Big skates — a species of marine fish — look a little like extraterrestrial creatures.

LONG BEACH — Skate egg casings have been washing in and raising questions among beach users, Tiffany Boothe of the Seaside Aquarium said Sept. 28.

“Some of these casings still have embryos developing inside of them. The problem is if you simply return the egg casing to the ocean it will simply wash back in, however, if you come across one that is still a little wet and feels full you can bring it to the Seaside Aquarium,” Boothe said. “We can put it into a protected saltwater tank where they can continue to incubate. We currently have two egg casings doing just that.”

The incubation period for these egg casings is 11 months. Once hatched, the newborn skates can be released back into the ocean.

About a foot in length and resembling a chunk of seaweed, these egg casings are produced by the female skate and after fertilization are deposited on the ocean floor. A single casing can have anywhere from one to seven embryos inside. Large surf and heavy storms will sometimes dislodge the egg casings from the ocean floor and push them up onto the beach. If stranded on the beach, the casings will dry up and the embryos inside will perish.

The most common skate egg casing to come across on local shores are produced by big skates. Big skates (Raja binoculata) are the largest skates in the world growing 8 feet in length and weighing up to 200 pounds.