The Feather Starfish

feather stars are marine animals that make up the class Crinoidea. feather starfish that are attached to the sea bottom by a stalk in their juvenile form are commonly called sea lilies, while the unstalked forms, called Crinoids or comatulids, are members of the largest crinoid order, Comatulida.

Scientific name: Crinoidea

Phylum: Echinodermata

Domain: Eukarya

Kingdom: Animalia

Habitat

There are approximately 625 different species of feather stars, and are found in almost all the oceans and at all depths. They are found in the tropics, temperate and polar zones often found sheltering by day under coral ledges or overhangs with their feathers rolled up. When night falls, these filter feeders migrate to the top of the reef and extend their arms into the currents where they trap fine particles and planktonic food using their net-like arms.

Life cycle

These marine animals reproduce every 10-16 months. Reproduction consists of a larval stage, free swimming period, and pinnule stage. Male and female creatures often live in different habitats, which makes breeding periods unique to the colony. Natural events are particularly dangerous to the species, as their life cycles depend on strict timeframes. If a mating season is disrupted, the nearby population could be in jeopardy.

Diet

These animals are suspension feeders, trapping small particles with their mucous-tipped tube feet before routing them through a complex series of grooves and into the mouth on the central disk. They feed for several hours daily and in such copious amounts that they are difficult to maintain in captivity, requiring continuous high concentrations of the correct types of plankton in order to survive.

The bulk of the feather star’s nutrition comes from living things, though they do trap and consume non-living organic particles and plant material, such as diatoms. These organisms have a demonstrated nutritional need for zooplankton, both in the form of foraminifers, or marine protozoa, and small or larval mollusks and crustaceans. Although they might technically be considered omnivorous, captive experiments have shown that feather stars extract approximately 80 percent of their energy from invertebrate larva, placing them firmly into the realm of carnivores.

Because feather stars do not have an official stomach, consumables cycle through their body in waves while still providing nutrition. Crinoids produce waste that quickly dissolves into nearby corral or rocks.

Here are five of the most beautiful species from around the world,

Rosy Feather Star.

Only found in deeper water, feather stars spend most of their time anchored to the seabed, seaweed or sometimes sponge, using extremely strong claw like appendages. They are suspension feeders, sifting out bits of plankton from the surrounding seawater using their tube feet, a characteristic of all echinoderms!

How to identify

Ten feathery arms, 5-10cm in length and usually red and white in color, sometimes looking mottled.

Promachocrinus Kerguelensis,

Promachocrinus kerguelensis is a species of free-swimming, stemless crinoids. It was the only member of its genus until several species were discovered in 2023. P. keruguelensis a coldwater crinoid which is found in the seas around Antarctica and surrounding island groups, including under the sea ice.

Antedon Petasus,

Members of the class Crinoidea are gonochoric. During spawning, the pinnule walls rupture and the eggs and sperms are shed into the seawater.

Life cycle: Embryos elongate into free-swimming larvae (doliolaria) which later sink to the bottom where they metamorphose into stalked sessile crinoid.

Comaster Nobilis,

Comaster nobilis can reach a diameter of about 40 cm (16 in). It has a cup-shaped body with 35-40 arms, extended out from the central disc. This species may occur in a number of colour variations. Usually it has yellow arms, sometimes with some black or green and white on the under surface close to the centre. It feeds on detritus, fitoplancton and zooplancton. The larvae of this feather star swim freely with plankton for a few weeks, then they settle down growing into a stalked form. Mature specimen break the stalk becoming free-living.

Oxycomanthus Bennetti,

Oxycomanthus bennetti is one of the larger species of Comatulidae, growing up to 30 cm. It is a filter-feeder, meaning it does not hunt down food, it captures food suspended in the water column to eat. It does this with 31–120 feathery arms, usually held up into the water in order to trap food, feeding on detritus, phytoplankton and zooplankton. The arms have numerous finger-like appendages known as pinnules, in order to increase the surface area on which food can be trapped. The mouth is on the upper side of the large, thick body, otherwise known as the centrodorsal. Attached to the centrodorsal are many long, robust cirri (3-4.5 cm). These cirri are used by O. bennetti to hold on to substrate in the beginning portion of their lives, after the larvae settle out of the water column. They begin their lives attached to a stalk, held onto a substrate by cirri, and once mature, they can break the stalk and become free-living. Once they are free-living, however, they still use these cirri to elevate themselves to put themselves in a better position to trap food. Because these cirri are so long and robust, the posture of O. bennetti can be used to easily distinguish it from other similar species. O. bennetti is diurnally active, meaning it is active during the day, unlike many other species of crinoids. The color of this species is quite variable, ranging from yellow to brown and purple. The tips of the pinnules are often more brightly colored than the arms and centrodorsal.