This female sharpnose crab, Scyra acutifrons, at left was releasing her young into the water in our Life on the Edge exhibit. Here her abdomen is completely open, revealing masses of thousands of pale brown larvae (see yellow arrows) being held in place by her pleopods (see blue stars), special appendages used just for this. The blue arrow indicates one of the larvae swimming towards the surface.
Most of the time, a female will hold her abdomen folded closely against her underside. It’s only when “in berry” (with eggs) that she will open it to reveal her clutch. As development progresses for several weeks to months, she will periodically open this abdominal flap to aerate the eggs and pick out non-viable eggs.
Like many familiar crabs, sharpnose crabs have internal fertilization, but the females may store the sperm for months or longer before using it to fertilize thousands of eggs. Sharpnose females may reproduce several times a year, not just in the spring.
When her eggs are ripe, the female will allow the sperm to flow over them as they are being released from her body. She will immediately attach these fertilized eggs to the underside of her abdomen, the area between the abdominal wall and the abdominal “tail.” When her eggs are hatching, she will either flick her abdominal flap into the water to release the young, or as in this case, use her front claws to assist their release into the water column.
As with most newly-hatched young, these larvae immediately began swimming to the surface. In the wild, they would become part of the plankton.
Newly hatched young look nothing like their parents and go through several molts to transform into the basic shape, shown at left, a more adult-like form that will settle out of the plankton to the substrate below.
The spines often seen on crab larvae found in our plankton tows are thought to help the larvae stay buoyant in the water column. The “tail” is used to scoop up tiny zoo-plankton prey towards the mouth. Other appendages are used for swimming.
Come visit the Aquarium and learn more about our animals in the Life on the Edge exhibit!