Decapods are an animal group characterized by having ten legs. Their name, derived from Greek roots, literally translates to “ten feet.” This group includes a diverse range of familiar aquatic creatures such as crabs, lobsters, shrimp, and crayfish.
Understanding Decapods
Decapods are crustaceans belonging to the order Decapoda, which is a large and varied group within the class Malacostraca. Their anatomy features five pairs of thoracic legs.
The first pair of these legs is frequently modified into prominent claws, called chelipeds, which are used for defense, capturing prey, or manipulating food. The remaining four pairs of legs typically serve various functions, including walking, crawling along the seafloor, or swimming. For instance, the American lobster uses its powerful claws for grasping, while its other eight legs enable movement across the ocean floor. Similarly, crabs, shrimp, and crayfish all exhibit this five-paired leg structure.
The Apparent Exception
While decapods are defined by their ten legs, some species may appear to have fewer. For example, porcelain crabs seem to possess only eight legs because their fifth pair is significantly smaller and often tucked away close to their bodies. These reduced legs are not used for walking but are instead specialized for cleaning their gills and body.
Similarly, king crabs also appear to have only six walking legs and two claws. However, like porcelain crabs, king crabs anatomically possess a reduced fifth pair of legs that are typically hidden underneath their carapace and are utilized by females for cleaning eggs or by males for sperm transfer during mating. Despite these visual anomalies, both porcelain crabs and king crabs are true decapods, possessing all ten legs.
Animals with More Than Ten Legs
To distinguish decapods from other multi-legged creatures, it is helpful to note that many animals possess more than ten legs. Centipedes, for instance, are known for their numerous legs, with species having anywhere from 15 to 191 pairs of legs. They are characterized by having one pair of legs per body segment.
Millipedes, on the other hand, have even more legs, typically featuring two pairs per body segment, and some species can have hundreds of legs, with the record holder, Eumillipes persephone, having over 1,300 legs. Beyond these, sea spiders, despite their name, are not true spiders and often have eight legs, though some species can have ten or even twelve legs. These examples highlight the diversity of leg counts in the animal kingdom, clearly differentiating them from the specific ten-legged characteristic of decapods.