A matriarch fades away, but the next generation reaches maturity.  

At this point, it is a familiar cycle.  They start out as a members of an egg mass, with thousands of their siblings.  After they hatch, a lucky few dozen or maybe a hundred settle down and feed, selected mostly on the basis of luck.  Once they start feeding, they grow rapidly, and a smaller, luckier group gets to go home to Box of Slugs 2.  These will be allowed to get large and produce the next generation.  And so on.

The previous generation has now come to an end.  Several slugs from a brood laid in early January 2019 were placed in the tank on May 1. 

Matriarch in her prime. July 1, 2019.

After growing to the usual big size, and laying many clutches of eggs over several months, the last of the group started to fade in late January 2020.  

Elysia clarki at one year old. Hatched about 1/25/19, photographed 2/2/20. Note yellow parapodia and faded green body.

The biology underlying the change is unknown, at least to me, but I assume that the slugs fail to maintain or replenish their chloroplasts for some reason. Regardless of the cause, it seems to be a one-way street, and the old Elysia become more yellow, shrink, and start to look unhealthy.

Even in her last days, the old female appeared to feed on the available Bryopsis alongside her daughters, but she was unable to either absorb or process the food. Within a few days, she had disappeared. When a body is almost all water, it does not last long after death. She lived for over a year, which is not close to the record of two years reported by Pierce and colleagues, but is a pretty good life for a sea slug.

Fortunately, life also involves renewals. Over the summer and fall, the slugs produced thousands of eggs, and some of the offspring have matured to produce eggs of their own.

A pair of young slugs from a brood laid on 9/24/19 has produced their first clutch of eggs. As is usually the case, the first egg mass is smallish, maybe a few hundred eggs, but the size will rapidly increase. Production of the first eggs at four months of age is also consistent with previous observations.

So we are, once again, coming full circle. I need to sit down at some point and count how many generations have passed since the first hatchlings survived and grew into baby slugs, but it is satisfying that the group can keep itself going.