Life Cycles of Crustaceans

Crustaceans are the arthropods of the sea and include about 30,000 different species. Lobsters, crabs, shrimp, krill and other types of animals are included in the crustacean scientific class. All crustaceans have a chitin and calcium exoskeleton or shell. The life cycle varies greatly among different types of crustaceans, some of which are dioecious and some of which are hermaphrodites. Some crustaceans go through stages of larval development and molting while others hatch as small adults.

Barnacles

Barnacles are a type of crustacean that is hermaphroditic, however, they do not self-fertilize. When mating, a barnacle fertilizes a nearby neighbor's eggs. The adult barnacle broods the eggs under its shell until they reach the nauplius stage. At this time as many as 10,000 larvae swim from the adult's shell as plankton. The larvae go through several molts before reaching the cyprid stage. During this stage, the cyprid attaches to a solid surface, molts and enters the adult stage of its life.

Crabs

While various species of crabs have different life cycles, there are many parts of the life cycle that are similar across different types of these crustaceans. The fertilized female crab produces up to two million larvae that she releases into the ocean. The larvae crab, called zoea, will molt several times before reaching the megalops stage of their development. At this stage, the larvae look like small adult crabs. The megalop will molt several more times before becoming a sexually mature adult. The female crab mates during her last molt, when her shell is soft. The male crab carries her and protects her until her shell again hardens. Her fertilized eggs then develop internally. Once they hatch, the larvae are released into the water.

Lobsters

A female lobster carries her eggs inside her body for nine to 12 months. Depending upon the size of the mother, she may be carrying as many as 100,000 eggs. For an additional nine to 12 months, the eggs are attached to her swimmerets. The eggs hatch and lobsters in their larval stage swim to the ocean's surface. They will molt four times before settling to the ocean bottom. There, they will grow and molt about 25 more times before reaching adulthood. The male lobster will deposit sperm packets on the underside of a female, who will use the packet to fertilize her eggs externally when she lays them.

Shrimp

The life cycle of shrimp vary by species, however, there are similarities across species. The male shrimp attaches a sperm packet to the female. The female animal will release 500,000 to one million eggs into the ocean after fertilization. The eggs will drift for about 24 hours before larval shrimp emerge to feed on algae and small animals. The larvae will grow and molt until reaching adulthood. By adulthood, shrimp are usually five to eight inches in length.

Krill

As with several other types of crustaceans, the life cycle of krill varies among species but has similarities across species. Larval krill hatch from eggs and go through several stages of development -- nauplius, pseudometanauplius, metanauplius, calyptosis and furcilia -- during which they have successive molts. By the furcilia stage, the krill has taken on the shape of an adult. When the krill reaches reproductive maturity, the male krill deposits a sperm sack near the thelycum of the female. In most species, the female krill then releases her fertilized eggs into the ocean where they sink until the larvae hatches and the life cycle begins again.

References

• Barnacle Life Cycle
• Crab Life Cycle
• Lobster Life Cycle and Reproduction