Ecological studies on the Japanese mantis shrimp, Oratosquilla oratoria (DE HAAN). II. Egg laying and egg mass nursing behaviour in the Japanese mantis shrimp.

The spawning and egg mass nursing behaviour, together with the change in external appearance of the egg mass, of the mud-dwelling Japanese mantis shrimp Oratosquilla oratoria were studied using artificial burrows in aquaria. This species usually spawns in a supine posture in the burrow maintaining this posture with the back of abdomen and exopods of uropods against the wall of burrow for almost 3 h. The newly extruded egg mass is amorphous, but the female shrimp compacts it and then shapes it into a thick disc within 1 h and to a thin disc having a marginal turnup within 24 h of spawning. All maxillipeds excluding the raptorial claw are used for the nursing behaviour, i.e. spreading and folding the egg mass, so it is teased out and becomes a tuft shape after 3 days or so. The second gee laying occurred in 2 females about 40 days after the first spawning of each individual at 25°C, and this fact suggests that O. oratoria may spawn more than once in a spawning season in natural warm waters.