Polycera atra - mating juveniles

Dear Mike,
Even for California I must say I think mating at 2 mm is a bit extreme. It does however illustrate how the reproductive system develops in these animals. I have no personal knowledge of this species but often when dissecting juvenile nudibranchs we will find that at a very early stage, even before gonads are visible, there will be a little tangled mass of ducts, which represent the primordial 'plumbing' of the reproductive system. At this stage the associated glands have not developed. Usually the first part of the reproductive sytem to develop in these hermaphrodite animals are the male organs - the testis and penis - and often in half developed animals sperm from another partner will be found packed in a sperm sac, suggesting that animals can exchange sperm before they have mature eggs to fertilise.  I don't think we know whether they can keep the sperm alive and functional until their own eggs mature, but if so, it would be a useful survival strategy. In many cases, it is the juveniles which are found in large aggregations - often hatching together, or settling together from a larval swarm. Many will die before maturity, so if they can exchange sperm at this early stage, and store it for some time, it is not so critical if only a few survive to maturity, or if as adults they have difficulty in finding a partner. It is a very interesting observation.
Best wishes,
Bill Rudman