhook squid mama with her egg cluster: Bigfin squid! Another bigfin squid! Good grief look at that! Show transcript: Welcome to Strange Animals Podcast. I’m your host, Kate Shaw. Before we get started, a quick announcement that I was a guest on a YouTube show called After Hours recently! I was there mostly to talk about my writing, but naturally animals came up too, especially cephalopods. There’s a link in the show notes if you want to watch the show. There is a little bad language, but not too bad and it’s more toward the end. Anyway, in a not-exactly coincidence, this week we’re going to look at some of the weirdest deep-sea squids known. Yes, weirder than the flying squid we talked about in episode 101. We don’t know much about any of them, but they’re definitely not what you expect when you think about squid. Let’s talk first about Asperoteuthis acanthoderma, the long-arm squid. It’s also sometimes called the thorny whiplash squid because it has little pointy tubercules in its skin and long, whiplike feeding tentacles. It lives in the deep sea and has been found in both the Pacific and the Atlantic Oceans, although very rarely. Despite its name, its feeding tentacles are much longer than its arms, although its arms are pretty long too. A squid’s body is generally more or less torpedo-shaped and is called a mantle. It has eight arms and two feeding tentacles that are usually longer than the arms. Many squid species have relatively short arms compared to mantle length. The feeding tentacles in long-arm squid are very slender and delicate, and they’re easily broken off after the animal dies and has washed around in the water for a while. One intact specimen has been found and measured, though. It had a mantle length of almost a foot and a half long, or 45 cm, but its total length, including the tentacles, was 18 feet, or 5.5 meters. The tentacles were 12 times the mantle length. Using that ratio, one large specimen found in 2007, which was 6 1/2 feet long, or 2 meters, including both mantle and arms, is estimated to have measured up to 24 feet long when it was alive, or over 7 meters. Most of its length is due to its incredibly long, thin feeding tentacles. So what does the long-arm squid eat with those long, delicate tentacles? We don’t know. We don’t know most things about the long-arm squid. Another species of Asperoteuthis is Asperoteuthis mangoldae. So little is known about it that it doesn’t even have an informal name. It was only described in 2007 and has only been found around the Hawaiian islands in the Pacific Ocean. It looks similar to the closely-related long-arm squid but without the incredibly long feeding tentacles. Instead, it has a sort of tail, so I nominate it to be called the long-tailed squid. It was caught on video for the first time in 2019 by a deep-sea rover. You’re going to hear a lot about deep-sea rovers in this episode. There are lots of links in the show notes to articles with embedded video of various squids, which is really interesting to watch. Asperoteuthis mangoldae is a long, slender squid. I couldn’t find any measurements so it could be that’s just not known right now. The species in this genus have an extension of the mantle, on the side opposite of the arms, that looks like an extra fin but that doesn’t seem to be used as a fin. In the long-tailed squid, this extra fin is as long as its mantle and arms and feeding tentacles all measured together. Most of the time the thin flaps of skin on either side of the so-called tail are extended, making it look like a really long fin, but when the squid feels threatened and needs to flee, it collapses the fin part around the middle section so that it reduces drag in the water. That way the squid can move faster. Researchers speculate that the tail section may make the squid look much larger to potential predators, and possibly may imitate an organism called a siphonophore that has stinging cells. Another squid called Verany’s long-armed squid is Chiroteuthis veranii. It’s related to the long-arm squid we talked about at the beginning of the episode, but they’re placed in different genera. It lives throughout the world’s oceans, often in the deep sea although not as deep as some of the species we’re talking about today. Unlike most squid, whose arms are all about the same length, two of its arms are much wider and longer than the others. Like the other long-arm squid, its feeding tentacles are incredibly long and thin. The mantle is quite small, up to 8 inches long, or 20 cm, with the legs about the same length as or a little longer than the mantle, but the total length of this squid, including the feeding tentacles, is over four feet, or 130 centimeters. Most of the time the feeding tentacles are retracted, though, so they’re no longer than the arms, and they’re protected by the two largest arms. When the squid sees a tiny fish or crab or other small animal it wants to eat, it can shoot its retracted tentacles out at high speed to catch it. It’s probable that other species of long-armed squid hunt the same way. A squid’s eggs hatch into an initial form called a paralarva. This is actually the case for other cephalopods too, including octopuses. The paralarvae usually just look like teeny-tiny miniature versions of the adult, but with stubby little arms. In the case of Verany’s long-armed squid, though, the larval squid looks sort of like a little rod. It’s long and thin, mostly transparent, and has a gladius, also called a pen, that sticks out the end of the mantle on the opposite side from the arms. The pen of a squid is named after an ink pen, although the other name, gladius, refers to the shape of a type of ancient Roman sword. It’s a vestigial shell but located inside the squid’s body. The tail of the long-tailed squid we just talked about is given structure by the gladius, so it’s possible that its paralarvae look rod-like, like those of Verany’s long-armed squid. Speaking of internal shells, the ram’s horn squid has a coiled internal shell. This is unique among all the squid known to be alive today, so the ram’s horn squid is the only living member of its own order and its own family and its own genus. Technically it’s not really considered a squid although it is a closely related cephalopod. It’s small, with a mantle length only about an inch and a half long, or 4.5 centimeters. Its eight arms are quite short and it has two feeding tentacles that are about the same length as its mantle. Its mantle has an outer covering that extends down almost to the squid’s eyes, and it’s big enough that the squid can pull its eyes and legs and tentacles under this covering. The spiral shell resembles that of a nautilus, but it’s inside the squid instead of the nautilus living inside the shell. The shell contains gas that the squid uses to adjust its buoyancy. For a long time researchers were confused as to how the ram’s horn squid oriented itself in the water. The empty shells from dead squid wash ashore pretty often, and experiments with them show that they want to float with the big end of the shell pointing downward. That confused the researchers, since that would mean the squid floats around with its arms downward too, which means that the photophore on the tail end of its mantle points upward. A photophore is a light-emitting organ, which is common in deep-sea animals. Usually an animal wants its light to point downwards, which means that larger animals looking up toward the surface see a little light sparkling amid the light shining down from the surface instead of seeing a squid-shaped shadow against the surface. Then, in late 2020, a deep-sea rover exploring the northern section of the Great Barrier Reef off the coast of Australia got a video of a ram’s horn squid in the water. It was the first time a living one had ever been observed. In the video, the squid is floating with its arms pointing upward, flapping the fins on its mantle to move along in the water. Mystery solved! There’s still a lot we don’t know about the ram’s horn squid, but at least we know it doesn’t swim around upside-down. Another squid that has only recently been seen alive in the wild from a deep-sea rover is the clawed armhook squid. My brother Richard alerted me to this one in a Twitter thread. The clawed armhook squid lives in the northern Pacific Ocean and has a mantle length of about seven inches, or 18 cm. Its arms are about the same length as its mantle. It gets its name from the female, which has small hooks on her arms to help her keep hold of her egg cluster. She lays about 3,...