ZeFrank appears to have invited himself on a virtual NOAA (National Oceanic and Atmospheric Administration) “deep dive” from the Okeanos Explorer, a research ship that has a remotely operated vehicle (ROV) that can descend to 6,000 meters. A variety of videos reside on the NOAA website, and I suspect that ZeFrank took the video, with permission, from the site.
The goals of the Ocean Exploration mission are these:
With the mission to explore the ocean for national benefit, NOAA Ocean Exploration is the only U.S. federal organization dedicated to exploring the deep ocean. We are filling gaps in the basic understanding of U.S. deep waters and the seafloor and delivering the ocean information needed to strengthen the economy, health, and security of the United States.
The “conversation” you hear is the narration of the original videos combined with voiceover from ZeFrank, creating a “dialogue” between him and the Explorer personnel. Regardless, you’re here for the weird creatures that live in the depths of the ocean.
Send those photos in, please! We’re running low. Before we start, can anyone identify this raptor that perched over Botany Pond yesterday? The ducks were upset, quacked, and then formed a pack in the pond and remained very still. I took a photo, but it was hard because the bird was high up in a tree above the pond. So far we’ve never had a raptor attack a duck or duckling, but the adults still get freaked out when they see one.
Today we have a melange of California photos from Joe Dickinson. Joe’s captions are indented, and you can enlarge the photos by clicking on them.
Thanks to a slew of readers, we have enough photos for several potpourri features, but do send in your long-form contributions when you can. Thanks!
We’ll have two contributors today, the first being physicist and origami master Robert Lang from Altadena, California. Like all photos below, the captions are indented and you can enlarge the pictures by clicking on them:
I saw today you asked for a few topping-off photos, so I thought I’d send the below, from recent mornings’ hikes.
First, we have the common American Crow (Corvus brachyrhynchos). A group of these started hanging around my place for a few days; I suspect, coincidentally (and sadly) with the disappearance of the contents of a mourning dove nest I’d been monitoring in a nook above the back porch.
And now for a few hiking photos. The Whipple Yucca (Hesperoyucca whipplei) blooms in June, studding the mountains with cream-colored candlesticks. They bloom only once, then die, but there’s plenty of slightly younger ones to fill in each year.
Darkling Beetles (Eleodes sp., possibly armata) are fairly common around here. When disturbed, they stick their butt up in the air. This one was just going about its business.
And last, a new and uncommon critter: the Southern California legless lizard (Anniella stebbinsi). At first glance I thought it was an earthworm from its size and shape and the way it was twitching from side to side, but given the heat and dryness, any earthworm wouldn’t have been long for the world! A closer look revealed its reptilian scales, and then its stumpy tail and lizard-like head helped narrow it down.
Here are two photos by regular Joe Dickinson. He didn’t supply the IDs, but it’s clear that one is a flying fox and the other a primate. I’ll add the IDs when he responds to my query. In the meantime, you can guess!
Please send in your photos. I will probably put this feature on hold while I’m in Texas, but, except when I’m gone, the tank is always emptying.
Today’s photos come from regular Tony Eales, an anthropologist in Queensland who loves natural history. Tony’s captions and IDs are indented, and you can enlarge his photos by clicking on them.
Tropical North Queensland part II (part I is here)
Here are a few of the other wonderful organisms I encountered on my brief trip up north to the jungles.
Australian Prismatic Slug (Atopos cf australis). I’m pretty sure there are several species of this slug around, but they all seem to be labelled A. australis. They are predatory slusg with curved teeth in the radula, and they spit acid onto snail shells to help rasp through to the snail inside.
The tracks at Speewah Conservation Park were empty of other humans, which was great for spotting wildlife. I got to approach this Northern Tree Snake (Dendrelaphis calligaster) quite closely without alarming it too much. It’s a slightly built rear-fanged colubrid and presents no danger to humans.
These beautiful Tropical Rockmasters (Diphlebia euphoeoides), a type of flat-wing damselfly, were common around Cairns and the surrounding area. I wish we had such beauties near me. This photo shows a male and female at Lake Eacham.
This is a lichen-mimicking caterpillar, Enispa prolectus. These caterpillars fasten small pieces of lichen to their backs with silk as a form of camouflage.
As the area is a tropical rainforest and it was actually raining while I was there, I was inevitably attacked by many, many leeches. However, I spotted this one (Haemadipsa sp.) on a railing at night actively questing, and I was struck by the bright colours. I have to wonder, are these colours signals to each other, warning, camouflage or just random?
One for Mark Sturtevant: a Pisuarid spider, related to the Dolomedes triton that he featured recently. This one is Hygropoda lineata. These were very common in the north. Rather than living by the water, these spiders make a simple web platform across the surface of broad leaves and sit on top of it, often looking like they are hovering in thin air.
Nephila pilipes, the Giant Golden Orbweaver. These are well named. We have Golden Orbweavers at home, which are big spiders, but these northern ones are mind bending. This one had a body length of about 50mm and was eating a cicada the size of my thumb. The span of the web was about 6 metres from attachment to attachment and the main orb about a metre and a half across.
They are only weakly venomous to humans and very reluctant to bite even when handled, preferring just to climb away.
There were a huge variety of amazing ant species to be found in the forests, but by far the most common were the Green Weaver Ants,Oecophylla smaragdina. I was always checking their trails for signs of the spiders that mimic them. Unfortunately, I didn’t find any. I did however observe their interesting behaviour of holding leaves together like living stitches. Inside the ball of leaves larvae are being hatched. The larvae are then taken by workers and produce silk to tie the leaves together more permanently.
In Speewah Conservation Park there were lots of climbing palms, Calamus caryotoides. The mature stems are festooned with black spines to ward off herbivores. However, these caterpillars, which I’ve yet to ID, use the spines to create a protective home as the crawl around and eat the leaves.
These long-jawed orbweavers, Tetragnatha rubriventris, were very common around Cairns. They have massive hinged chelicerae and the males have large clubbed pedipalps with complicated spiralled spines for placing a sperm packet into the female epigynum. all this weirdness makes them great photo subjects for a really alien look.
Also in Speewah Conservation Park I found this amazing fruiting bodies of the slime mould Tubifera microsperma.
Imagine if Robespierre, after being guillotined during the Terror in France, was able to regrow his entire body just from his head alone. Well, that’s the equivalent of what some sea slugs can do, as reported in the new issue of Current Biology (click on screenshot below to access article, pdf here, and reference at the bottom).
In fact, two species of sacoglossan sea slugs, members of a group of shell-less mollusks, can not only grow a new body from just the head, but can do it twice in a row. Amazingly, the body that gets regrown includes the heart and the digestive system, which makes one wonder: how can they regrow a whole body without the nutrients gleaned from digestion? And how can the head live without a heart to supply it with oxygen. Well, that’s part of a very cool story.
Two Japanese researchers found that a substantial proportion (33%) of two species of sea slugs (Elysia cf. marginata and E. atroviridis) were observed in the laboratory to shed their own heads (“autotomy”, a fancy word for “self amputation”). Moreover, the heads regenerated new bodies—and quite quickly: within 20 days or so. The shed bodies, which did not regenerate new heads but died, contained the heart and the digestive systems. The heads, meanwhile, closed the wound after “voluntary” separation, began nibbling on algae within hours, and the regeneration of the entire body was done within three weeks.
Here’s a shot of four phases of the autotomy from the paper (as is the caption):
A) Head and body of Elysia cf. marginata (individual no. 1) just after autotomy (day 0), with the pericardium (heart) remaining in body section (arrow). (B) day 7, (C) day 14, (D) day 22, showing whole-body regeneration.
The 10 mm scale bar is about 0.4 inches. By day 22 they’re fully whole again, with a beating heart and a digestive system. See the green color? Those are algae that live in the mollusk’s cells: a key to how they might get the energy to regenerate.
Here’s a tweet with a video of the separated head and body. It’s just bizarre!
But wait! There’s more! The authors collected 82 sea slugs from the ocean that were all parasitized by the copepod Arthurius, which lives in the body (not the head) and inhibits the sea slug’s reproduction. Many of the parasitized slugs got rid of their bodies when brought to the lab. Here’s the parasite:
This gives a clue as to why they’re ditching their bodies: to get rid of a parasite that lives in the body and impedes reproduction of the sea slug. Thus, it might be adaptive to discard your body along with a parasite, even if it takes substantial energy to regrow a new body.
Of 82 parasitized individuals collected from the wild, 41 shed their bodies. Of these, 13 regenerated those bodies, but the rest died. So there’s no guarantee that you’ll survive if you shed your parasite-laden body. But if you’re permanently sterilized by the parasite, or your reproduction is severely reduced, it may still be adaptive to take the chances and break apart; your net fitness may be higher that way. After all, the regenerated bodies, lacking parasites, are perfectly fertile.
More indication that this trait is adaptive is that these sea slugs have a “transverse groove” at their neck—the line where the breakage occurs. This implies that parasitism and body-shedding was a regular feature of the sea slugs’ past. Here’s the groove, which you can see if you look closely:
When the authors tied nylon string around the groove, the slugs broke apart at this position, shedding a body that represents 80-85% of their total weight. When mock predator attacks took place, however, like pinching the head and cutting parts of the body, they did not break apart. This suggests that autotomy, if it’s an adaptation, is an adaptation to get rid of parasites and not to escape predators. (Many animals shed body parts when attacked, like lizards and salamanders that drop their tail when a predator grabs it.)
One question remains: where do the severed heads get the energy to regenerate an expensive body? The answer is another fancy word: kleptoplasty. Here’s how the authors explain it:
Why these sacoglossans can regenerate their body even if they lose most organs remains unclear, but we suspect involvement of kleptoplasty. In Elysia, a highly branched digestive gland is spread over the majority of its body surface, including the head, and the gland is lined by cells that maintain ingested algal chloroplasts. Thus, these sacoglossans can obtain energy for survival and regeneration from photosynthesis by kleptoplasts, even when they cannot digest food.
My question in response to this is: “do they get everything they need to regrow a body from the algal chloroplasts, including amino acids, sugars, and fats?” I suspect they do: where else could they get them? But perhaps a little digestion occurs in the mouth as well.
Where does this fit into biology? The phenomenon of autotomy is well known, as is the ability of many animals to regrow lost parts (you may have done such an experiment with flatworms when you were in high school). What’s unusual here is the regeneration of the entire complex body after it’s jettisoned, including the heart, which you would think was needed to keep the head alive! The authors say this:
Both Elysia cf. marginata and E. atroviridis shed the main body, including the heart. Some other sea slugs also autotomise, but they shed minor body parts such as tails, parapodia, or dorsal papillae. Other invertebrates (e.g., cnidarians, planarians, and asteroids) can regenerate their main body following division. Also, some amphibians are known to have a high regeneration capacity, including tails, limbs, eyes, and even the heart ventricle. However, autotomy in this study is remarkable in that animals with complex body plans can survive even if they lose the main body, including the heart, and subsequently regenerate the whole lost area. The reason why the head can survive without the heart and other important organs is unclear. We have succeeded in a complete rearing of Elysia cf. marginata for multiple generations — thus, they can be used as a model system for studying autotomy and regeneration of the body.
Now it’s no surprise that the animal has the potential to regenerate the body: after all, every cell in a sea slug contains all the genetic information necessary to produce another entire sea slug. But the trick is how to mobilize that information, which is usually inactivated in the wrong parts of the body. (We don’t activate the genes producing a liver, for instance, where our heart is supposed to be.) Somehow there is a mechanism here that makes the regenerating cells totipotent: capable of producing any part of the body starting at time zero. If we could figure out how they do this, we might be able to do it to ourselves, regrowing lost or diseased organs. But that is pure speculation; after all, we are not invertebrates—except for George Bridges at The Evergreen State College.
There are two places on Earth that constitute Vast Unknowns with the potential for finding new species. One, the tropical rain forest, is relatively easy to access, but the area is so vast and difficult of access that there is much to be discovered. And of course the tree canopies, which are rich with life, are not so easy to access.
The other place is the deep sea, particularly around and below the Antarctic continent. A new paper from Frontiers in Marine Science (click on screenshot below, pdf here, full reference at bottom), describes a batch of organisms, some with stalks, clinging to a rock beneath an ice shelf attached to the land. The interesting part of this study is not only the existence of life deep below ice shelves (that’s been seen before, including observations of fish, worms, anemones and mollusks), but life so far away from the open sea. What the eight researchers found was a group of stalked and nonstalked sessile organisms, probably sponges, clinging to a small boulder resting on the sea floor. The boulder was 260 km (160 miles) in from the edge of the Ronne Ice Shelf. (A shorter piece in the Guardian is here.)
This means not only are there sessile, filter-feeding organisms living far away from where the food comes from, but, even more striking, the currents that could bring detritus and microorganisms to those sponges are not from the closest open ocean, but from the opposite direction, since that’s where the currents come from. Given these currents, food for the observed species probably comes from between 625 and 1500 km (388-932 miles) away: the nearest open ocean that constitutes the source of photosynthesis that ultimately yields all the food. The researchers couldn’t collect the species, for they can be observed only through small holes bored with hot water through the thick shelf. Further, the big rock to which the organisms were affixed is 1233 m (4045 feet) below the ice. Given their remoteness, it’s almost certain that these species are new to science.
What’s striking about all this is that the total area explored by many researchers under the vast Antarctic ice shelves, which are so hard to penetrate, is smaller than a tennis court! Imagine what’s under there! This, however, is the first time that any sessile (immobile) organisms have been found on a substrate below an ice shelf. The remaining organisms involved—and there’s a table of them in the paper—are mobile (i.e., fish) or live on a soft, sea-bottom substrate.
Click to read the paper; I’ve put some videos of what they saw in the tweets below.
Here are the two great Antarctic ice shelves: the Ross and the Ronne (11 o’clock at the top), with the map taken from the paper. The places where the shelves have been penetrated by boring are indicated with dots: filled black dots show sites that yielded observations of organisms, while the sites showing no life have open (white) circles. The one spot below the Ronne shelf that produced the sessile and stalked organisms in this study is marked with a yellow star.
The animals, which are likely to be sponges but could be some other sessile or stalked organisms like ascidians, barnacles, or even worms or cnidarians, were affixed to a “drop boulder” about 1 x 0.75 meters across. How did it get there? The term “drop boulder” is a clue: this was probably a rock from the mountains on the continent itself that found its way into glacial ice, and then moved onto the ice shelf. At some point it fell through the ice and onto the sea floor. It then—only Ceiling Cat knows how—got colonized from another site.
Here’s the figure from the paper showing the boulder and its affixed organisms. They’re not very clear, and they’ve had to outline and highlight the organisms. I’ve added the caption from the paper
Here are two videos, the first showing one of the scientists involved in the study explaining the find and its significance. The second video shows the organisms: the blobs on stocks are particularly clear. You can see the difficulties of trying to manipulate a probe and a light in the darkness through a borehole more than 4,000 feet above. But yes, those aren’t artifacts: they’re alive!
Discovery of life after drilling through 900m of Filchner-Ronne Ice Shelf in #Antarctica.
Another map shows the holes drilled in the immediate area and the direction of the sub-shelf currents in the vicinity. The hole that yielded the view of the boulder is FSW2. The black and purple arrows (see caption) indicate the direction of water flow, i.e., where the food comes from. As you see, the currents don’t flow from the nearest edge of the ice shelf but from a far greater distance, so the food particles have taken a circuitous route.
The upshot: This is only a preliminary observation, and we don’t even know what those bloody creatures hanging onto the boulder are. But even observing them is a hard job: you have to get yourself onto the ice shelf with all your gear (perhaps they flew in), and then use a hot-water boring system to get through the thick shelf ice and then go down nearly a mile. To find out what these species are, they’d have to collect them, and that would involve either devising a boring/collecting device, or getting some kind of submersible below the shelf, most likely from above, which itself is nearly impossible. Going in below the shelf from the sea is theoretically possible, but it’s a big distance!
At any rate, what we know is that there are certainly many unknown species beneath the shelf, and maybe even unknown phyla. And once again we get the lesson that life is extremely tough and tenacious, here living in total darkness in near-freezing waters about a mile down, in an area where food is pretty damn scarce.
Today’s lovely photos come from Tony Eales in Queensland, and are a potpourri of plants and animals. His captions are indented, and you can click on the photos to enlarge them.
I was recently in tropical north Queensland for work and decided to take a couple of days ‘time off in lieu’ that was owed me and visit the world heritage rainforests of the Atherton Tablelands.
Oh my ceiling cat! I managed to tick off three of my life-time bucket-list organisms in two days, along with many other amazing species which I’ll send in another email.
First the setting. I spent my days searching around the Lake Eacham National Park. The centrepiece of the park is a crater lake in an extinct volcanic caldera but I was told about an unsigned track down a closed road that went into the forest to some cascades on Wrights Creek that runs between Lake Eacham and Lake Barrine.
At night I went to Curtain Fig National Park, which is a small patch of primary forest just outside the little town of Yungaburra.
It was in this little forest that I saw my bucket-list creatures.
A Boyd’s Forest Dragon (Lophosaurus boydii). I was searching through hanging leaves at night looking for insects and spiders to photograph when I found myself almost eyeball to eyeball with this beautiful lizard.
Lucky too, for during the day they have a habit of moving around the tree trunk such that it is always between you and the lizard, thus you often pass them without ever knowing they are there.
The last night I was there I stayed in the forest on dusk, hoping to catch a glimpse of the Lumholtz’s Tree Kangaroos (Dendrolagus lumholtzi) that I knew lived there. I gave up and went back to town to sit by the Platypus viewing platform hoping I’d have better luck with the monotremes. There, right beside the main road in a tree next to the bridge, was a tree kangaroo.
And the most exciting for me though perhaps not for everyone, I saw my first Velvet Worm. I have a real thing for small phylum. These creatures have fascinated me ever since I learned of them in high school biology then later when they were featured in David Attenborough’s 2005 documentary Life in the Undergrowth. Now I have finally seen one I am not disappointed. They are amazing to watch move but I hope one day to see one take down prey.
This one is in the family Peripatopsidae or Southern Velvet Worms—the only Velvet Worm family in Australia.
I missed out on seeing the famous Stalk-eyed Flies in Borneo that are in the family Diopsidae. However, at Curtain Fig NP I was able to ‘next-best-thing’ it with Stalk-eyed Signal Flies (Achias sp.) in the family Platystomatidae. I was very pleased.
Keep those photos coming in! Today’s contribution is from a regular, Mark Sturtevant, who sends us a panoply of insects (and one arachnid). His notes are indented:
Here are pictures of insects that were taken during the previous summer.
The first pictures are of carpenter ants (looks like Camponotus pennsylvanicus) tending a colony of poplar tree aphids (Chaitophorus populicola). I think it is well known that ants can guard aphids, and feed on the sugary secretions that they supply in return. In the second picture you can see an ant give food to another.
In the next picture is the familiar monarch caterpillar (Danaus plexippus) on milkweed. Besides the bright colors that advertise their toxicity, the paired tendrils on each end is a deception so that predators may doesn’t know which end is the head.
On the campus where I used to work (now I teach online), there are cherry trees which always have dozens of large bagworms, which are caterpillars that form a protective bag that is about two inches long. So I brought a few home and put them on our cherry tree for pictures. These odd caterpillars never leave their bag entirely as they move around clumsily along the twigs and leaves of their food plant. You can see some fresh silk in the pictures. They quickly make a security tether in case they need to retreat into their bag, and eventually they will build on this tether to make a stout strap of silk that holds them firmly in place. To move to a different location, they must first chew thru their tether. The species is Thyridopteryx ephemeraeformis, or ‘evergreen bagworm‘, which means they will also feed on conifers. When photographing them, if I sat for a time they would soon emerge and start crawling along a twig. But any disturbance would cause all of them to immediately retreat into their shelters. One wonders how they poop in there.
Bagworms are weird in other ways. They pupate in the bag, and the males emerge as about the plainest, drabbest moths in all of existence. I have never seen one. Adult females don’t emerge from the bag, as they are wingless and legless and rather maggot-like. Males find them through pheromones. After mating, the female lays an egg mass in her bag, and then dies. The pictures in the link above show the strange adults.
Next is a tiny moth. This is Mathildana newmanella. It is a member of the ‘concealer moth’ family, where larvae stay hidden in leaf rolls or in woven bundles of plant debris. Note the ‘Trumpian’ wig.
It’s time to dip into the long queue of Odonate pictures. Here are a pair of amber spreadwing damselflies (Lestes eurinis). I somehow have never noticed these before, even though they become exceedingly common along certain woodland trails. The male shown in the first picture is positively luminous, but the female is also quite lovely. Amber spreadwings develop slightly tinted wings as they mature.
‘Bluet” damselflies are among the most challenging group to identify because there are so dang many species, and many look very much alike. I have a couple of online acquaintances who can identify them in an instant, but I have yet to get the hang of it. In any case, after much lip biting and stress, I suggest that the first bluet damselfly here is a male azure bluet (Enallagma aspersum) [at least I am sure it’s a male], and the second, which is a real eye-popper, looks to be a male northern bluet (Enallagma annexum). Y’all should double click on that one.
Finally, I always check myself for ticks after an outing, and sometimes one or two manage to take a ride home with me. They are almost always American dog ticks, Dermacentor variablis, a tick that accepts a wide range of mammalian hosts. The color pattern informs us that this one is a male. Males take only a brief blood meal. One thing I had learned recently, which makes ticks even weirder, is that they have eyes that are a bit larger than expected. You can see one here as the pale circular spot just above the base of the second leg. Of course, after pictures were taken, this little guy took a ride down the loo.
Tony Eales, a Research Officer from Queensland, writes in with some lovely arthropod photos. His notes are indented.
So it’s winter in the southern hemisphere, and insects and other arthropods are more difficult to find. However when that happens I turn to the leaf litter. I collect a bag of litter from a likely looking spot and then sort through handful by handful on a white bucket lid, looking for movement. The bucket lid helps me see the tiny things crawling around but also has another effect. With a little manipulation of black/white levels on photoshop and some erasing I can isolate the subject in the photo against a white background. This effect can really help bring out the details of these tiny ground-dwelling creatures. Here’s a sample of some of the things that I’ve pulled out of the litter.
Having said all that the first subject is one from the trees rather than the ground. It’s a small male orb-weaving spider Araneus arenaceus the Sandy Orb-weaver. When disturbed, it heads to a twig and hunches up into this shape and becomes basically invisible, looking like any other small protrusion.
Commonly in the rainforest leaf litter I find harvestmen, arachnids in the Order Opiliones. The commonest are these peculiar creatures in the genus Bogania. I can’t find much information about them but I find the huge articulated spiked jaws fascinating. I’d love to observe them catching prey.
The thing about looking at the small stuff is that you’re going to be finding the unstudied stuff fairly regularly. This photo is of a spider in the cobweb spider family Theridiidae. Consulting with the experts on the spiders of my state, we can get it down to the subfamily Hadrotarsinae, but that’s as far as anyone can get. Despite many surveys of the leaf litter in my part of the world, some groups are just not known. I love the long setae on the back.
Next is an insect I’ve shown before. It’s a Trilobite Roach genus Laxta. This one is a nymph although females remain wingless like this but are much darker with thicker exoskeletons.
This is a tiny ant from a genus restricted to the Indo-Australian region. There are only nine described species and they live in small colonies of around 100 ants, foraging in the leaf litter. I think I’ve keyed this one out to Mayriella abstinens, but it’s definitely Mayriella sp. as identified by the deep antennal scrobes (grooves) in the head.
The rainforest leaf litter contains many tiny land snails, most often in the Family Charopidae. There are numerous species with very similar form and thus it is difficult to even get to genus with most that I find. This one, Nautiliropa omicron, however, is quite distinctive with a bi-concave nautiloid shell, delicate ridges and zig-zag patterning.
I’m not sure why this tortoise leaf-beetle was in the leaf litter, as I normally find them in the bushes on live leaves. It’s definitely in the genus Paropsisterna related to P. decolorata, but there’s a problem for researchers describing these beetles, as they have distinctive colours and golden iridescences until they’re dead, and then they lose their colour. It makes it very difficult to compare with the holotypes, many of which were sent to Europe and researchers here aren’t sure if a particular beetle already has a name or not.
Last, some more from my favourite order, spiders. This hairy one is a crab spider. An undescribed member of genus Sidymella. They appear to be fairly common in the leaf litter which is quite unusual for crab spiders. I can’t think of another one that lives on the ground.
Next, I am told by someone more capable in spider ID than I, is genus Spermophora…maybe. It’s a cute little jack-o-lantern-faced cellar spider, Family Pholcidae. I was trying to get to the bottom of what species it is and the key paper on Australian Pholcids has this to say “Spermophora is probably the most chaotic genus within pholcids”, plus it lists only two species in that genus—both far in the tropical north. So who knows. Cute, though.
Last is a jumping spider in the small genus Tara. It’s one of two types I always find in the rainforest leaf litter. Not very colourful for a jumping spider but with those big forward facing eyes they are the most appealing of all spiders.
Of all the posts I’ve written about the amazing things animals do, testifying to the power of natural selection, this is one of the most amazing. It concerns a very tiny animal, Bathochordaeusstygius, a “giant larvacean”, which is a free-swimming marine tunicate, a chordate in the same phylum as we humans. It’s about 1.5 inches (4 cm) long, with a “trunk” where the organs reside, and a tail that helps it swim and, in this case, pumps water to help it eat. The tail contains the notochord (a stiff rod that we have as embryos; it develops into our spinal column), as well as muscles that are crucial in the activity described here.
The larvacean is rarely found “naked,” however, for it builds not one but two houses for itself out of mucopolysaccharides (mucus), a big net-like house about a meter across as well as a smaller, complex house (about 10 cm or 4 inches across) in which the animal resides. And both houses are built and discarded every day!
A new paper in Nature, below, tells how researchers used a new laser apparatus in free-swimming animals off Australia to dissect the structure of the inner house to reveal its workings. That inner house, known for a long time, serves not only to protect the animal (it even has an escape hatch that it uses when discarding the inner house or when something bumps it), but mainly to concentrate small organic food particles, which, after being moved through several chambers by the tail undulations, wind up caught in a net by the trunk, where the animal eats it.
The group largely worked from the Monterey Bay Aquarium in California, which produced this wonderful 4-minute video summarizing the paper’s results:
You can also read a short summary at the New York Times, but it’s not all that great, leaving out really interesting information (don’t worry; I’ll supply it):
You can get the article free by clicking on the screenshot below (you must have the legal Unpaywall app), or find the pdf here. The full reference is at the bottom. And don’t miss the five videos, here, especially the one in which they use dye to track the water flow through the house.
The outer net (“oh”) in the (a) bit below, presumably serves (as does the inner house) to deter predators like fish and jellyfish, but also to catch larger food particles that the larvacean couldn’t eat and would clog the filter. It surrounds the inner house, which is quite complicated and serves mainly as a place to filter organic debris and convey it to the mouth of the larvacean. “si” in the first picture is an abandoned house; after being used for just a day, these sink to the sea floor where they and their food-particle contents are consumed by other animals. There are two channels between the outer “net” house and the inner house, allowing food to be transported neatly to near the larvacean:
The structures of the houses, particularly the inner houses, were determined using a “laser-sheet” apparatus called “DeepPIV”, shown below. This was put in the mid-level depths where the larvae reside and laser scans revealed sections of the houses, which were then assembled by computer to regenerate the three-dimensional structures.
Here’s a photo from the New York Times showing the DeepPIV in action:
And the result of the scanning. The larvacean itself is seen in (a) and (b), with (b) also showing the filters by the head (trunk) where the animal can snack on what’s caught. Water comes in the two inlet channels (e), and then is moved by the flapping of the tail through two other channels that move the food to the filters.
Here’s the flow of water through the house as determined by both the laser scanning and dye-injection experiments that track water flow. It’s hard to see how the water moves (but watch the movies); thewater, after traversing the chambers, winds up flowing through two filters beside the head, where the larvacean takes the food. The filters get clogged up after a day or so, and the larvacean discards both the inner and outer houses and builds the two structures anew. That’s got to take a lot of metabolic energy!
And here is the BIG MYSTERY about this whole thing: how do they build the outer net and, especially, that complex inner house? After all, what we have here is essentially a tadpole without limbs, and yet somehow it’s able to construct two complex structures out of mucus, one inside the other. And I’ve bolded what really knocks me over from the paper’s summary:
The greatest remaining mysteries of larvacean houses concern how they are produced. Whereas a spider builds a complicated web one silky strand at a time, the house of a larvacean is extruded all at once as a rudiment and is then inflated. This leads to the question of how a bank of mucus-producing cells can create such an intricate form within a small, tightly packed bubble. Given their remarkable architecture, it seems almost implausible that these complex marvels should be built to last only a day or two. Future observational tools and vehicles will enable us to observe the construction of giant larvacean houses in their entirety, and to precisely document the frequency with which they are built.
It’s constructed compactly and then inflated! How on earth can this tiny creature do that? Well, we have no idea, so there’s lots of work to be done. What is clear is that the houses, inner and outer, are examples of Dawkinsian “extended phenotypes,” structures that aren’t part of the animal’s body itself but can be conceived of as extensions of the animal (like a termite mound or a beaver dam) The behaviors for making the houses must clearly reside in the larvacean’s genome, as the animal doesn’t learn to do this. What a tangled house we build!
Larvaceans move their tail inside their house to make a current that filters food particles and moves the house through the water. If the filters become clogged or something bumps the house, the larvacean leaves the house through a trap door. The beginnings of a new house lie on the trunk of the animal’s body, and the larvacean inflates the new house and flips inside.
If you don’t find that stunning, you need to buff up your capacity for wonder!
Finally, just to show that this is by no means the largest invertebrate “extended phenotype” in the sea, here’s a video of a giant siphonophore (a class within the phylum Cnidaria, which includes jellyfish, corals, and sea anemones ) estimated to be 150 feet (46 meters) long. How the individual animals (“zooids”) work as a team, and the advantage of such a length, is yet to be determined.
The discovery of the massive gelatinous string siphonophore — a floating colony of tiny individual zooids that clone themselves thousands of times into specialized bodies that string together to work as a team — was just one of the unique finds among some of the deepest fish and marine invertebrates ever recorded for Western Australia. Scientists from the Western Australian Museum, led by Chief Scientist Dr. Nerida Wilson, were joined by researchers from Curtin University, Geoscience Australia and Scripps Institution of Oceanography in exploring the Ningaloo Canyons in the Indian Ocean. Using an underwater robot, ROV SuBastian, they completed 20 dives at depths of up to 4,500 meters over 181 hours of exploration.
This all reminds me of biologist J. B. S. Haldane’s comment about the cosmos: “My own suspicion is that the Universe is not only queerer than we suppose, but queerer than we can suppose.” The “can” says everything about the limitations of our imagination. Nobody could ever have predicted or guessed that a larvacean like this could exist. Nor a frog, nor almost any other organism!