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.