The sessile animal is usually fixed to the sea floor by an attachment disk, with its fan-like crown of arms supported by a tether-like stem.
The arms are arranged in a parabolic fan that faces into the prevailing water current and have numerous rows of feather-like pinnules which are covered in podia. The podia are shaped like small tenticles and bear long, slender, mucus-secreting papillae.
During feeding, food:
Proisocrinus ruberrimus is sessile, limited to bending movements of the stalk and flexion and extension of the arms. Like many other crinoid species it has muscular articulations in the arms that would allow the animal to crawl across the sea bed, but this behaviour has only been observed in other, shallow-dwelling, species.
These crinoids occur in relatively isolated small colonies on rocky substrates. The high frequency of regenerated arms suggests that they are subjected to frequent non-lethal predation.
Due to its rare occurrence, it is not known if Proisocrinus ruberrimus is affected by parasites or disease although many other crinoid species are.