Hi Luis, hope you don't mind me jumping onto your post. Just thought a clearer picture of zoea I larvae would be of interest to other viewers. My larvae was curled up though, different from your stretched out photo.
I have not heard anything about the 23 day mark so far. Maybe deaths during that time occur due to overcrowding? I have a batch of L. amboinensis larvae now around 55 days, all with very visible pleopods already. I raised about 36 of them in 3 liters for the first 3-4 weeks, after which I halved their stocking density. So far out of the 36 only 2 died. One was crushed by the airstone when I put it down while the other died of natural causes. It was a different experience when I was rearing them in high densities in fish tanks. By 55 days you would be lucky if you even had 50% survival.
L. amboinensis and L. wurdemanni are from the same genus as far as I know of. At least that is what many publications say. Different species will develop differently and will have different number of larval stages. The long appendages don't appear to break when they first appear. Only starting when they get longer and longer, usually beyond 30 days. I suspect this breakage occurs during moulting. I have seen a larvae in the midst of moulting once and apparently the moult comes of the 5th periopod last. The moult could have been the stress factor for the frequent loss of the 5th periopods.
I doubt the water volume is the key. Most probably it has to do with water current somehow. I had many large ones in an upwelling system that all failed to settle, although they grew much much faster compared to larvae in tanks. Some larvae (about 5 or so) from the same batch were taken from the upwelling before the die-offs occured and placed in a small glass aquarium (probably only 6 liters at max). A simple airstone was set on low output. Viola the first larvae settled at 150 days. The rest died though, the person who was in charge of caring for them during the vacation overfed the tank.