Crabs inhabit nearly every corner of the planet, from the deepest oceans to tropical forests, showcasing an extraordinary range of adaptations. These crustaceans thrive in diverse environments, varying greatly in salinity, temperature, and terrain. Their widespread presence underscores their ecological importance across aquatic and terrestrial ecosystems. The variety among crab species, in terms of size, appearance, and behavior, is remarkable.
The Global Count of Crab Species
The current estimate for the number of known true crab species, belonging to the infraorder Brachyura, hovers around 7,000 to 7,600. This figure is not static, as ongoing scientific discovery and reclassification efforts continuously refine it. This number highlights the biodiversity within this group of crustaceans, and the count primarily encompasses what are known as “true crabs.”
Defining What Makes a Crab
True crabs are classified under the infraorder Brachyura, a term that translates to “short-tailed” in Greek, reflecting a key characteristic. They possess a hard outer shell, or exoskeleton, which provides protection and structural support. They have ten legs, with the foremost pair often modified into specialized pincers called chelae. Their short, flattened abdomen is tucked underneath the main body or thorax, distinguishing them from other crustaceans with more prominent tails. This compact body plan, along with eyes often mounted on stalks, allows for efficient movement and foraging in diverse habitats.
Factors Influencing the Species Count
The number of recognized crab species is dynamic, influenced by continuous scientific exploration and taxonomic revisions. New species are regularly discovered, particularly in underexplored environments like the deep sea or remote freshwater systems. Advancements in genetic analysis also contribute to changes in species counts by providing new insights into evolutionary relationships. This can lead to the splitting of what was once considered a single species into multiple distinct ones, or conversely, the lumping of previously separate species. Our understanding of crab biodiversity is always evolving, making the total count a fluid estimate.
Broad Categories of Crabs
Crabs exhibit adaptability, inhabiting diverse environments that lead to broad ecological categories. Marine crabs, the vast majority, reside in all the world’s oceans, from coastal waters to hydrothermal vents. Freshwater crabs, numbering over 800 species, thrive in rivers, lakes, and estuaries, showcasing adaptations to less saline conditions. Land crabs, while often needing access to water for reproduction or gill moisture, have developed structures allowing them to spend significant time on terrestrial surfaces, even in tropical forests. True crabs (Brachyura) are distinct from other “crab-like” crustaceans, such as hermit crabs and king crabs, which belong to a different infraorder called Anomura, and these Anomurans are not included in the species count for true crabs.