ESPINOZA, S.Y.**; BREEN, A.; VARGHESE, N.; FAULKES, Z.; Univ. of Texas- Pan American: Loss of escape-related neurons in spiny lobster (Panulirus argus)

Lobsters and crayfish are two of many decapod crustaceans that use escape tailflips when under attack. The neural circuitry responsible for escape behavior has been well studied in crayfish. This circuitry includes lateral giant interneurons (LG), medial giant (MG) interneurons, and fast flexor motor giant neurons (MoGs). Many decapod crustaceans have lost some or all of the escape circuit, however. Slipper lobsters (Palinura: Scyllaridae) have lost their entire escape circuit. It was previously hypothesized that slipper lobsters lost their escape circuit because of their adoption of digging as an anti-predator strategy. Spiny lobsters (Palinura: Palinuridae) are scyllarids� closest relative, but their general morphology more closely resembles crayfish then scyllarids. Because spiny lobsters are not diggers, the prediction is they should have giant interneurons. Spiny lobsters (Panulirus argus) can perform tailflip escape behavior using non-giant tailflipping. The ventral nerve cord of P. argus was removed and examined. As a positive control, all techniques were also performed on crayfish Procambarus clarkii. In crayfish, the MG and LG axons are clearly visible under a dissecting microscope, and in nerve cord sections. The MoGs are visible in backfills, with their distinctive anatomy making them readily distinguishable from other fast flexor neurons. The same techniques showed no evidence of giant neurons in P. argus. Ventral nerve cord sections showed no large axon profiles in the dorsal region of the nerve cord. Backfills showed the fast flexor motor neuron pool contained one less neuron than in crayfish, and the remaining fast flexor neurons show none of the characteristic anatomical features of the MoG.