Cardioacceleratory reflexes triggered by mechanoproprioceptors of the swimmerets in the stomatopod crustacean Squilla oratoria

The heart of Squilla oratoria is innervated by processes arising from the cardiac ganglion, which lies on the outer surface of the heart wall. The ganglion is regulated by one pair of cardioinhibitory nerves and two pairs of cardioacceleratory nerves. Cardiac acceleration accompanied activation of the five pairs of swimmerets in the first to the fifth abdominal segments. The cardioacceleratory nerves were activated when swimmerets beat strongly. Activation of the cardioacceleratory nerves was caused by electrical stimuli to a nerve branch extending to the swimmerets from the first nerve root of the abdominal ganglion. Bursts of afferent impulses were recorded from the nerve branch of the first nerve root corresponding to periods of protractive and retractive swimmeret movements. Afferent impulses were recorded from the nerve branch when the articular membrane was artificially boosted up. Cardiac acceleration during active swimmeret movements in Squilla is attributable to a reflexive response triggered by the movements. Putative mechanoproprioceptors on the articular membrane between the sterna and basipodite in the swimmerets may be responsible for the cardioacceleratory reflex.