These animals were not housed permanently in an aquariusm. I had just caught them hours before on a reef flat off Lizard Island (Australia) and placed them in a small, 1 gal photographic aquarium. They were released shortly there after. Pseudosquilla ciliata, like Odontodactylus scyllarus, will mate any time in the females reproductive cycle and females actively solicit copulations from males.
A male and female O. s. will often coexist for days or even weeks in an aquarium, often sharing for the same burrow. However, there is always a risk. If one molts or the female is ready to lay eggs, a fight can break out and it is not uncommon for one to kill the other if it can't escape. If you want to mate them, the simplest solution is to divid a tank (we use plastic egg crate, although they eventually will break through it) and periodicall pull the partition. The animals will usually mate within minutes. You can then chase them back to their respective sides and replace the barrier. I would say the the minimum size needed to support two midium sized O.s. (4-5 inch), provided that the tank is really functioning well, is 20 gal. Even here there is a risk if you miss some uneaten food.
Roy
