Swarming detritustar replaced its ancestor, adapting further to benthic coastal habitats and spreading into coastal wetlands with variable salinity. It is smaller with reduced fingers and elongated whiskers. The front 2 arms are more specialized for feeding, having shifted closer to the mouth. The back arms are used exclusively for swimming and have longer whiskers. The photoreceptors are further apart to accommodate the shifted arms and provide a wider range of vision.
Reproduction is different from its ancestor in several ways. Individuals can determine the sex of others with a chemical signal emitted from the cloaca into the surrounding water. This can be detected within close proximity by chemoreceptive cells in the mouth. This sexual communication reduces costly and fruitless mating encounters. During mating, the anal arms' whiskers come together to align the cloacas, which have moved further down the arm, for a cloacal kiss.
Most mating occurs during times of higher-than-usual food availability and warm temperatures. During this time, population booms and mating frenzies can produce dense swarms that exceed a cubic meter in volume.