Aripinnad

Aripinnad are fins that are not paired with the left and right sides of the body. In fishes this typically refers to the dorsal fin or fins and the anal fin, as well as the adipose fin in some lineages. In contrast, paired fins, such as the pectoral and pelvic fins, attach on both sides of the body.

Anatomy and development: Unpaired fins are supported by fin rays (lepidotrichia) and a skeletal framework that can be cartilaginous or bony. They develop from embryonic fin folds and become segmented as the animal grows. Some unpaired fins may have spines at their leading edges, while others are soft throughout.

Function: Unpaired fins contribute to propulsion, stabilization, and steering during swimming. The dorsal and anal fins help prevent rolling and aid in maneuvering, braking, and maintaining directional control. The adipose fin, present in some species, is smaller and its exact function is debated, though it is often rich in sensory structures and may influence water flow around the body.

Variation and evolution: The number, size, and arrangement of aripinnad vary widely among fishes. Most ray-finned fishes (Actinopterygii) have one or more dorsal fins and a single anal fin; many also possess an adipose fin. In other groups, such as certain cartilaginous fishes, dorsal fins are prominent while anal fins may be reduced or absent. The evolution of unpaired fins is linked to changes in locomotion, stability, and ecological niche.

Taxonomic note: The presence and configuration of aripinnad are commonly used in comparative anatomy and taxonomy to differentiate taxa and understand functional adaptations in aquatic locomotion.