Canvas Entomology Introduction

Arthropoda

The largest animal phylum, comprising organisms with segmented bodies, paired jointed appendages, and a chitinous exoskeleton. Arthropods include insects, arachnids, crustaceans, and myriapods.

Jointed Appendages

Paired limbs composed of multiple articulated segments connected at flexible joints, allowing a wide range of motion. This feature enables locomotion, feeding, sensory input, and reproductive behaviors.

Exoskeleton

A nonliving, external skeletal covering secreted by the epidermis. The exoskeleton provides structural support, protection from predators and desiccation, and muscle attachment but must be periodically shed to allow growth.

Chitin

A nitrogen-containing polysaccharide that forms the primary structural component of the arthropod exoskeleton. Chitin often combines with proteins and, in some taxa, calcium carbonate to increase rigidity.

Segmentation (Metamerism)

The division of the body into repeating units (metameres) along the anterior–posterior axis. In arthropods, segmentation facilitates regional specialization and the evolution of complex body plans.

Tagmosis

The process by which individual body segments become fused into functional units called tagmata (e.g., head, thorax, abdomen). Tagmosis allows specialization of body regions for feeding, locomotion, and reproduction.

Bilateral Symmetry

A body plan in which a single sagittal plane divides the organism into left and right mirror-image halves, associated with directional movement and cephalization.

Cephalization

The evolutionary concentration of sensory organs and nervous tissue at the anterior end of the body, forming a distinct head region. This adaptation is pronounced in arthropods and supports active foraging and predation.

Open Circulatory System

A circulatory system in which the circulatory fluid is not confined to blood vessels. Instead, hemolymph circulates through internal body cavities (hemocoel), bathing organs directly.

Hemolymph

The circulatory fluid of arthropods that combines functions of blood and interstitial fluid. It transports nutrients, wastes, hormones, and immune cells, but usually plays a limited role in oxygen transport.

Ecdysis (Molting)

The hormonally regulated process by which an arthropod sheds its exoskeleton to permit growth. Molting involves absorption of the old cuticle and synthesis of a larger new exoskeleton.

Ecdysozoa

A major clade of protostome animals that grow by molting an external cuticle. Arthropods are members of this group, along with nematodes and several lesser-known phyla.

Specialized Appendages

Appendages that are structurally modified for specific functions such as feeding (mandibles), sensory perception (antennae), locomotion (walking legs), or reproduction (gonopods).

Invertebrate

An animal lacking a vertebral column. Arthropods, like all invertebrates, rely on an exoskeleton rather than an internal bony skeleton for structural support.

Adaptive Radiation

The diversification of a lineage into multiple forms occupying different ecological niches. Arthropods exhibit extensive adaptive radiation, contributing to their ecological dominance.

Cuticle

The layered outer covering of the arthropod exoskeleton, consisting of the epicuticle and procuticle. It plays key roles in protection, water retention, and structural integrity.

Arthropod subphylum

Hexapoda (insects), Trilobitomorpha (extinct and now called Artipoda), Chelicerata (Arachnids), Crustacea (shrimp, lobster, crabs), Myriapoda (Centripedes and millipedes)