The life cycle of a crab involves physical transformations that make finding a single name for a “baby crab” challenging. Crabs begin as tiny, free-swimming organisms that bear little resemblance to the familiar adults. The journey from egg to adult is a series of distinct stages, each with its own scientific name, appearance, and way of life. This life history allows them to disperse widely before settling into their adult habitat.
The Scientific Names for Baby Crabs
The first larval form to hatch from the egg mass is known as the Zoea (plural: Zoeae). This creature is microscopic, often less than a millimeter in size, and is entirely planktonic, drifting with the ocean currents. The Zoea looks nothing like a crab, appearing more like a small shrimp or other crustacean larva, often characterized by long spines for protection.
The Zoea stage involves a series of molts, typically ranging from four to eight sub-stages, lasting around 30 to 45 days. After the final zoeal molt, the larva transforms into the second stage, called the Megalopa. While still considered a larva, the Megalopa begins to show rudimentary crab-like features, such as claws and walking legs. Its abdomen, or “tail,” remains extended, unlike the tucked-under abdomen of an adult crab. The Megalopa is the transitional form between the Zoea and the miniature adult.
The Transition to Juvenile Crab
The Megalopa stage marks a shift from a purely drifting existence to finding a suitable place to live. As it grows, the Megalopa uses environmental cues like changes in salinity and light to guide its movement toward coastal or estuarine settlement areas. The final major metamorphosis occurs when the Megalopa settles onto the seafloor and undergoes its last larval molt to become the first Juvenile crab. This stage closely resembles a miniature adult, with the characteristic broad, flattened body and the abdomen tucked beneath the carapace. The juvenile will continue to molt and grow until it reaches sexual maturity.
Early Life Habitat and Diet
The Zoea is a free-swimming organism in the water column, relying on the ocean currents for dispersal. During this planktonic phase, the larvae are filter feeders, consuming microscopic organisms like phytoplankton. They must feed exogenously, meaning they require food from the environment, though some species may have enough yolk to sustain the initial stages.
The Megalopa, though still able to swim, becomes more active in selecting a place to settle, often moving toward estuaries or nearshore environments. Once the Megalopa molts into the Juvenile, the crab adopts a fully benthic, or bottom-dwelling, existence. These juveniles seek protective habitats, such as seagrass beds, rock crevices, or muddy substrates, which offer refuge from predators. Their diet shifts to include detritus, worms, and other tiny invertebrates, marking a change from filter-feeding to actively scavenging and hunting.