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A cohort of  juvenile Atlantic horseshoe crabs (Limulus polyphemus) are spending the winter at MBL under the watchful eye of Veterinarian Lisa Abbo as part of a collaboration with Charles River Laboratories.

"They were collected this past June and are being raised through the winter to be released back into the wild in the spring," said Abbo. "This gives them a head start by getting them past the most vulnerable life stages."

С�����Ƶ 700 juvenile horseshoe crabs were collected this spring. This is the MBL's first year collaborating with Charles River Laboratories on this project, which also includes Mystic Aquarium and Rutgers University.

This video shows one the larger horseshoe crabs in the group. It molted for the third time over Thanksgiving weekend and now measures 9 mm across.

We call them crabs, but Limulus polyphemus are more closely related to spiders and scorpions than true crabs. The blood of Limulus polyphemus is used in biomedical research to test pharmaceuticals and medical devices for potentially deadly endotoxins. This test, called the Limulus Amebocyte Lysate (LAL) takes advantage of the horseshoe crab’s primitive immune system, which causes its blood to clot when it encounters potentially harmful gram-negative bacteria.

Feature photo: Left: Dozens of the juvenile horseshoe crabs spending the winter at the MBL. | Right: One of the larger horseshoe crabs in the group. It recently molted and now measures 9mm across. Credit: Lisa Abbo.