Do Lobsters Have Blood? (Explained)

Marine animals adapted to their environment in very different ways. Some of them use blood for circulation, but others, such as sea stars, can use seawater instead. Have you wondered if lobsters have blood and what their circulatory system looks like? In this blog post, we’ll talk all about that but let’s begin with a quick answer:

Lobsters have blood that circulates from their heart to seven different arteries. The color of lobsters’ blood is transparent, but when it comes into contact with oxygen, it turns light blue.

However, this certainly doesn’t tell the whole story. Below I’ll explain more about lobsters’ blood and why its color is blue. Furthermore, I’ll explain whether lobsters can bleed or not, how their blood circulates through the body, and what their artery system looks like. Next, I’ll explain why lobsters’ circulatory system is called “open”. Read on!

Lobsters’ blood

Lobsters have blood which is part of their circulatory system. However, their blood color may be surprising to some of you. Lobsters’ blood turns blue when exposed to oxygen, but when inside the body, it’s actually colorless.

Why is lobsters’ blood blue?

Lobsters have blue blood because of the presence of the copper-containing blood pigment called hemocyanin. This pigment appears light blue in oxygenated conditions. In contrast, vertebrates and many other animals, including humans, have iron-rich blood pigments called hemoglobin that make our blood red.

Interestingly, not only lobsters’ blood color is fascinating but also their skin color. Lobsters’ pigment makes their skin multiple colors, such as blue, orange, yellow, and even white. You can read more about it in my other blog post: “Why Are Lobsters Different Colors?“.

Do lobsters bleed?

So, what happens if the lobster is injured? Can you see its blue blood? According to professor Joe Kunkle, lobsters’ blood clots very quickly, so simple injuries don’t cause significant problems. Surprisingly, when the lobster is out of the water, the blood clots even more effectively.

Another interesting fact is that the time for blood to clot depends on the harshness of the injury and the body part. For instance, the damage to the lobster’s carapace may be dangerous because clotting can interfere with the heart. However, the injury to the underside of the animal’s body can cause clotting interfering with its nervous system.

But, can you see the blue blood of the lobster? Well, when the lobster that bleeds is found at a reasonable depth, its blood will be transparent. The reason for that is that the oxygen level at those depths is relatively low, and as I mentioned above, hemocyanin is colorless without oxygen.

If lobster were brought from a store’s tank or floating crate, its blood would be blue because the oxygen level in the tank and ocean surface water is high. In this case, the hemocyanin would turn blue because of the high oxygen level.

Do lobsters have a heart?

Lobsters have their heart located above the stomach on the upper surface of the animal. However, instead of a four-chambered heart like we do, they have a single-chambered sac that consists of muscles and several openings called ostia.

How does blood circulate in lobsters?

Blood Flow in the Open Circulatory System of Lobster
Blood Flow in the Open Circulatory System of Lobster by Macmillanhighered

The circulatory system of lobsters is known as an “open” system, and it consists of three parts:

  • a muscular heart,
  • thin-walled arteries, carrying the blood away from the heart and branching eventually into smaller vessels,
  • a series of irregular channels or sinuses that conduct the blood back to the heart through the gills.

During the circulation, the blood enters the first part of the lobster’s circulatory system – the heart – which is a single-chambered tube of striped tissue. In adult species, the heart makes up 0.1 – 0.15% of the total body weight.

The heart is innervated from the ventral nerve cord by the cardiac ganglion, which consists of nine neurons, four control cells, and five motor neurons. The beating of the heart is accomplished by impulses provided by control cells, which excite the motor cells. The resulting impulses cause the heart to contract rhythmically.

Interestingly, the heart of an adult lobster can beat at a rate of 50-136 beats per minute. Next, blood exits the heart through arteries – five anterior and two posteriors. The arteries branch to supply all the organs of the animal with blood, such as muscles, appendages, intestine, legs, mouthparts, and more.

After the blood passes through the tissues, it collects in the sinuses and goes to the sternal sinus in the thorax. Next, it flows to the sinuses in the gills and returns to the pericardial cavity. Next, it enters the heart again through three pairs of valved slits, called ostia. The volume of lobster’s blood may differ, but it averages about 20% of the animal’s wet weight.

The artery system of lobsters

lobster artery system
Lobster’s Artery System by Animal Physiology, 2004

Lobsters have an extensive and highly branched arterial system to deliver blood to all tissues. They have seven arteries that leave the heart and provide different organs with blood: 

  • The median artery that supplies blood to the brain and antennae,
  • The paired anterior lateral arteries that supply the antennae, eyestalks, portion of the hepatopancreas – soft, green substance in the body cavity, and the lateral branchiostegal walls,
  • The paired hepatic arteries that supply the hepatopancreas as well,
  • The sternal artery that gives branches to the gut, hepatopancreas, and gonads. Next, it bifurcates at the floor of the thorax and forms anterior and posteroventral branches. The first branch supplies the first three pairs of pereiopods, the thoracic nerve cord, the mouthparts, and portions of the antennal glands. The second one supplies the last two pairs of pereiopods, the abdominal ventral nerve cord, and a small part of the ventral abdominal musculature. 
  • The dorsal abdominal artery supplies the abdominal musculature and swimmerets. It bifurcates into two arteries that supply the tail fan of the lobster. 

Why do lobsters have an “open” circulatory system?

The difference between closed and open circulatory systems is quite simple. The closed circulatory system occurs when blood stays within blood vessels. Humans are the perfect example because our heart pumps blood into the vessels to reach the tissues and organs.

In contrast, the open circulatory system occurs when blood, rather than being closed tight in arteries and veins, travels flows freely through and may be directly open to the environment. This circulatory system is common to all arthropods, including lobsters.

Lobsters have a simple system of arteries but don’t have veins that return the blood to the heart. Instead, blood returns to the heart through interconnecting spaces called venous sinuses. Because of that, the lobsters’ circulatory system is defined as “open”.


  • Wilkens, J. L., et al. “Evolutionary Derivation of the American Lobster Cardiovascular System: An Hypothesis Based on Morphological and Physiological Evidence.” Invertebrate Biology, vol. 116, no. 1, 1997, pp. 30–38. JSTOR, Accessed 13 Aug. 2022.
  • J. Cobb, Bruce Phillips “The Biology and Management of Lobsters.” Academic Press, 1980.

You may also like:


Welcome to Bubbly Diver!
I’m glad to see you here. This blog is created for all marine creature lovers by a bubbly diver - me, Dori :)