Snapping behaviour in intraspecific agonistic encounters in the snapping shrimp (Alpheus heterochaelis)

During intraspecific agonistic encounters in snapping shrimp (Alpheus heterochaelis) the behaviour of the snapper, emitting a fast water jet by very rapid closure of the large modified snapper claw, and the receiver was analysed by single frame video analysis before, during, and after the snap. During snapping the opponents usually face each other. Snapping is most frequently preceded by touch of frontal appendages. The snapping animal keeps its snapper claw slightly across the midline, shielding frontal body parts, and its tailfan bent downwards. The mean claw cocking duration (generating muscle tension) before snapping amounts to about 500 ms. In 58% of the snaps, the snapper claw pointed at the opponent, its claws, densely covered with sensory hairs, representing the main target of the water jet. The mean distance for these directed snaps was 0.9 cm, while undirected snaps were emitted from larger distances of on average 3.4 cm. The snapper usually withdraws immediately after snapping, the receiver approaches. Initial snaps are often answered by return snaps and both are emitted from smaller distances and hit more often than subsequent snaps.