Cardiac nervous system in the ostracod crustacean Vargula hilgendorfii

Abstract

We examined morphologically innervation of the heart of the ostracod crustacean Vargula hilgendorfii. The heart is single chambered and composed of a single layer of myocardial cells characterized by localization of myofibrils at the epicardial side. A nerve net in the heart was determined by vital staining with methylene blue. Electron microscopy revealed that a single neuron situated on the outer surface of the dorsal heart wall sends an axon into the heart wall. The axon of the dorsal neuron is branched widely and forms many neuromuscular junctions on the myocardial cells. A pair of extrinsic nerves, each of which contains several axons, enters the heart bilaterally and forms numerous nerve terminals on the dorsal neuron and myocardial cells, while no synaptic structures were found in the nerve terminals. The results suggest that the heart of V. hilgendorfii is neurogenic, with a single cardiac neuron having both pacemaker and motor functions.