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Posts from the ‘Tunicates’ category

Hurts My Brain – Salp Chain!

These extraordinary animals are not jellyfish. In fact, they are more closely related to you than they are to jellyfish.

These are salps. They are planktonic tunicates with an astounding lifecycle and whose importance includes cycling of nutrients and reducing carbon.

Natasha Dickinson and aggregate form of Salpa aspera. Natasha was my dive buddy on the dives I reference here. We were diving with God’s Pocket in Browning Pass. Photo: Jackie Hildering.

When diving this past April, we happened to be in a bloom of the salp species “Salpa aspera“.

It was truly mind-rupturingly, staggeringly astounding to be carried in the current with so many chains of clones snaking by (they are jet propeled). Yes, I had to make up a new adverb just for this experience!

The stomach is the dark, circular organ you see in each individual in the chain (aggregate).

We also saw an individual break from the chain and move independently! More on that below.

Male Kelp Greenling nipping at Salp aspera. We also saw multiple rockfish species feed on them. Seastar species here is a Striped Sun Star. Photo: Jackie Hildering

Which species of salp?

I did not know which species of salp was all around me. Thankfully, I was able to tap into expertise far greater than my own. Moira Galbraith, Zooplankton Taxonomist with the Institute of Ocean Sciences, very generously shared her knowledge when I sent her my photos, euphoric observations, and request for an ID.

Moira’s answer to my ID request:
“By the size of the stomach and placement (red/green ball), the shape of the ganglion (the c-shape you can see at opposite end from the stomach) and the short projections along where the individuals are attached to each other; I would say that this is Salpa aspera. These have been washing up on beaches off the west coast of Vancouver Island. . ..

Each individual takes in water through the front and channels it out the back. There are muscles bands along the body which create a pulse or pump. Food is taken from the incoming stream and diverted to the stomach. The water going out the back allows the animal to propel itself through the water. Chains work together making it look like a snake or an eel moving through the water.”


Salps can grow and reproduce VERY quickly when conditions are right. They are one of the fastest growing multicellular animal on Earth.

Salps are also big zooplankton.

As a result of their size and number, a whole lot of water gets filtered and the poop that comes out is bigger than the plankton that got consumed. These big “fecal pellets” sink and transport nutrients.

If the fecal pellets make it to the bottom of the ocean, they could carry carbon away from where it will enter the atmosphere. Further, when salps die, their bodies also sink quickly and could thereby remove more carbon from entering the atmosphere.

Source: Nereus Program 


The chains are the “aggregate” form of the salp lifecycle. They are all female clones.

A male individual fertilizes the aggregate.

The females break-off from the aggregate and release a single embryo. The solitary females then go on to develop testes, become males and fertilize the aggregates.

Whoa! Imagine how astoundingly it was for us to watch an individual break from the aggregate and then move independently. If I understand the lifecycle properly, this would have been a female with an embryo.

Salp lifecycle. – alternation of generations where the asexually reproducing form makes the sexually reproducing form. Source: Henschke et al.
Salpa aspera aggregate and the individual in the video (on the bottom left). All the pink animals on the ocean bottom are Great Winged Sea Slugs and their egg masses!

More information:

Madin et al., 2006:
“Development of such large populations is presumably made possible by the high rate and efficiency of filter feeding by salps, their rapid growth and their alternation of sexual and asexual reproduction. These characteristics permit a rapid population response by salps to favorable food availability, such as may result from seasonally high phytoplankton productivity in oceanic regions of water mass intrusions and mixing along fronts. In some locations, high population densities of salps can be produced in as little as a few weeks.”

Woods Hole Oceaonographic Institute:
“From their clear, blob-like appearance, you’d be forgiven for mistaking the salp for a jellyfish. But it turns out that these gelatinous zooplankton actually are more closely related to humans than to brainless jellyfish. Unlike the jellyfish, salps (and humans) boast complex nervous, circulatory and digestive systems, complete with a brain, heart, and intestines.

Salps use jet propulsion to efficiently glide through the ocean. They’re great at multitasking: while expanding and contracting their muscles to move, they’re also pumping phytoplankton-rich water through their feeding filters, taking in the nutrients they need to survive . . . .

When food is plentiful, they can quickly create more chains, and each salp can increase rapidly in size. This superpower makes them one of the fastest-growing multicellular animals on Earth. Like all good things, the salp bloom comes to an end when all their available food is consumed.

Found throughout the world ocean, salps play an essential role in the ocean’s biological pump. Because they feed on phytoplankton—which grow in the presence of sunlight and carbon dioxide—salp poop is extremely rich in carbon. When these fecal pellets (and dead salps) fall to the seafloor or are snapped up by other twilight zone creatures, it’s like putting carbon into a bank vault.

The carbon remains at the bottom of the ocean for years, if not centuries, helping regulate our climate. Scientists don’t yet have an accurate assessment of how changes in salp numbers and distribution could affect the ocean’s carbon cycle—and impact climate change—but it’s clear that these critters play an important role.”

New York Times article about the research of Sutherland and Welhs (2017).

[Note that this research was on two different species of salp.]

“Meet the salp. It typically lives in deep waters, where its barrel-shaped body glides around the ocean by jet propulsion, sucking in water from a siphon on one end and spitting it back though another. It swims alone for part of its life. But it spends the rest of it with other salps, linked together in chains arranged as wheels, lines or other architectural designs . . .

Over years of watching them swim in chains, she [Dr. Sutherland] made a surprising discovery. They synchronize their strokes when threatened by predators or strong waves and currents. But while linked together in day-to-day life, each salp in the chain swims at its own asynchronous and uncoordinated pace. Counterintuitively, this helps salps that form linear chains make long nightly journeys more efficiently.

The life story of the sea salp is peculiar. Each one starts life as a female, then switches to male . . .

Making chains is part of their life cycle, and if these chains break, they don’t link back together. Each salp lives only a few days or a month in two stages: solitary, and in a colonial chain. A solitary salp gives rise to a colony of genetically identical salps asexually. The salps are connected in a chain that starts as a coil around the solitary salp’s gut. It grows over time and eventually breaks free, the beginning of the colony phase. Each individual within the chain will reproduce sexually. Through spawning, a male’s sperm reaches a female’s egg, forming a baby solitary salp that eventually swims out of its parent. “That solitary will make a chain and so on,” said Dr. Sutherland. It’s a chicken-or-the-egg kind of situation.

Perhaps to enhance a salp’s reproductive success, many salps migrate vertically, from the deep sea toward its top at night and back down during the day. At the surface, they can congregate with a greater chance that the sperm of one hits an egg of the same species.

And salps in linear chains are particularly skilled at this migration, traveling thousands of feet each night, at speeds around 10 body-lengths a second. “That’s like running a marathon every day,” said Dr. Sutherland.

You might think that fast synchronized, coordinated swimming strokes would be the way to make that happen. But each salp in the chain pumps to the rhythm of its own built-in pacemaker.

The resulting swim isn’t as fast, but it’s smooth and sustainable, with less interference from the wakes made by individuals. It’s like the difference between a Porsche and a Prius, said Dr. Sutherland. A Porsche can accelerate quickly to top speeds, but a Prius is more fuel-efficient.”

Poorly lit photo but gives you a sense of how long the aggregate / chain can be. I would estimate this one to be nearly 4 metres long. ©Jackie Hildering

Henschke N, Everett JD, Richardson AJ, Suthers IM. Rethinking the Role of Salps in the Ocean. Trends Ecol Evol. 2016 Sep;31(9):720-733. doi: 10.1016/j.tree.2016.06.007. Epub 2016 Jul 18. PMID: 27444105.

L.P. Madin, P. Kremer, P.H. Wiebe, J.E. Purcell, E.H. Horgan, D.A. Nemazie (2006), Periodic swarms of the salp Salpa aspera in the Slope Water off the NE United States: Biovolume, vertical migration, grazing, and vertical flux, Deep Sea Research Part I: Oceanographic Research Papers 53 (5), 804-819

Nereus Program Our jelly-like relatives: Common misconceptions about salps

New York Times (2017) – It’s Better to Swim Alone, Yet Together, if You’re a Salp

Sutherland Kelly R. and Weihs Daniel (2017) Hydrodynamic advantages of swimming by salp chains. R. Soc. Interface.142017029820170298

Wood’s Hole Oceanographic Institute – CREATURE FEATURE – Salp

Salpa aspera aggregate and another dive buddy, Linnea Flostrand. ©Jackie Hildering.

Tunicates – Your Distant Cousins?

Here’s one of your highly evolved and wonderfully unique marine neighbours.

Five colonies of Mushroom Tunicate. I believe this is Distaplia occidentalis.

Mushroom Tunicates are one of the many species of tunicate in the NE Pacific Ocean. The tunicates, as simple-looking as they may seem to you, are our closest invertebrate relative. That’s how complex their anatomy is.

From Dr. Laura Cole quoted from the Smithsonian blog Tunicates — Not So Spineless InvertebratesAbout 3,000 tunicate species are found in salt water habitats throughout the world. Although tunicates are invertebrates (animals without backbones) found in the subphylum Tunicata (sometimes called Urochordata), they are part of the Phylum Chordata, which also includes animals with backbones, like us. That makes us distant cousins . . .  What unites these diverse groups and makes them our relatives? All animals in the Phylum Chordata have a notochord, a flexible backbone like structure, at some point in their lives.”

So here are some fascinating facts that may influence how we perceive organisms that look very different than we do. 

Tunicates have a unique exoskeleton called a tunic.

Photo showing the diversity of colour in Mushroom Tunicates.

Some tunicate species are solitary, living as distinct individuals. Others, like Mushroom Tunicates are COMPOUND tunicates where individuals live together in the colony, within one tunic. The individuals in the colony are called zooids. The zooids have specialized functions that can serve the collective colony. In this species each individual has its own incurrent siphon and pharynx (throat-like structure) to bring in water to filter feed. The individuals in the colony share digestive, reproductive and circulatory organs and excurrent siphons (to carry water out).

Oh, and by the way, tunicates are the only animals known to have a heart that can pump in two directions; they can reverse the direction of circulation.

Photo shows how compound tunicate colonies share a stalk. 

Tunicates are hermaphrodites where reproduction occurs both by cross-fertilization and self-fertilization. The fertilized eggs are brooded inside the colony in a brood pouch and the timing of when parents hatch out the relatively large tadpole-like larvae has been found to be influenced by light (morning appears to be preferred).  

Some species of tunicate have been found to have bacteria associated with them that provide chemicals that ward off predators and disease-causing microorganisms. You can imagine the human interest in how these chemicals might help our species fight off pathogens. 

And in case this all isn’t wild enough, colonial species of tunicate are known to regenerate their entire body from a group of cells named blood cells. This too makes them of great interest to we humans, who are tunicates’ distant relatives, but evolved to NOT be able to regenerate body parts.

Further information from Dr. Laura Cole, from her much-valued resource  “Tunicates — Not So Spineless Invertebrates”

The most common tunicates are sometimes called sea squirts because when touched or alarmed by a sudden movement, their muscles contract and the water in the animal shoots out. They are sessile after their larval stage, meaning that they remain attached to a hard substrate, such as dead coral, boat docks, rocks or mollusk shells, all of their adult lives. The name “tunicate” comes from their outer covering, called the tunic, that protects the animal from predators, like sea stars, snails and fish. Unlike the sessile sea squirts, other kinds of tunicates float in the water their entire lives. The salps and pyrosomes are mostly transparent tunicates that look a bit like jellyfish floating freely—some pyrosomes have be known to reach 60 feet (18 m) in length. Much smaller but still visible to the naked eye are the larvaceans—tiny tadpole like creatures that live inside a small house that they build and regularly replace.

[Note there are two related The Marine Detective blogs: (1) “Pyrosomes! Say What?” at this link and (2) “Otherworldly Drifter. Mind Blown” at this link.]

What unites these diverse groups and makes them our relatives? All animals in the Phylum Chordata have a notochord, a flexible backbone like structure, at some point in their lives.

Sea squirts have a notochord only in the larval stage which they use to swim and find an ideal place to attach—one that is bathed in particle-rich waters, since like all tunicates they are filter feeders and rely on water currents for food and nutrients. Once a good location is found, the larva attaches with a suction-like structure and metamorphosis begins. The notochord shrinks and gets absorbed into the body as the animal changes into an adult, and the tunic forms as the transformation occurs. The animal will then spend its days feeding on tiny particles from the water, primarily bacteria. 

There are two types of sea squirts: solitary and colonial. The solitary animals live separately all of their lives inside of their tunics. Each has two siphons—the oral siphon that receives the nutrient rich current and the atrial siphon that excretes the waste. Colonial species share a common tunic and sometimes also share the atrial siphon. Colonies of sea squirts are formed as a result of budding—when the larva settles and changes into the adult form, it then splits (or buds) to produce new individuals, called zooids. Colonies can be a few centimeters to several yards wide depending on food availability and predation.  

Sea squirts don’t look much like us as adults on the outside, but they have a digestive system similar to ours—with an esophagus, stomach, intestines and a rectum. But there are plenty of other differences. Unique to the benthic tunicates is a heart that reverses its beat periodically. It’s still a mystery to researchers why the tunicate heart will circulate blood through the heart in one direction and then switch to the opposite direction, or if the ability gives them some sort of advantage. 

On land, we don’t encounter sea squirts that often, although they are increasingly eaten by some Mediterranean, Asian and South American countries. Not only is the soft body inside of the tunic eaten, but the tunic itself can be pickled and enjoyed later. Compounds from several tunicate species could be useful in medical treatments for diseases ranging from cancer to asthma. Tunicates act as ocean purifiers, since they consume bacteria, and they can send a message that heavy metals are present in ecosystems where they are found, since they absorb metals like zinc and vanadium. Because they like to attach to hard surfaces, sea squirts are often found on the underside of boats, or inside motors, where they can wreak havoc on equipment, and some have become invasive species after being transported from their native ranges. Their relatives the pyrosomes, also called sea pickles, sometimes wash up in large numbers on the shore and are known for their bioluminescence

Like with many a large family, most of us don’t know about these distant relatives found in the ocean, but that doesn’t mean they aren’t worth keeping an eye on.”

Photos of other species of tunicate living in the NE Pacific Ocean.
Note that there are many more species than what I show here.

Solitary tunicate species: Pacific Sea Peach, Halocynthia aurantium, to 15 cm tall. Species like this have led to tunicates sometimes being referenced as “Sea Squirts” due to to larger, solitary species of tunicate having the “tendency to squirt seawater periodically from the main branchial siphon to back-flush sediments, other indigestible matter, and small animals from the filtering basket (about 10 times per hour in some species). Source: Snail’s Odyssey.
Another Pacific Sea Peach.
Solitary tunicate species: Glassy Tunicate, Ascidia paratropa to 15 cm tall. 
Solitary tunicate species: Sea Vase. In this photo, multiple individuals are “reaching” out of a crack in a wooden piling.
Ciona savignyi to 15 cm tall.
Solitary tunicate species: These Transparent Tunicate have a problem. This species gets invaded by a wicked parasite (as opposed to all those gentle and meek parasites out there) . . . the Spotted Flatworm! This species of flatworm curls up, sneaks in through the tunicate’s branchial siphon, unrolls, eats the tunicate’s internal organs over 3 to 7 days and then moves on, leaving behind the empty tunic. They are species specific parasites, apparently specializing in invading Transparent Tunicates. The dark coil you see here is the waste inside their rectums. Transparent Tunicate = Corella willmeriana to 7.5 cm tall. Spotted Flatworm = Eurylepta leoparda to 2.5 m.
Alabaster Nudibranch atop Orange Social Tunicates (Metandrocarpa taylori.
Light-Bulb Tunicate. Clavelina huntsmani to 5 cm tall.

Stalked compound tunicate – possibly Distaplia smithi

Compound tunicate species: Red Ascidian. Aplidium solidum to 20 cm across.

Compound tunicate species: Lobed Compound Tunicate. Cystodytes lobatus, irregular size and shape, can be more than 50 cm wide.

Compound tunicate species: Lobed Compound Tunicate. Cystodytes lobatus with a feeding Orange Sea Cucumber.

Compound tunicate species: Lobed Tunicates and Mushroom Tunicates (and a whole lot more) 🙂

Compound tunicate species: May be Pale Mushroom Compound Tunicate. Aplidiopsis pannosum to 5 cm wide. 


Invasive Tunicates

This is an example of an invasive tunicate species now found off the coast of British Columbia (and many other places). .
It’s the Lined Compound Ascidian, Botrylloides violaceus. All the other species shown here are not invasive

Preoccupied with Parasites

Preoccupied with parasites!

That’s not usually a good conversation starter is it?

But, read on. It’s worth it! If you are fascinated by adaptations and the interconnectedness of species . . . even when it involves parasites.

These are Transparent Tunicates (aka Transparent Sea Squirts). They are not parasites. They are highly evolved animals with a primitive backbone. They take in food particles through one siphon in their strong “tunic” and expel waste through the other siphon. See the siphons?


The dark you see here is the waste inside their rectums. Yep, they are filter feeders and clearly take in some sand too. What’s this then about parasites?

This species gets invaded by a wicked parasite (as opposed to all those gentle and meek parasites out there) . . . the Spotted Flatworm! This species of flatworm curls up, sneaks in through the tunicate’s branchial siphon, unrolls, eats the tunicate’s internal organs over 3 to 7 days and then moves on, leaving behind the empty tunic.

They are species specific parasites, apparently specializing in invading Transparent Tunicates. The following photos clearly show you the Spotted Flatworm presence there and the tunicates are now mere shells of their former selves.

All the internal organs are gone in the heavily invested individual in the photo below.


In having the privilege of learning even from individual animals by diving the same areas frequently. I recently saw the progression for individual Transparent Tunicates and the Spotted Flatworms that had invested them. The following photo is from March 1st, 2020. I’ve now added arrows to show the parasites.

The following two photos show you reality  24 days later. The originally invested Transparent Tunicates are dead and the Spotted Flatworms have moved into their neighbours.

Below is another perspective on the same individuals.


I truly hope that in these times where our own species is facing extreme challenges, that this information still creates awe, connection and respect for the lives of others. Maybe it’s more important than ever.

Wishing you health, resilience, and strength of community.

Transparent Tunicate = Corella willmeriana to 7.5 cm.
Spotted Flatworm = Eurylepta leoparda to 2.5 m.

Pyrosomes! Say What?

Late  2017 to 2018 – Getting reports of pyrosomes again:
– December 10 – Central Coast of BC (Borrowman Bay on the north west side of Aristazabel island) by Stan Hutchings & Karen Hansen – small and scattered.
– November 27 – Oregon (
Netarts Bay and Oceanside Beach) by Todd Cliff
– January 1 – Tofino (Wickaninnish Beach) by Christie McMillan

Pyrosomes – literally “fire bodies” in Greek – are weird and wonderful marine organisms that have been sighted in large numbers from Oregon to British Columbia’s central coast to Yakutat Alaska! The inspiration for their name is that, when alive, they can generate “brilliant, sustained bioluminescence” (Bowlby et al).

A beach full of Pyrosomes ©Marie Fournier.

January 24, 2017: A beach scattered with Pyrosoma atlanticum. Stunning photo by ©Marie Fournier. Location: West Beach on Calvert Island; 51°39’13”N; 128°08’27″W. 

Specifically, it is Pyrosoma atlanticum that is being seen in large numbers and about which I have been getting inquiries dating back to February of last year. More about this species later. First some general information about this genus.

As gelatinous as pyrosomes appear, they are not closely related to jellyfish. They are colonial pelagic tunicates often found in dense aggregations. Tunicates are highly evolved. They even have a primitive backbone (a notochord).

February 19, 2016 (the first  inquiry I got about this species): A single Pyrosoma atlanticum colony found and photographed by ©Tiare Boyes while diving at ~70′. It was being snacked on by hermit crabs and marine snails. Location: Just outside God’s Pocket; 50°50’15”N, 127°33’40”W.

Pyrosomes on salmon trolling gear.
©Dobie Lyons.

Colonial? Yes, each pyrosome is made up of thousands of individual “zooids” that are connected by tissue (a tunic) to form a rigid, bumpy, hollow tube that is open at one end. This design allows the individuals to filter feed. Cilia draw water into each zooid where plankton are removed with mucous filters; the filtered water passes into the tube; and then out the back end of the colony. This current not only allows feeding but also propulsion of the colony.

But wait, it gets even more remarkable. The individuals making up the colony are clones. Thereby, the colony can regenerate injured and broken parts. “Unless all individual clones are killed at the same time, a colony can theoretically live forever, shrinking and growing based on available food and physical disturbance.  Individual clones are hermaphroditic; they make both eggs and sperm (Oceana).” It is hypothesized that when colonies meet, they may also reproduce sexually.

One Star Trek inspired biologist has referenced pyrosomes as the “the Borgs of the sea”. I just have to share that description with you:

 “One long pyrosome is actually a collection of thousands of clones, with each individual capable of copying itself and adding to the colony. And like members of the Borg, which are  mentally connected, pyrosome members are physically connected– actually sharing tissues. And while the Borg live in a big scary ship, pyrosomes are the big scary ship. The whole colony is shaped like a giant thimble with a point on one end and an opening on the other . . . . Each little “wire basket” is the stomach of one member of the colony. They take water in through a mouth on the outside of their space-ship body, pass it through the little basket to filter out the nom bits, and squirt water out the other end, into the big hollow space in the middle” (R.R. Helm; Deep Sea News).

“Big scary ship”? The “Giant Pyrosome” (Pyrosoma spinosum) can indeed be up to 18 m long with an opening reported to be up to 2 m wide. But that is a species found in tropical waters.

The pyrosome species being sighted along the west coast is much smaller. Pyrosoma atlanticum (class Thaliacea) can reach lengths of 60 cm but as you can see from some of the images here, those being reported nearer to shore are much smaller, ranging from about 5 to 8 cm long. This species may be colourless, pink, grey, or bluish-green.

It is the most widespread pyrosome species. It is found in all oceans with the generally accepted range being between temperate latitudes of 50°S to 50°N.

October 1, 2016: Pyrosoma atlanticum were also being seen but much further offshore. Photo: ©Christie McMIllan. Location: About 145 km off the west coast of Vancouver Island.

Thereby, up to around mid Vancouver Island, British Columbia is part of their range but they are usually much further offshore. It is only when wind and tides wash them onto beaches that more of us get to see them. The species already generated a lot of interest much further to the south when they were getting blown ashore in Oregon from October to December 2016. They were also being sighted far off BC’s coast in October.

It was already unusual to see them off BC’s coast beyond 52°N in March. In May 2017, they were being reported off Yakutat, Alaska, beyond 59°N. This is extremely unusual and is indicative that there must be a warm water mass carrying them further north.

December 2016 photo from ©Stan Hutchings and Karen Hansen. Location: Quigley Creek in Laredo Channel; 52°39’15”N, 128°44’05”W

For those lucky enough to see them at night, pyrosomes bioluminesce with an intense, bright, blue-green light that can apparently last more than 10 seconds. Their bright lights inspired biologist T.H. Huxley to write in his1849 journal: “I have just watched the moon set in all her glory, and looked at those lesser moons, the beautiful Pyrosoma, shining like white hot cylinders in the water.”

Pyrosoma are unique not only in how brilliant and sustained this bioluminescence is, but also because they are among the few marine organisms where light is made in response to light, not only in response to touch. Thereby, a wave of light passes from one individual in the colony to the next AND from colony to colony (Bowlby et al)! The light is believed to actually be made by bacteria living within the zooids.

Oh to see that!

Thank you to those who relayed all the queries and sightings. This is a solid case of how the observations, interest and knowledge of many allow a bigger picture to come together. This picture may have relevance to science and certainly has value in generating greater interest in our lesser known, wonderfully weird, light-emitting, totally tubular, marine neighbours.

A Pyrosoma atlanticum colony. ©Stan Hutchings and Karen Hansen.


TEDx talk on Pyrosomes – June 7, 2018


Particularly large Pyrosoma atlanticum, 35 nautical miles off Neah Bay, Washington. In photo: Dobie Lyons. Photo by Alan Tyler.




Video by Patrick Anders Webber. 

Video below if from New Zealand.

Otherworldly Drifter. Mind Blown.

Today was the first time ever that, while diving, I made a gesture to my dive buddy indicating that my brain had exploded.

We weren’t deep; the remarkable find that had me awestruck was at 3 to 5 metre depth. It’s a known species and is found throughout the Atlantic, Pacific and Indian Oceans but  . . . . it’s certainly extremely rare here around NE Vancouver Island and it is SO otherworldly.

Let me take you on a short journey of discovery.

I was already pretty excited when I found the organism in the photo below. I knew it to be a salp “aggregate” and was delighted that there was an amphipod hitchhiker. See it?

Cyclosalpa bakeri with amphipod hitchhiker ©Jackie Hildering;

Cyclosalpa bakeri with amphipod hitchhiker.
©Jackie Hildering;

Salps are such unique gelatinous animals! They belong to the group of highly evolved invertebrates known as tunicates. Most tunicate species live attached to the bottom when they are adults but salps remain Ocean drifters for their whole lives. Because of their gelatinous “tunic” they have even been referred to as Ocean Gummy Bears.

Their reproduction is totally otherworldly! They alternate between two forms. The image above is of the “aggregate” form or “salp chain” that, dependent on species, can be made up of millions of individuals. The aggregate form reproduces sexually to form a barrel-shaped solitary form. The solitary form buds off (asexually) to produce the individuals that make up the aggregate form and so on! Salps apparently grow faster than any other multicellular organism! (Source: JelliesZone).

Back to the dive  . . . so I was already pretty thrilled to have seen the salp chain of this unique species and THEN I saw something hovering above me, zeppelin like.

Brain exploded. WHAT was this?!

Pelagic tunicate. Salp species - Thetys, solitary phase. To 33 cm. ©2015 Jackie Hildering

It was about 25 cm long.

It had openings on both ends.

It clearly had internal organs.

And it had unique projections on what I assumed was its back end.

The look on my dive buddy Natasha Dickinson’s face in the image below says it all!

Dive buddy with Thetys. ©2015 Jackie Hildering

Dive buddy Natasha Dickinson with Thetys salp. ©2015 Jackie Hildering

I was pretty sure that it was the solitary form of some species of salp but  . . . so big?

Pelagic tunicate. Salp species - Thetys, solitary phase. To 33 cm. ©2015 Jackie Hildering

Good view of gut. ©2015 Jackie Hildering

As soon as I got home I grabbed my copy of Wrobel and Mills’ “Pelagic Coast Pelagic Invertebrates” and emailed a few photos of this unique find to Andy Lamb, co-author of Marine Life of the Pacific Northwest.

Ahh – it’s wonderful to have friends in deep places. Andy came back very quickly with the ID. It was a salp indeed, in fact, the world’s biggest. Thetys* in the solitary form can grow to 33 cm! The common name is the Twin-sailed Salp.

From Dave Wrobel’s The JelliesZone webpage: “Thetys is truly an impressive member of the zooplankton.  It is the largest species of salp along the West Coast and is relatively easy to distinguish from all others.  Unlike most gelatinous animals, the body is relatively firm due to the thick spiny test (the test, or tunic, is the hard outer covering typical of many tunicates, hence the name for the group).  It retains its shape even when removed from the water.  Solitary individuals have 20 partial muscle bands . . . that are used for constricting the body while pumping water for feeding and locomotion.  A pair of pigmented posterior projections are very distinctive, as is the darkly colored, compact gut . . . Like other salps, Thetys continuous pumps water through a mucous net to extract phytoplankton and other small particles.   Although relatively uncommon in Monterey Bay [and therefore very uncommon so much further north where I sighted this individual], this widespread species can be found in temperate and tropical waters of the Pacific, Atlantic and Indian Oceans, to depths of about 150 meters.”

Pelagic tunicate. Salp species - Thetys, solitary phase. To 33 cm. ©2015 Jackie Hildering

©2015 Jackie Hildering

I was intrigued how an animal that lives in the open Ocean and depends on plankton could be so big?

How could it filter enough plankton out of the water?

Pelagic tunicate. Salp species - Thetys, solitary phase. To 33 cm. ©2015 Jackie Hildering

©2015 Jackie Hildering

I came upon research from MIT (2010) that revealed how salps could get enough nutrients to be so big and fast growing.  Their mucus nets are astounding in how they are able to trap incredibly small-sized plankton. With this find, the researchers referenced salps as “the vacuum cleaners of the ocean” and confirmed how important they are because of what they do to huge volumes of climate-changing carbon.

In the Oceanus Magazine article Salps Catch the Ocean’s Tiniest Organisms, the researchers explain “As they eat, they [the salps] consume a very broad range of carbon-containing particles and efficiently pack the carbon into large, dense fecal pellets that sink rapidly to the ocean depths, Madin said. “This removes carbon from the surface waters,” Sutherland said, “and brings it to a depth where you won’t see it again for years to centuries.” And more carbon sinking to the bottom reduces the amount and concentration of carbon in the upper ocean, letting more carbon dioxide enter the ocean from the atmosphere, explained Stocker” [thereby reducing the amount in the atmosphere where it impacts climate.]

I of course also hoped to find a good photo or video of the salp chain of this species (the aggregate form) and came upon this 1-minute clip by Patrick Anders Webster (taken off the coast of central California).

Wow!!! Mind-blown again.

And below, an additional video from Patrick from May 2016, also off the coast of California.

[*You may have noticed that the full scientific name for this tunicate species is Thetys vagina as assigned by the German naturalist Wilhelm Gottlieb Tilesius von Tilenau in 1802. Likely at that time, “vagina” did not yet have its anatomical meaning and the species name was chosen for the Latin origin of the word meaning “wrapper” / “sheath”.]

Further information:

Scripps zooplankton guide –

Jelly Zone –