The giant larvacean's unwanted cage is destined to become a particle of marine snow, its contribution to the recycling of ocean nutrients. Tumbling end over end, the discarded house slowly floats downward. In the photic zone of the open sea--the upper layer of ocean, in which sunlight penetrates enough to allow plants to grow--the turbulent water slams unicellular algae onto the sticky walls. A free-falling shell fragment from a dead crustacean whirls around the abandoned house and lodges in a mucousy crevice.

image courtesy NASA