Feather stars, or crinoids, are ancient marine invertebrates belonging to the phylum Echinodermata, making them relatives of sea stars and sea urchins. A recent discovery in the frigid Southern Ocean introduced a striking new member of this group. This deep-sea resident, named the Antarctic strawberry feather star, captured public attention due to its unusual appearance.
Defining the Strawberry Feather Star
The organism is formally classified as Promachocrinus fragarius, establishing it as a newly recognized species of Antarctic crinoid. This feather star is a motile, stemless type known as a comatulid, meaning it does not have a permanent stalk anchoring it to the seafloor. Its classification emerged from a comprehensive taxonomic revision of the genus Promachocrinus, which was previously thought to contain only one widespread species. The study used a combination of detailed morphological analysis and molecular sequencing of the mitochondrial COI gene to distinguish P. fragarius from its relatives, revealing significant, previously hidden diversity. This new classification effectively separates P. fragarius and three other newly identified species from the formerly recognized single species, Promachocrinus kerguelensis.
The True Dimensions
The most remarkable feature of the Antarctic strawberry feather star is its high number of appendages, a factor that directly contributes to its overall size. This species possesses a total of 20 arms, which is double the arm count of many other feather star species. The arms themselves can reach a considerable length, with some specimens having appendages that measure up to 20 centimeters (approximately 8 inches) long. When fully extended, the total arm span, or radius, of the creature is estimated to be approximately 40 centimeters (about 16 inches) across. The central body, or theca, is relatively small in comparison to the arms; this strawberry-sized calyx serves as the core from which the multiple arms and anchoring structures radiate.
Appearance and Coloration
The common name, Antarctic strawberry feather star, is derived from the unique appearance of its central body, known as the calyx or theca. When the cirri (small, claw-like appendages used for clinging) are removed, the main body structure has a rounded, bumpy texture that strongly resembles the shape and surface of a strawberry. The scientific name itself, fragarius, comes from the Latin word for strawberry, fragum, alluding to this fruit-like structure. Specimens often display pigmentation ranging from purplish hues to a dark, reddish color, which is typical for many creatures living at these depths. The 20 arms are feathery in appearance and are described as having two distinct types: lower, shorter arms that appear bumpy and upper, longer arms that look more padded and soft.
Habitat and Movement
Promachocrinus fragarius is found exclusively in the cold, deep waters of the Southern Ocean, inhabiting depths that span from approximately 65 meters (213 feet) down to 1,170 meters (3,840 feet). The crinoid is a motile organism, utilizing its multiple, flexible arms for both movement and feeding. It is capable of crawling along the seafloor or briefly swimming through the water column, achieving movement by the rhythmic flailing of its numerous arms, which creates a mesmerizing, undulating motion. The feather star is primarily a filter feeder, using its extensive crown of feathery arms to capture tiny plankton and suspended organic particles that drift through the deep-sea currents. The small, clawed cirri on the calyx allow the animal to anchor itself temporarily to the substrate while it feeds.