In the depths of our oceans, mysterious and enchanting creatures known as sea lilies and feather stars gracefully dance and sway, capturing everybody’s imagination. Although looking like plants, these fascinating species have a close relationship with sea stars and sea urchins. Join us on a journey into the enigmatic realm of these captivating organisms as we unravel interesting facts about these crinoids – the wonders that lie beneath the waves.
Class: Crinoidea
1. Sea lilies and feather stars appeared 490 million years ago
The sea lilies and feather stars, also referred to as crinoids, bear a striking resemblance to plants. However, they are indeed animals, distinguished by their spiky surface. They just share a close relationship with sea stars, sea cucumbers, sea urchins, sand dollars, and other members of the phylum Echinodermata, exhibiting five asymmetrical and radiating arms.
Sea lilies and feather stars possess a remarkable and extensive evolutionary past, spanning more than 500 million years since the Cambrian period. Their origins are traced back to cystoids, a now-extinct echinoderm group that flourished during the Devonian period. While these captivating beings were once widespread, today they predominantly inhabit the deep waters of the Caribbean Sea and the Atlantic Ocean, typically residing at depths of 200 meters or greater.
Here are some prehistoric crinoids in the form of fossils: (Cre: Fossilera)
Crinoid columnals
Fossilized stem segment of a columnal crinoid is called Indian bead
Crown crinoid fossil
Scyphocrinites crinoid
The Jimbacrinus bostocki crinoid
Crinoid fossil with a complete head
Crinoid holdfastOnce abundant, these species have become a rarity. Nowadays, encountering a fossilized crinoid is more common than finding one that’s still alive. Currently, approximately 700 recognized living crinoid species exist, categorized into two primary forms: those possessing a stem and those without. Those without stems are called feather stars, whereas crinoid species with stems display a remarkable similarity to flowers, called sea lilies.
The largest crinoid ever is the fossilized Encrinus liliiformis featuring a stem measuring 40 m (130 ft) in length.
2. They look like a bunch of feathers
The sea lily bears a resemblance to a delicate flower with 5-ray symmetry. Surprisingly, despite their fragile look, these crinoids possess a sturdy outer skeleton to give them better protection. In contrast to typical crinoids, sea lilies possess a distinctive stalk comprising stacked plates, enabling it to affix itself to diverse surfaces like the ocean floor, rocks, and corals.
The uppermost part of the stalk forms a circular center called a calyx, housing essential organs, including reproductive organs, the digestive system, and the mouth. This calyx is encircled by five to ten slender arms that can be separated from one another. Their branching arms are covered in cilia. There are about 80 sea lily species.
The feather star exhibits resemblances to the sea lily. Nonetheless, they differ in their mode of mobility, as feather stars lack the elongated stalk found in sea lilies, allowing them to swim freely. Distinguishing them further from other echinoderms, feather stars boast numerous arms, ranging from 10 to 30. Some feather star species can even have 200 arms. These arms are adorned with pinnacles running along each side, giving them a feathery appearance.
Feather stars possess the remarkable ability to adapt to the position of their arms. During resting time, these animals tend to curl their arms inward.
The average size of these species is approximately 12 inches (30 cm). Feather stars exist in a diverse array of more than 600 types, showcasing a striking spectrum of colors. Among them, vibrant hues like bright yellows and reds serve as a warning to potential predators. Some of them are elegant feather star, and rosy feather star (Antedon bifida).
3. Diet
Sea lilies and feather stars are suspension feeders, primarily feeding on living organisms, with a particular fondness for invertebrate larvae. Additionally, they forage on the ocean floor, scavenging the remains of deceased organisms.
These species will look for an appropriate location. Although lacking stalk, feather stars have a disc-like sucker on their feet, this adaption allows them to grasp onto surfaces.
At these spots, they will extend their arms into the passing current. Their feather-like arms adorned with small tube feet are coated in mucus. When these arms come into contact with anything, it becomes ensnared. The captured prey is then transported along specialized channels toward their mouth.
Sea lilies and feather stars do not possess a true stomach. Instead, the food they eat travels directly from their mouth to the esophagus and then into the intestine. Eventually, the food reaches the rectum and anus, which are both situated on the same surface as the mouth.
Sea lilies, being ectothermic organisms, have a metabolism strongly impacted by water temperature. With an increase in water temperature, their metabolic rate rises, facilitating more efficient food processing. But excessively high water temperatures can push their metabolic rate to dangerous levels, causing them stress and even possible fatality.
Other factors, such as light, activity level, and food availability, also play a significant role in influencing their metabolic rate. When exposed to bright light and provided with ample food, their metabolic rates increase. However, since they tend to stay in one place, their metabolism rate is lower than other animals.
Crinoids face threats from various predators in their marine habitat, such as fishes, crabs, sea stars, and sea urchins. Additionally, smaller organisms like snails, crinoid shrimps, and worms may take up residence on feather stars and occasionally feed on them.
To defend, sea lilies and feather stars use the same technique as that of starfish. They detach their arms when under attack. Surprisingly, the detached arm persists in twitching, serving as an intensified distraction during the escape. These lost arms can be regenerated in a month.
4. Habitat
Sea lilies and feather stars are solitary creatures, living in oceans all over the world. Sea lily once lived in both shallow and deep waters, with a particular fondness for depths ranging from 100 to 1,000 meters. However, present-day observations reveal that their distribution has changed significantly, and now they are predominantly discovered in profound depths of approximately 200 meters or beyond.
These organisms affix to solid substrates like rocks and coral reefs through their stalks, forming expansive “underwater forests” on the seafloor that serve as crucial ecosystems.
Feather stars span from temperate to tropical environments and extend into polar regions. These fascinating crinoids can be found at depths ranging from the ocean’s surface to an astounding 30,000 feet (9,000 meters). While they thrive in various locations, they are particularly abundant in the Indo-West Pacific region.
Sea lilies and feather stars are nocturnal. Throughout the day, they find refuge beneath coral ledges or within the shadowy recesses of underwater caves. Yet, as night descends, they venture forth, migrating to shallower waters in search of food.
5. The sea lily can move
Beautiful feather stars, lacking a stalk, often move across the ocean by using their arms. Their swimming capability is restricted to short bursts of about 30 seconds and covers only limited distances. These modern crinoids only move about 5 – 7 centimeters per second. This speed is influenced mainly by factors such as gender, the presence of predators nearby, and inherent tendencies.
On the other hand, sea lilies often anchor themselves to surfaces for most of the time. However, they will move when confronted with dangers or predators. In such situations, they will detach a small section of their stalk, allowing them to liberate themselves from the ocean floor.
This ability enables ocean lilies to get away from dangers by crawling with their cirri (legs) or swimming through the water with their arms. These movements are particularly prevalent in juvenile sea lilies, as they exhibit greater mobility compared to their adult counterparts.
6. They don’t have a brain or heart
Sea lilies and feather stars do not possess a heart or a distinct circulatory system. However, they do feature a substantial blood vessel known as the axial organ located at the disc’s base. Oxygen primarily gets absorbed through their delicate tube feet, while gas exchange takes place over the extensive surface area of their arms.
Crinoids, similar to other echinoderms, possess a water vascular system responsible for functioning their tube feet in both arms and pinnules. However, their system is not linked to the external seawater; instead, it connects to their body cavity through pores.
7. Reproduction
Sea lilies and feather stars showcase captivating reproductive and life cycles, with reproduction taking place roughly every 10-16 months.
In their reproductive process, the males and females will release their eggs and sperm into the water, enabling fertilization to occur. Following fertilization, the eggs hatch into larvae, which then float freely in the sea current, nourishing themselves with plankton and other tiny creatures in the water.
As these creatures mature, they experience a metamorphosis and take root on the seafloor, transforming into stalked juveniles. Once they reach adulthood, sea lilies stay firmly attached to the seafloor, while feather stars eventually detach themselves from the stalk.
The lifespan of sea lilies and feather stars varies significantly based on their species and the environmental factors they encounter. Feather star lifespan is about 15 years. The lifespan of sea lily species can endure for up to 80 years, whereas other species can only live for a few years.
References:
- Oceaninfo.com
- Americanoceans.org
