The similar sound of “Arthropod” and “Anthropod” often causes confusion regarding biological classification. The accurate biological term for the largest and most diverse animal phylum is Arthropoda, which includes all insects, spiders, and crustaceans. This article clarifies the difference between these two terms by defining the established biological group and explaining the source of the common misnomer.
Defining the Arthropod Phylum
Arthropods are an enormous group of invertebrate animals classified under the phylum Arthropoda, a name derived from the Greek words for “joint” and “foot.” These creatures are characterized by three defining features that separate them from other animal life. The first is the presence of a rigid external skeleton, known as an exoskeleton, which is secreted by the underlying epidermis and composed primarily of a tough material called chitin.
This hard, non-living exoskeleton provides structural support and protective armor. Because this outer shell is inflexible, arthropods must periodically shed the structure through molting to allow for growth. The second defining trait is their segmented body plan, where the body is built from repeating units often fused into distinct regions like a head, thorax, and abdomen.
The third characteristic is the presence of paired, jointed appendages, which gave the phylum its name. These limbs are highly adaptable, serving functions such as sensing the environment, grasping food, or swimming. This combination of a segmented body and flexible, jointed limbs allows for the precise movements that have contributed to the group’s success in nearly every habitat on Earth.
Addressing the “Anthropod” Misconception
The term “Anthropod” is not a recognized or valid classification in biology. Its appearance is almost always the result of a mishearing, misspelling, or phonetic confusion with the correct term, Arthropod. Scientists do not refer to any group of animals as Anthropods.
The most likely source of this confusion is the similarity to the term “Anthropoid,” a legitimate biological classification referring to a suborder of primates. Anthropoids include monkeys, apes, and humans, creatures fundamentally different from arthropods. The term Anthropoid is rooted in Greek, meaning “resembling a human,” which contrasts sharply with the Arthropod’s meaning of “jointed foot.”
Anthropoids are vertebrates, possessing an internal skeleton made of bone, placing them in the class Mammalia. In contrast, Arthropods are invertebrates with a rigid external skeleton. Understanding that “Anthropoid” relates to primates and that “Anthropod” is a non-scientific term resolves the confusion surrounding the accurate biological name, Arthropod.
Major Groups within the Arthropod Phylum
The vast number of species within the phylum Arthropoda are organized into four major subphyla, each distinguished by unique body structures and appendage arrangements. The Chelicerata subphylum includes spiders, scorpions, mites, and ticks. Their defining feature is the absence of antennae; instead, they possess specialized mouthparts called chelicerae and typically have four pairs of walking legs.
Crustaceans, which include crabs, lobsters, and shrimp, are predominantly aquatic and characterized by having two pairs of antennae. Their head and thorax are often fused together into a single structure known as a cephalothorax, and they use gills for respiration. Myriapods, like centipedes and millipedes, are known for their elongated, multi-segmented bodies.
The Hexapoda subphylum is the most diverse group, encompassing all insects, and is identified by its name, which refers to their six legs. Insects typically have bodies divided into three distinct parts: a head, a thorax with three pairs of legs, and an abdomen. These four groups demonstrate the wide range of adaptations that have allowed Arthropods to become the most numerous animal phylum on the planet.