Spiny Roj

The spiny roj split from its ancestor. The spiny roj live in far smaller swarms than their ancestors, move in clusters, not sheets and are reacting more passively to predators, as the spines make them very hard to swallow without getting damaged or prevent swallowing altogether. Additionally, the spines are hollow and can filled with metabolic gas or fluids, working as a hydrostatic device. Like their ancestor, they keep their young first in their central chamber, before they release them. The young are staying close to the adults, often using their fins to attach themselves to the shell of the elders and join the outer groups of juveniles after a certain age. Spiny rojs are more present in areas with more predators, where they have a bigger advantage due to their protection, which doesn't put the juveniles in danger, but get out competed by the larger rojs wherever predation is low. The size range of ingested food particles lies between 2 mm and 100 µm diameter.