Baby Horseshoe Crabs: these eggs contain tiny horseshoe crab embryos; the hatchlings emerge after 2-4 weeks, but it takes another 10 years for them to mature into adults
Horseshoe crab eggs are initially opaque, with a greenish-gray, blue, or pink appearance, but each egg becomes increasingly translucent as the embryo matures, providing a glimpse of the tiny horseshoe crab developing within.
The legs become visible about five days after fertilization, and the embryo starts moving shortly thereafter, eventually flexing its legs and twirling its body around in the egg. It molts for the very first time after about a week; the embryo will shed its skin three more times as it develops, before it's finally ready to hatch.
The hatchlings usually emerge after 13-33 days. Their bodies are less than 1cm long, and they look just like miniature versions of the adult horseshoe crabs, except that they don't have tails/telsons and their exoskeletons are still soft and translucent. The larvae are sometimes described as "trilobite larvae."
A horseshoe crab can lay more than 80,000 eggs per year, but very few of those eggs actually survive to adulthood. Most of the eggs are eaten or destroyed before they can even hatch, and many of the remaining larvae perish at some point during the 10 years that it takes for them to reach full maturity (i.e. the age at which they begin to reproduce).
Some wild horseshoe crabs can live to be more than 20 years old.
Horseshoe crabs have existed for at least 445 million years, which makes them about 200 million years older than dinosaurs. Their basic physiology has changed very little since then, and modern horseshoe crabs still look strikingly similar to their fossilized ancestors, which is why they're often described as "living fossils."
Despite their common name, horseshoe crabs are not true crabs. In fact, they're not even crustaceans; they belong to a completely different group of arthropods known as chelicerates, which are more closely related to spiders and scorpions than they are to crabs.
Smithsonian National Zoo & Conservation Biology Institute: Horseshoe Crabs
Maryland Department of Natural Resources: Horseshoe Crab Life History
Current Zoology: Developmental Ecology of the American Horseshoe Crab Limulus polyphemus
National Wildlife Federation: Horseshoe Crabs
U.S. Fish & Wildlife: Horseshoe Crab (PDF)
The Horseshoe Crab: Lifecycle
iNaturalist: Atlantic Horseshoe Crab Eggs
blakekathryn
2087
annaxmalina
jacobvanloon
turnnoffyourmind
pixelskylines
