--- title: "Circulatory System of Sponges: How Water Does the Job" url: https://thesea.org/sponge-circulatory-system/ date: 2026-11-13 modified: 2026-11-13 lang: en author: "Blane Perun" description: "Do sponges have a circulatory system? No heart, no blood, no vessels. Instead, choanocytes pump seawater through a canal system that delivers food and oxygen and removes waste, helped by ocean currents. How the sponge water-canal system works." categories: - "Sponge Q&A" word_count: 1823 --- # Circulatory System of Sponges: How Water Does the Job [TheSea.Org](/)▸[Sponges](/sponges/)▸[Sea Sponge Facts](/sea-sponge-facts/)▸Sponge circulation # Do Sponges Have a Circulatory System? — How Seawater Does the Job of Blood Sponges ▸ Q&A By [Blane Perun](/about-blane-perun/) November 13, 2026 10 min read Do sponges have a circulatory system? No. Sponges have **no heart, no blood and no blood vessels**. Instead, they use an **aquiferous (water-canal) system**: collar cells called **choanocytes** beat their flagella to pull seawater in through pores, push it through a network of canals and chambers, and expel it through openings called **oscula**. That flowing water delivers food and oxygen to the sponge’s cells and carries away carbon dioxide and waste, doing the job a circulatory system does in other animals. Wandering cells then move nutrients within the body. Quick facts Heart or bloodNone Transport systemAquiferous (water-canal) system PumpChoanocyte flagella Gas exchangeDiffusion across cell surfaces Internal transportArchaeocytes carry nutrients Help from currentsAmbient flow can draw water through passively Every animal has the same basic needs: get food and oxygen to its cells and get rid of carbon dioxide and waste. Most animals do that with a circulatory system, a pump and a set of tubes carrying blood or a similar fluid around the body. Sponges solved the problem differently. They bring the ocean itself through their bodies. Seawater flows through a maze of channels that reach close to every cell, so the sea does the work that blood does in us. Water movement has been central to every reef system I’ve built. Pumps, wave makers and sumps exist to keep water moving past every animal in the tank, delivering food and oxygen and carrying waste to the filtration. A sponge is that whole life-support system packed into one animal, and understanding it explains almost everything else about how sponges live. The aquiferous system The aquiferous system, from the Latin for “water-carrying”, is the network of pores, canals and chambers that water flows through in a sponge. Water enters through many small pores called ostia on the sponge’s surface. It travels through incurrent canals to the choanocytes, either lining a central cavity in the simplest sponges or packed into small chambers in more complex ones. From there it flows through excurrent canals to one or more large openings, the oscula, and leaves the sponge. The system is one-way, in through the small pores and out through the large ones, so the sponge does not re-breathe its own exhaled water. Our [sponge diagram](/sponge-diagram/) labels each part, and our guide to [sponge body types](/asconoid-syconoid-leuconoid-sponges/) shows how the canal system becomes more elaborate in larger sponges. The pump: choanocytes Instead of a heart, sponges have thousands to millions of tiny pumps: the flagella of their collar cells. Each choanocyte has a single whip-like flagellum surrounded by a collar of microvilli. The flagella beat continuously, and because they are arranged in chambers with their tips pointing toward the exit, their combined action creates a steady current through the sponge. The same cells catch bacteria and fine particles on their collars as the water passes, so pumping and feeding are done together. In the more complex sponges, the many small chambers slow the water down as it passes the collars, giving them time to filter it, and then the narrowing excurrent canals speed it up again so it leaves the oscula as a jet strong enough to carry waste well away. The overall volume is remarkable: large sponges can move very large amounts of water each day; see [how much water sponges filter](/sponges-can-filter-an-amount-of-water-100000-times-their-size-each-day/). Breathing without lungs or gills Sponges exchange oxygen and carbon dioxide by simple diffusion across the surfaces of their cells. Because water flows past cells lining the canals and chambers, and because no cell is far from that flowing water, oxygen can diffuse in and carbon dioxide out without any special breathing organ. The same applies to nitrogen waste, mainly ammonia, which diffuses into the outgoing water and is carried out through the oscula. This works because a sponge’s cells are spread through a thin or highly perforated body, never packed into a thick mass far from water. It is the same principle that limits the size of animals without circulatory systems in general: every cell needs to be close to the source of oxygen. Moving nutrients inside the body Some cells in a sponge are not in direct contact with the water channels. For them, mobile cells act as a delivery service. Food particles caught by choanocytes are taken into the cell and partly digested, then passed to **archaeocytes** (amoebocytes), mobile cells that crawl through the jelly-like mesohyl between the sponge’s outer skin and its canals. Archaeocytes finish digesting the food and carry nutrients to other cells, collect and remove waste, and can even turn into other cell types as needed. In this sense, archaeocytes play a role somewhat like blood cells, though they move by crawling rather than being carried in a fluid. Our page [are sponges multicellular?](/are-sponges-multicellular/) describes these cells in more detail, and [what do sea sponges eat?](/what-does-sea-sponge-eat/) covers their diet. | Job | In humans | In sponges | | --- | --------- | ---------- | | Pump | Heart | Choanocyte flagella | | Transport fluid | Blood | Seawater flowing through canals | | Vessels | Arteries, veins, capillaries | Incurrent and excurrent canals | | Gas exchange | Lungs | Diffusion across cell surfaces | | Food delivery to cells | Blood plasma | Archaeocytes crawling through mesohyl | | Waste removal | Kidneys, lungs | Diffusion into outgoing water | Free help from the current Sponges do not always have to pump all the water themselves. The ocean’s currents can help. In the 1970s the biologist Steven Vogel showed that water flowing over a sponge can draw water through it passively. Because the oscula are often raised above the surrounding surface, or sit at the top of tubes and chimneys, water moving across them is faster than water near the base, creating a slight pressure difference that pulls water out of the oscula and draws it in through the pores lower down. The same principle draws air through a prairie dog burrow or up a chimney. This “induced flow” means sponges in currents get extra flow at no energy cost, which may be one reason large sponges thrive in places with steady currents, such as the walls of Cozumel, where the plankton-rich current helps barrel and tube sponges grow especially large. Other animals without a circulatory system Sponges are not the only animals that manage without a heart and blood, but they use a unique solution. Cnidarians, such as jellyfish, sea anemones and corals, have no circulatory system either. Instead they have a gastrovascular cavity, a single gut-like space with one opening, which both digests food and distributes it through the body; in corals, canals connect the polyps of a colony so nutrients can be shared. Flatworms have a branched gut that reaches close to every part of their thin bodies, and they absorb oxygen through their skin. Comb jellies use a system of canals that branch from the gut. In every case, the trick is the same: keep every cell close to a source of food and oxygen. Sponges are unusual because the fluid they use is the ocean itself, drawn in from outside rather than held in an internal cavity, and because the flow passes through the body in one direction rather than in and out of the same opening. This is part of why sponges are so efficient at filtering. A coral or anemone must wait for food to drift into its tentacles. A sponge actively pulls water through itself all day long. The reef’s living filter Because their whole body is a water pump, sponges have a large effect on the water around them. On coral reefs, sponge communities filter enormous volumes of water, removing bacteria and fine particles and taking up dissolved organic matter released by corals and algae. Studies on Caribbean reefs suggest that the sponge populations on a reef can filter a volume of water equivalent to the water column above the reef in a matter of days or less, depending on sponge density and currents. By turning dissolved organic matter into cells that other animals can eat, sponges recycle nutrients that would otherwise be lost, an idea known as the sponge loop. In a reef aquarium, a mature population of small sponges on live rock contributes to water quality in a similar way, quietly working alongside the skimmer and filters, which is one reason experienced reef keepers tend to welcome them rather than remove them. Stopping the flow Sponges can also slow or stop their pumping when conditions are bad. When the water becomes cloudy with sediment, or when a sponge is disturbed, many species narrow their oscula and pores, slow their flagella or contract their canals, reducing flow to avoid clogging. Some freshwater sponges have been filmed making slow, whole-body contractions that flush sediment out, a behaviour researchers have compared to a sneeze. Glass sponges can stop pumping within seconds when disturbed, using electrical signals that spread through their syncytial tissue, something remarkable for an animal without nerves. These responses show that the sponge’s water system is not just a passive set of pipes but a controlled system, adjusted to conditions from moment to moment, much as a reef keeper adjusts pumps and flow when conditions in a tank change. For more on how sponges sense and respond without a nervous system, see [does a sea sponge have a brain?](/does-a-sea-sponge-have-a-brain/) Frequently asked questions Do sponges have a circulatory system? No. They have no heart, blood or vessels. Water pumped through their canal system does the job instead. How do sponges get oxygen? Oxygen diffuses into their cells from the seawater flowing through their canals and chambers. What pumps water through a sponge? The beating flagella of choanocytes, or collar cells, helped in some cases by ambient currents. What is the aquiferous system? The network of pores, canals, chambers and oscula through which water flows in a sponge. How do sponges get rid of waste? Waste such as ammonia and carbon dioxide diffuses into the outgoing water and leaves through the oscula. Do sponges have blood cells? No, but archaeocytes crawl through the body carrying nutrients and removing waste, a somewhat similar role. Sources & further reading - Vogel, S. (1977). Current-induced flow through living sponges in nature. *PNAS* 74: 2069–2071. - Leys, S. P. et al. (2011). The sponge pump: the role of current induced flow in the design of the sponge body plan. *PLoS ONE* 6(12): e27787. - Leys, S. P., Mackie, G. O. & Meech, R. W. (1999). Impulse conduction in a sponge. *Journal of Experimental Biology* 202: 1139–1150. - Brusca, R. C., Moore, W. & Shuster, S. M. (2016). *Invertebrates*, 3rd ed. Sinauer Associates. Continue reading More from Sponges [Sponge Q&ADoes a Sponge Have a Brain?How sponges sense without nerves. ](/does-a-sea-sponge-have-a-brain/) [Sponge Q&AWhat Sponges EatHow sponges filter their food. ](/what-does-sea-sponge-eat/) [Sponge Q&ASea Sponge FactsClassification, size, habitat, diet and lifespan. ](/sea-sponge-facts/) BP Last updated November 13, 2026 Written by Blane Perun Blane Perun has been exploring Earth’s oceans and marine life for over 25 years. Founder of TheSea.Org in 1999, underwater photographer, coral aquaculture pioneer, and explorer of 80+ countries. [About Blane Perun →](/about-blane-perun/) [More on Sponges →](/sponges/)