SEROTONIN IMMUNOREACTIVITY IN THE VENTRAL NERVE CORD OF THE PRIMITIVECRUSTACEAN ANASPIDES TASMANIAE CLOSELY RESEMBLES THAT OF CRAYFISH

Syncarid crustaceans, of which only a few living species remain, have articulated segments with well-developed appendages along the length o f the body, an arrangement thought to resemble that of the earliest ma lacostracan crustaceans. Decapod malacostracans have fused thoracic se gments and reduced abdominal appendages. Modern representatives of the two groups are separated by at least 300 million years of evolutionar y history. The serotonin immunoreactivity of ganglia and connectives f rom the ventral nerve cord of the syncarid Anaspides tasmaniae was com pared with that of serially homologous ganglia of the crayfish Cherax destructor. Both species show the serotonin-immunoreactive longitudina l fibre bundles described from other decapods and thought to be part o f a neuromodulatory network., They also have in common a number of the cell bodies associated with this system. Each species has some seroto nergic cells in the region examined that are not present, or that do n ot stain, in the other species.