At certain times of the year, we have extraordinary luck finding nudibranchs that inhabit the blades of giant kelp or other types of low-growing algae or bryozoan. The adults can be very small, well-camouflaged and easily overlooked, but their luminous white eggs give them away.
Delicate strings, flat whorls, wide ribbons, and glistening orbs contain developing embryos that herald another generation of nudibranchs. During these chance encounters, I imagine that I’ve caught a glimpse into their ephemeral lives.
Nudibranchs are hermaphrodites, that is, they possesses both male and female reproductive organs. During copulation, the slugs orient themselves so that their genital apertures meet. After reciprocal insemination, each slug may lay eggs.
A delightful feature of nudibranch eggs is that each species seems to have a patent on their particular style, shape, size or color of egg mass.
Corambe pacifica and Corambe steinbergae competitively feed on the bryozoan, Membranipora membranacea, where they settle and reproduce at the same time. Although closely related and very similar in appearance, they produce quite different egg masses.
After an egg mass is laid, the embryos of most species develop fairly rapidly, roughly in 1 – 2 weeks. In 91% of 126 west coast benthic species, what hatches from the egg is a larvae that does not resemble the adult. Rather, the embryo develops into a shelled veliger larvae, no larger than 1/10th – 1/20th of a millimeter.
The nearly transparent veliger larvae have protective shells and a ciliated velum, which is used for swimming, food particle collection and concentration. Veligers automatically propel themselves upwards in order to prey on single-cell algae near the surface. Larvae are pelagic for some time during their development are planktotrophic.
A planktonic larval veliger is the transitional state before becoming a recognizable slug. After developing sufficiently, and when the veliger reaches a state of competence, it responds to a chemical signal from its preferred food source and settles to the bottom. In a day or so, it metamorphoses into a juvenile slug.