Accessory circulatory organ

Definition

A pulsatile auxiliary structure in arthropods that augments hemolymph circulation independently of the dorsal vessel (heart-aorta system). These organs typically operate as localized pumps at extremities or within appendages where the main circulatory flow is inadequate, maintaining perfusion to antennae, legs, wings, or other distal tissues.

Etymology

From Latin accessorius (additional, supplementary) + circulatorius (circular, cyclical) + organum (instrument, tool)

Example

In the American cockroach (Periplaneta americana), the antennae contain an accessory circulatory organ at their base that pulses autonomously to drive hemolymph through the long, narrow flagellum; in spiders, leg hearts (ampullary hearts) act as segmental accessory organs that contract in coordination with the opisthosomal heart to maintain pressure in the extremities during locomotion.

Synonyms

• accessory heart
• ampullary heart
• leg heart
• pulsatile organ

Related Terms

• dorsal vessel
• Hemolymph
• ostium
• aorta
• Pericardial sinus
• hemocoel
• cardiac valve
• antennal heart
• wing heart

Usage Notes

The term distinguishes these structures from the primary dorsal vessel and from non-pulsatile auxiliary channels (such as lateral vessels or head sinuses). Usage varies: 'accessory heart' often implies a discrete, chambered pump, while 'pulsatile organ' emphasizes function over structure. In some contexts, 'ampullary heart' specifically refers to the segmental leg hearts of arachnids and certain crustaceans. Not all arthropod groups possess these organs; they are best developed in active, large-bodied insects and arachnids with elongated appendages.