(Describer) Under a round logo of a wave, title: Ocean Today.

(Describer) With their dome-like shells, horseshoe crabs lie in wet sand.

(male narrator) Ancestors of horseshoe crabs date back 450 million years.

(woman) The horseshoe crab is called the "dinosaur of the ocean"

(Describer) Maggie Pletta:

because it's been around since before the dinosaurs. The dinosaurs went extinct, this guy stayed around.

(narrator) Horseshoe crabs are arthropods. That means they have an exoskeleton, a segmented body and jointed appendages, but no backbone. Horseshoe crabs molt, leaving their old shells behind and growing new, larger, shells. Their main eyes are compound, like a housefly's, with five more eyes on top of their shells and two underneath. They have eyes here, along their shell, and down their tail. They can tell moonlight, sunlight. They have sensors-- they know the temperature of the water, the dissolved oxygen-- all of that, just from their body.

(narrator) The coolest thing about horseshoe crabs is their blood. It's blue and copper-based, and it's really useful. When this crab is injured, gets a cut on its body, bacteria can get into it from the water. Horseshoe crab blood "Jell-Os" around that bacteria and stops it from getting into the body.

(narrator) Because of special properties, scientists can use horseshoe crab blood to sniff out harmful bacteria that might be in medicines for humans.

(Pletta) There's a compound called limulus amebocyte lysate, otherwise known as LAL. They use the LAL to test every vaccine, needle, medical equipment-- anything that goes into your body is tested with LAL.

(Describer) A woman puts something in a test tube.

(narrator) While scientists are working on synthetic alternatives to horseshoe crab blood, every time you get a shot, thank a horseshoe crab.

(Describer) Titles: OceanToday.noaa.gov. Accessibility provided by the US Department of Education.

Accessibility provided by the U.S. Department of Education.