Bonechewer Oysters
Oysters struggled immensely during the Time of Hunger, forced into the thin wedge between anoxic waters and hungry rats. Once the Hunger subsided they soon bounced back, and with no molluscivores in the environment, they began to radiate into strange new niches.
Oyster larvae are ejected into the water column, where they drift and (hopefully) eventually settle onto a hard surface that the adult oyster attaches to- they cannot live in soft substrate. Due to the Hunger the drifting larvae found a strange and abundant habitat on which to grow: skeletons.
The countless trillions of dead fish from the Hunger had resulted in the coastal sea floors being covered with skeletons, in some places tens of metres deep with bones. Many of these bone beds still lay exposed, too thick for swept sediment to cover. These surfaces provided a nice anchorage point for the larvae, and colonies soon sprang up.
Oyster shells are constructed from calcium, and the enormous reservoir of calcium the oysters themselves were sitting on did not go unnoticed. Bonechewer oysters have- effectively- evolved to *eat* the bones they grow on. A settled larvae uses its cilia to scrape off a tiny bit of bone, which provides it with both a little nook on which to settle and a source of calcium with which to build its adult shell.
In adults the cilia are much more pronounced, extruding from the shell and able to extend some distance beyond. The ends of the cilia are covered in microscopic hooks, which are used to ‘lick’ the surrounding bones, scraping up minute pieces of calcium which are then ingested. The bonechewer is not fussy and will on occasion lick its neighbour; this is however counterproductive as it also means the neighbour is in range to lick them back. Neither benefits from this recursive shell stealing.
A side effect of this calcium ingestion is that- eventually- the skeleton underneath the oyster will not be able to support the shell’s weight and will collapse. If buried out of the way from the flowing waters with which it needs to filter feed the oyster will gradually starve and die, its shell becoming another anchorage point for future larvae.
As a result of the preference for calcium-rich substrates bonechewer oysters have begun to form the world’s first reefs, as generations upon generations settle and grow their shells on top of each other. As the reefs are also being eaten they grow slowly, but provide a permanent hard substrate island on the sea floor; an excellent habitat for small invertebrates.