The horseshoe crab, Limulus polyphemus, is actually more related to spiders, ticks and scorpions than crabs. It has been an experimental system for over a century, and has been intensively studied because of the remarkable properties of its circulation system. For example, its blood does not contain hemoglobin. Instead, it contains a copper-containing protein called hemocyanin that causes the blood to appear colorless when it lacks oxygen and dark blue in the presence of oxygen. A compound isolated from its blood is also used to determine if intravenous drugs are contaminated by bacteria. The compound induces clotting in the presence of bacterial endotoxin.
The species is among the oldest in the world – estimated to be at least 300 million years old. It seems to have retained many ancestral characteristics in terms of morphology and development over long periods of time; indeed it is often considered a “living fossil.”
Limulus is a good model for studying the evolution of development. Fertilized embryos can be stored at 4 degrees C, which halts their development, but these can be restarted again anytime within the next 12 months simply by warming them up. Limulus’ embryos are amenable to standard procedures for examining the patterns of gene expression, and while the eggs are not transparent, the embryos develop on the surface of the yolk and can be readily imaged throughout development.
This species is commonly found along the Atlantic coast of North America. They live on the bottom of sandy beaches with shallow water and are most active at night, when they dig through sediment for food such as worms and algae. While not raised from generation-to-generation in the lab, the species is easily found all along the east coast of the US, and within its breeding season, mass quantities of eggs are commercially available.
In the Eastern US there are threats to the species due to over-harvesting of their eggs for use as eel bait. This in turn is affecting the Red Knot bird population, which feed on the crab’s eggs.
|Species Name||Data Type|
|Limulus polyphemus||NCBI BioProject ID Link|