Yes, crustaceans are animals. They belong to the animal kingdom, specifically classified as a subphylum of the phylum Arthropoda. This places them alongside insects, spiders, and myriapods as invertebrates with segmented bodies and exoskeletons.
Defining the Animal Kingdom
Animals are multicellular organisms, with bodies composed of many cells organized into specialized tissues. These tissues, such as nerve and muscle, enable complex functions and coordinated movements. Animals are heterotrophic, obtaining nutrition by consuming other organisms. This process of ingesting organic matter provides the energy for their growth and development, distinguishing them from plants.
Most animals exhibit motility at some stage of their life cycle, allowing them to move independently within their environment to find food or mates. Most animal species reproduce sexually, involving the fusion of male and female gametes. This reproductive strategy leads to offspring that develop with a fixed body plan.
Characteristics of Crustaceans
Crustaceans are invertebrates with a rigid external skeleton, known as an exoskeleton, primarily composed of chitin and calcium carbonate. This hard covering provides both protection and structural support against predators and environmental stresses. To accommodate growth, crustaceans periodically shed this exoskeleton through molting, leaving them temporarily vulnerable until a new, larger one hardens.
Their bodies are segmented, commonly divided into a cephalothorax (fused head and thorax) and an abdomen. Each segment can bear jointed appendages, specialized for activities like walking, swimming, defense, or sensing the environment.
Crustaceans have two pairs of antennae for touch and chemical sensing, and specialized mouthparts, including mandibles and maxillae, for efficient food processing. Most crustaceans thrive in aquatic environments, predominantly found in oceans and freshwater bodies worldwide, though some species have adapted to terrestrial life. Many species also undergo a distinctive developmental stage known as a nauplius larva.
Common Crustacean Examples
Crustaceans include many familiar creatures.
Crabs have broad, hard shells and prominent claws, often moving sideways across beaches and seabeds. Lobsters have elongated bodies, large, often asymmetrical claws, and are found on ocean floors, prized as food.
Shrimp are slender-bodied, known for swimming with long antennae and flexible tails, inhabiting diverse aquatic environments. Barnacles are sessile adults, attaching to surfaces like rocks or boat hulls and filter-feeding with feathery appendages.
Krill are small, planktonic crustaceans vital to marine ecosystems, resembling tiny shrimp and forming large swarms that feed whales and other large marine animals. These examples illustrate the range of forms, habitats, and ecological contributions within the crustacean group, all sharing animal biological criteria.