Development of spines and sensory setae on the tailfan of the southern rock lobster (Jasus edwardsii Hutton, 1875) (Crustacea: Decapoda)

The pattern of development of setae on the dorsal surface of the telson of juvenile southern rock lobsters (Jasus edwardsii) was followed in individual animals through the first six post-settlement stages by collecting and examining their exuviae by scanning electron and light microscopy. The commonest seta is long and plumose, closely similar in appearance to the hydrodynamic receptors of other crayfish and rock lobsters. These occur only on spines raised above the surrounding surface. The spines are arranged in longitudinal columns. New spines are mostly added posteriorly so that the rostral ones are the oldest and largest, although they can also develop in midcolumn. The rare of addition of setae to spines is constant on all spines within and between animals. These two modes of addition occurring together result in an ordered pattern of setal density grading from anterior to posterior and from the midline laterally. This pattern of setal development differs from those described on the tailfan of crayfish and has not been described previously in any crustacean. Because the number of neurons that innervate setae of this type is constant, the developmental pattern may provide insight into the way in which integumental innervation develops.