How to track a horseshoe crab

Today I am excited to bring a new video produced by Coastal Kingdom TV, a television series dedicated to sharing the unique and diverse habitats of the South Carolina lowcountry. Host Tony Mills demonstrates the best way to track horseshoe crabs in the tidal flats of South Carolina and does a superb job enlightening us on some of the animal’s unique characteristics.

Why is the blood of horseshoe crabs blue?

Horseshoe crabs use hemocyanin to distribute oxygen throughout their bodies. Hemocyanin is copper-based and gives the animal its distinctive blue blood. We use an iron-based hemoglobin to move oxygen around.

The blood of this living fossil has the ability to  clot in an instance when it detects unfamiliar germs, therefore building up protective barriers to prevent potential infection. This adaptation has made the blood of the horseshoe crab quite desirable to the biochemical industry.

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Atlantic horseshoe crab infographic

Whether we know it or not, the Atlantic horseshoe crab has made a significant impact on many of our lives. The significance of this living fossil can be found in its capacity to resist change for millions of years, its special copper-based blood is crucial to the medical field, and its ability to provide food for millions of migratory birds year after year.

Scientists discover new living fossil. What is a living fossil?

A living fossil is not Russell Johnson (the professor from Gilligan’s Island) or dear Zsa Zsa Gabor (God bless you for holding on!).

I’ll chop it down to say that a living fossil is an organism that more closely resembles a fossil than anything living. For instance, the Atlantic horseshoe crab resembles the fossil record of trilobites more so than anything living. You can also think of living fossils as animals that have gone unchanged after millions of years therefore resembling the fossil record of their ancestors very closely. For instance, alligators and crocodiles haven’t evolved much in the past 230 million years. Horseshoe crabs have gone unchanged in the past 450 million years.

Most recently, a team led by Smithsonian scientists discovered a new living fossil, a primitive eel (Protoanguilla palau), from 10 specimens gathered from a cave in Palau. Palau is an island located in the Pacific 500 miles east of the Philippines and 2,000 miles south of Tokyo. What the scientists noticed was unique to this species (setting it apart from the 800 species of living eels) was the presence of a second upper jaw bone, fewer than the standard 90 vertebrae, and a full set of bony toothed gill rakers. Also, according to the press release from the Smithsonian, “The team’s analyses of total mitochondrial DNA indicate that P. palau represents an ancient, independent lineage with an evolutionary history comparable to that of the entire order of living and fossil eel species.”

It’s as easy as A, B, Sea: H for Horseshoe Crab


Horseshoe crabs are an arthropod more closely related to spiders and scorpions than crabs and lobsters. They have a three part body: prosoma (head), opisthosoma (heavy shell with legs under it) and the telson (tail). This amazing body structure has been unchanged for over 200 million years. Interestingly enough, this is this Beach Chair Scientist’s favorite animal and there have been numerous posts about Limulus polyphemus. Read more here.