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Decapod Crabs

Reproduction and Development

Decapod crabs are built like a folded-up lobster. The abdomen, which is equivalent to a tail, is folded up tightly underneath its body to form an abdominal flap.

Photo of undersurface of male crab showing abdominal flapWhen you turn a crab over and look underneath, you can tell a crab's sex by looking at its abdominal flap. A male crab has a small triangular flap, while a female crab has a broad oval-shaped abdominal flap.

When a male and female crab mate, many female decapod crabs can store the male sperm until her eggs are ready to be released. When the eggs are released, the stored sperm flows over them and they become fertilised.

Photo of female crab in berryThe female crab holds the fertilised eggs in a big spongy mass between its abdominal flap and the body. The eggs are cemented to the pleopods, which are small legs, creating the "berried" appearance.

To keep the eggs healthy, the female crab continually "waves" water over the eggs with the pleopods.

Graphic of crab zoea

When the eggs hatch into zoea larvae, they drift away in the ocean currents as plankton. As the juvenile crab grows in size, it goes through a series of moults, each larval stage changing form and function as it grows in a process called metamorphosis.

At each moult more segments are added to the end (posterior), and the feathered limbs are replaced by the clawed limbs. The megalops stage more closely resembles the adult decapod crab.

Graphic of crab megalops


Tubercled Crab
Reef Crab
Smooth-handed Crab
Variegated Shore Crab
Red Bait Crab
Sowrie Crab
Mudflat Sentinal Crab
Smooth Shore Crab
Seaweed-decorator Crab
Crab reproduction
Crab parasitism

Home Page
Rocky Shores
Tidal Levels
Intertidal Zonation
Environmental Factors
Biological Factors
Feeding Relationships



photo of Keith DaveyLife on Australian Seashores
by Keith Davey (C) 2000

Learning Consultant - Media
The University of Newcastle

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Scientific Consultant: Phil Colman
site created 01.01.98 : updated 01.04.2000