About Crustaceans
Crustaceans are arthropods, animals that have an external skeleton (an exoskeleton) jointed appendages to get around on and segmented bodies. Arachnids (spiders) and insects are are also arthropods. Just as insects are ubiquitous on land, crustaceans have successfully populated the waters. Some crustaceans have also adapted to living on land.
-
Examples
-
In the sea, crustaceans include shrimp, krill, crab and lobster. Barnacles, too, are crustaceans. Freshwater examples of crustaceans include water fleas and types of crayfish. Land crustaceans include woodlice and the coconut crab, also known as a robber crab. Crustaceans range in size from the microscopic--like the water flea--to the large crustaceans such as the giant spider crab, with a leg span of up to 4 meters--over 13 feet--and the meter-long coconut crab, which is the largest land crustacean.
Anatomy
-
Crustaceans are invertebrates with appendages that are usually biramous, meaning they have two branches. The digestive tract is a tube that often has a grinder in it, with glands that then absorb the food. Crustaceans have antennae; at some point in their lives, they possess two sets. Within the head near the antennae are kidney-like structures. Ganglia, which serve as crustacean brains, are near the antennae as well. There are ganglia beneath the gut, too. Crustaceans have a head, thorax and abdomen, the thorax being the part that has the appendages serving as legs. The telson is at the end of the crustacean, analogous to a tail.
Life Cycle
-
Most kinds of crustaceans have both male and female members, though some crustaceans are hermaphroditic. Hermaphroditic animals have both male and female reproductive organs. Crustaceans hatch from fertilized eggs. All crustaceans begin as a larval form known as a nauplius, which only has a head and telson. A nauplius only has one eye that later divides into two. The appendages nauplii use to swim later become antennae and mandibles. Once crustaceans have passed from the larval stage, their exoskeletons don't grow with the animal. For a crustacean to get larger, it molts (sheds) its exoskeleton. Crustaceans have different life spans. Some lobsters can live up to 100 years.
Life as a Crustacean
-
There is great variety of lifestyles crustaceans possess. Most crustaceans swim (or walk) freely. Some are parasites. like crustacean lice, and latch themselves onto hosts. An example of a parasitic crustacean is the tongue worm, which lives in the respiratory tract of air-breathing animals. Others crustaceans don't move at all. After reaching adulthood, barnacles live permanently affixed to surfaces like ships. Crustaceans can communicate with one another. Lobsters urinate to communicate. Shrimp communicate by opening and closing their pincers, making underwater noise.
Habitat Ranges
-
The marine crustaceans that we know are those accessible to us and these kinds number in the tens of thousands. Since crustaceans have adapted to so many different kind of habitats, many more species have yet to be discovered in places humans have yet to explore. Some marine crustaceans are part of plankton drift, floating together and providing food to a variety of creatures. Others live on the ocean floor. Though crustaceans primarily live in water, some survive in desert conditions. Some live in forests, under leaves on the forest floor. The coconut crab climbs trees. There have been crustaceans found high in the Andes mountains. Krill live in the cold water of Earth's poles, feeding whales and many other animals, which, in turn, provide food to humans.
-
Related Searches
References
Resources
- Photo Credit Belin Czechowicz
