| When alarmed a penaeid will characteristically give a
number of rapid, powerful flexures of the abdomen, driving the prawn
swiftly backwards, often with sufficient force to drive it out of the
water in the shallows. When the abdomen is fully flexed, the sharp
carina on the dorsal abdomen becomes the leading edge, the abdominal
appendages are covered by the tail fan and the thoracic appendages are
folded under the body. The animal thus becomes a hydrodynamically
streamlined body, with the vertical blade of the rostrum and
scaphocerites (part of the antennae) acting as directional fins. Thus a
series of rapid flexures of the abdomen will drive the prawn in a more
or less straight line, usually obliquely upwards from the bottom (Dall
et al., 1990). |
