Anatomy of finfish and shellfish

Unit 12 - Arthropoda

12.2.4. Nervous System
The central nervous system of the American lobster differs little from that of the white shrimp. Lobsters, like shrimps, have a brain, or supraesophageal ganglion, composed of several fused paired ganglia. Running ventrally and posteriorly from the brain are two circumesophageal connectives, a slight swelling on each connective as it passes the esophagus marking the position of the stomatogastric, or connective, ganglia. Behind the esophagus, the connectives are joined by the small tritocerebral commissure.
Due to fusion of the first two thoracic ganglia with three cephalic ganglia to form the subesophageal ganglion, the thoracic portion of the ventral nerve cord in the American lobster contains only five additional ganglia (ganglia of the last two thoracic segments have fused with each other). The abdominal portion of the Ventral nerve cord contains six gan¬glia, one in each segment. This arrangement of thoracic and abdominal ganglia is similar to that in the white shrimp. In spiny lobsters, the thoracic ganglia have undergone greater fusion. Dr. C. J. George and his co-workers at Wilson College, Bombay, India, reported that in the thorax of Panulirus polypizagus there are only two ganglionic masses. The larger, anterior ganglionic mass has resulted apparently from fusion of nine pairs of ganglia (three cephalic, six thoracic), while the smaller, posterior ganglionic mass has come from fusion of two thoracic pairs. Yet in its abdomen, Panulirus polyphagus retains the original number of six ganglia.

As in shrimps, the brain of lobsters receives nerves from sense organs of the head, notably the eyes and antennae. Ganglia of the thorax supply nerves to the mouth parts and thoracic legs. Abdominal ganglia furnish the nerve supply to flexor and extensor muscles of the abdo¬men, to the intestine, and to the abdominal appendages.