Crinoidea

(Sea lilies and feather stars)

Phylum Echinodermata

Class Crinoidea

Number of families 25

Thumbnail description
Stalked or stalkless organisms with a crown composed of a calyx, five or multiple arms, an anal cone, and a mouth pointing upward

Evolution and systematics

Crinoids are a living lineage of echinoderms more than 500 million years old. The first crinoids were stalked forms (the sea lilies), whose probable ancestors are the extinct rhombiferans or the extinct edrioasteroid echinoderms. The first fossil record dates from the Lower Ordovician (510 million years ago[mya]). During the Paleozoic era (550–245 mya), there were at least two major expansions and declines in crinoid diversity. In the early Carboniferous (360 mya) crinoid diversity reached its zenith, exceeding the total diversity of all other echinoderm taxa. During the Permo-Triassic extinction (240 mya), the crinoids suffered a catastrophic decline and only one lineage survived, which gave rise to the earliest subclass, Articulata. Throughout the Mesozoic era, this lineage had begun to diversify and, about the time of the early Jurassic (210 mya), the order Comatulida (stalkless crinoids, the feather stars) appeared. The disappearance of stalked crinoids from shallow waters and their restriction to deeper sites coincides with the Mesozoic radiation of predatory bony fishes. About 6,000 species of crinoids have lived and died out in past geological ages.

There are about 600 feather star species distributed among 150 genera and 17 families in one order, and 95 extant sea lily species distributed among 25 genera (50% of them are monospecific), 8 families, and 4 orders. The living crinoids orders are: Millericrinida, Cyrtocrinida, Bourgueticrinida, and Isocrinida (all sea lilies); and Comatulida (feather stars).

The class Crinoidea is the ancestor group of all other echinoderm classes. The relationships among extant orders are still obscure, but some attempts have been made to elucidate them. Among the orders, Millericrinida and Isocrinida are the most ancient. The comatulids diverged from a group of Isocrinida, and the bourgueticrinids, due to the retention of larval stem, diverged from the comatulids. Cyrtocrinids possibly diverged from the millericrinids.

Physical characteristics

Crinoids are pentamerous organisms that differ from other echinoderm classes because of the upward position of their mouth. Numerous calcareous plates, more or less firmly joined together, form their endoskeleton. The main body part is the crown, which is made up of the calyx, the tegmen, and the arms. The calyx, a rigid cup formed by the calcareous plates, carries the digestive tract, the mouth, esophagus, gut, rectum, and anus. An upper membrane, called the tegmen, bears the openings of mouth and anus and is perforated by numerous small pores that connect the interior of the crinoid with the external environment. The mouth is usually located near or at the center of the tegmen, although it is displaced peripherally in the family Comasteridae. The anus, displaced from the center, is elevated at the tip of a cone or tube. In all but adult comatulide there is a cylindrical or polygonal stalk (stem, column) below the crown, which elevates the crown above the substratum. In comatulids, a cluster of appendages, called cirri, takes the place of the column. The cirri may or may not be present along columns of stalked crinoids. All crinoids have five arms, developing from the calyx, that usually branch one or more times, giving rise to up to 200 arms. Small branches called pinnules border each arm. Those nearest to the month are called oral pinnules. Gonads usually occur in the next group of pinnules, called the gonadal pinnules, although they may also occur in the arm axis, but almost never in the central mass of the body. After the gonadal pinnules are the so-called distal pinnules. Ambulacral grooves (food

grooves) occur in the oral surface of the calyx and reach the distal extremity of each arm and pinnule. Ambulacral podia (tube feet) line each groove, but the pinnular podia are organized in groups of three podia of different sizes (each podia with different functions during feeding).

In living crinoids, the arms range in size from 0.39 to 13.8 in (1 to 35 cm), depending on the species. The stem of living sea lilies reaches about 3.3 ft (1 m) long, but was much longer in some fossil species, up to more than 65.6 ft (20 m). Comatulids may be of almost any color, white through black, purple, red, green, brown, or violet. The species may be uniform in color or have a combination of colors. Usually, the deeper the organism, the paler the color.

Distribution

Crinoids are found from substidal fringe zones to great depths in tropical, temperate, and polar waters, although they are more diversified in coral reefs of the tropical Indo-Pacific and Caribbean (although fewer species are present in the Caribbean). Stalked crinoids are restricted to the deep sea, with just a few species living at depths of 200–490 ft (60–150 m). There are three major areas of sea-lily biodiversity: the tropical West Pacific, where three members of the order Isocrinida predominate, the pentacrinids at 660–1,970 ft (200–600 m) and the bathycrinids and hyocrinids at 4,920–9,840 ft (1,500–3,000 m); the tropical western Atlantic, where more diversity occurs at upper water levels; and the Northeastern Atlantic, where more diversity occurs at a deeper water level.

Habitat

Crinoids frequently live on hard substratum. Some live in areas of high current flow, usually use the vertical filtration fan posture (described in the next section). Others avoid high streams and use the radial feeding posture. Nevertheless, crinoid community is probably determined by substratum complexity, independent of water flow. A highly complex substratum may trigger a high diversity crinoid community, and a homogenous substratum carry a low diversity crinoid community.

Behavior

Feather stars usually live in clumps, preferring to attach to crevices, lateral surfaces, or in other places in which they can hide their central mass. This behavior prevents and avoids injuries to vital body parts caused by predators, and also optimizes filtration by enhancing the baffle effect, which improves the chance of food particles touching the feeding structure. They frequently emerge at night, exposing part, or all of, the arm, or even the entire body, although some species emerge during daylight, and others are exposed both during the day and at night.

Stalked crinoids also occur in dense clusters, but do not have a diel pattern of emergence because of the lack of light in deep water. Most can also be found attached to a hard substratum. The depth distribution of stalked-crinoid diversity seems to be controlled by variations of both crinoid hydrodynamic vulnerability and abundance of food particles reaching the sea floor.

Crinoids can also regenerate lost body parts. Feather stars can regenerate their arms as long as at least one arm and an intact dorsal nerve center remain. Sea lilies can regenerate an entire crown.

Feather stars are able to crawl over the substratum utilizing their arms. Some comatulids have been observed swimming. They swim by alternating their arms up and down, and descend through the water by extending their arms out like parachutes. Only a few sea lilies are able to crawl over the substratum, and none have been observed swimming.

Feeding ecology and diet

Feather stars assume a vertical filtration fan posture in areas of high current flow. In this posture, the arms are deployed in a planar fan, with pinnules held in the same plane and the food grooves usually directed downstream. The vertical filtration posture serves to present the maximum cross-sectional area of food-collecting surfaces to the incoming water flow, and also acts to baffle through-flowing water, possibly

facilitating the capture of food particles by the tube feet. Sea lilies assume a similar feeding posture, although they recurve their arms almost 270° upstream to form a parabolic filtration fan. The mouth may be oriented laterally downstream, with the food grooves also turned downstream, or it may be oriented upward in slack currents. Feather stars living in low-current areas use a radial feeding posture, orienting their arms in many directions with the pinnules extended radially in four rows. The radial feeding posture serves to maximize the surface area of the feeding structures so that more particles will settle on them.

The crinoid diet consists of phyto- and zooplankton and detritus, and varies with habitat and seasonal availability. The size of the particles captured depends on the width of the food groove. The primary podium (the largest in the group of three) collects particles in the water column and folds them back into the groove. Relatively large particles are captured by podia partly curling over them; small particles adhere to the mucous layer. The podia transfer the particles to the food groove by brushing them away with the ciliary tract or the tertiary podia. The secondary podia behave as the primary and secondary podia do, collecting particles in the water column and folding them back into the food groove.

Reproductive biology

All crinoid species are gonochoric (although some individuals may present hermaphroditism), and they probably do not reproduce asexually. Depending on the species, the ova vary in size from 0.004–0.012 in (100 to 300 µm). The maturing oocyte enters the ovarian lumen through a temporary opening in the layer of nongerminal cells in the inner epithelium, a process called ovulation. Inside the ovarian lumen, the oocytes undergo two maturation divisions and become ova. Crinoids take 12 to 18 months to reach maturity. The gametogenic cycle usually takes one year, although in some species it takes several months and in others takes almost three years. The spawning season, the period of the year during which gametes are released, varies among species and populations of each species and can last from one hour to many months.

Sperm are released directly from the testes into sea water. Females of most species also spawn freely into sea water, but in some feather stars, the ova are retained on the outer surface of the mother's genital pinnule. In these species, the ova may be kept for days and then released, or may enter into brood pouches (where such pouches exist). Almost all crinoids develop by lecititrophic larvae (short-lived, nonfeeding, planktonic larvae called doliolaria larvae) followed by a benthic, nonfeeding, stalked stage that metamorphoses to a benthic stalked juvenile. Most crinoids have only doliolaria larvae, which are ovoid with four or five transverse bands of cilia and a tuft of apical cilia. Only one species is known to have internally brooded vitellaria larvae, which lack the ciliated bands.

Conservation status

No species are listed by the IUCN.

Significance to humans

None known.

Species accounts

List of Species

Rosy feather star

Antedon bifida

order

Comatulida

family

Antedonidae

taxonomy

Antedon bifida Pennant, 1777, western coast of Scotland.

other common names

None known.

physical characteristics

Feather star with 10 arms, 2–4 in (50–100 mm) long; pink, red yellow, or orange, frequently banded, usually with white pinnules.

distribution

Northeastern Atlantic, from Shetland Isles to Liberia and west to the Azores. Intertidal zone to 1,476.4 ft (450 m).

habitat

Lives in current-agitated shallow water attached to hard substrata, such as cliff faces and boulders.

behavior

Broods offspring by bringing the arms near the body and folding the pinnules against the arm axis.

feeding ecology and diet

Feeds through the vertical filtration fan posture.

reproductive biology

On the external wall of the genital pinnules, females brood their eggs in a mucus net until they hatch as early larvae. Spawning occurs in late spring, although mature gametes may occur for many months throughout the year.

conservation status

Not listed by the IUCN.

significance to humans

None known.

No common name

Oligometra serripinna

order

Comatulida

family

Colobometridae

taxonomy

Oligometra serripinna Carpenter, 1881, Andai, New Guinea.

other common names

None known.

physical characteristics

Feather star with 10 arms, 0.4–1.8 in (10–45 mm) long. Proximal pinnule segments longer than they are broad; yellow to orange.

distribution

Western Indian Ocean to the South Pacific, through the Great Barrier Reef. From at least 20–80 ft (6–25 m) in depth. (Specific distribution map not available.)

habitat

Usually fully exposed on unsheltered perches and attached on hard substratum.

feeding ecology and diet

Feeds through the radial filtration fan posture.

behavior

No diel pattern.

reproductive biology

Probably reproduces twice a year, around February and June. Spawns freely on sea water and develops through lecititrophic larvae. By the spawning time, a large range of gamete sizes exists, but presumably only the larger gametes are released by repeated trickle spawning.

conservation status

Not listed by the IUCN.

significance to humans

Nothing known.

No common name

Comactinia echinoptera

order

Comatulida

family

Comasteridae

taxonomy

Comactinia echinoptera Müller, 1840, type locality unknown.

other common names

None known.

physical characteristics

Feather star with 10 arms, 1.9–6.5 in (30–165 mm) long, slightly broader in middle than at base, and with comb-bearing proximal pinnules. Arms most distal from mouth are less than half the length of those nearest to mouth. Has central anal cone and marginal mouth. Color is extremely variable, but arms have a reddish background color of varying shades and may present white, yellow, or brown spots. Pinnules are red to orange or yellow.

distribution

From southeastern Florida to Cabo Frio (and perhaps Alcatrazes Island), Brazil; through the Bahamas, Turks, and Caicos Islands, and the Antillean Arc, and Caribbean coasts of Central and South America. Intertidal to 295 ft (90 m), possibly to 590 ft (180 m).

habitat

Areas of current in shallow water, attached to hard substratum.

behavior

Occurs in high densities; nocturnal; extends the longest arms above the substratum, usually with central mass hidden, while attached in crevices.

feeding ecology and diet

Feeds through the vertical filtration fan posture.

reproductive biology

Nothing is known.

conservation status

Not listed by the IUCN.

significance to humans

None known.

Orange sea lily

Nemaster rubiginosa

order

Comatulida

family

Comasteridae

taxonomy

Nemaster rubiginosa Portalès, 1869, off Orange Key, Bahama Bank and off Tortugas.

other common names

None known.

physical characteristics

Feather star with 20 (up to 35) arms 3.9–7.9 in (100–200 mm) long, bright orange with a black stripe running along dorsal side. Mouth and anal cone about equal distance from center of tegmen.

distribution

Western Gulf of Mexico, southeastern Florida, Bahamas, Barbados; Caribbean coast of Central and South America from Belize to Bahia, Brazil. At 3.3–1,100 ft (1–334 m) deep.

habitat

Lives in shallow water, frequently sheltered from current, attached on hard substratum, favors the fore-edges of reef escarpments.

behavior

Central mass is hidden while attached to undersurfaces of hard substratum. Only arms are visible by day, but entire body may be exposed at night.

feeding ecology and diet

Feeds through the radial feeding posture.

reproductive biology

Produces gametes throughout the reproductive cycle (usually spring). By spawning time, a complete range of gamete development stages exists, from recently produced oocytes to fully mature ova.

conservation status

Not listed by the IUCN.

significance to humans

None known.

No common name

Tropiometra carinata

order

Comatulida

family

Tropiometridae

taxonomy

Tropiometra carianta Lamarck, 1816, Mauritius.

other common names

None known.

physical characteristics

Feather star with 10 arms, 3.9–7.1 in (100–180 mm) long. Arms and pinnules usually dark brown with yellow bands, although individuals may be yellow, yellow with brown bands, or orange.

distribution

Antillean Arc from Guadeloupe south; South America from Cartagena, Colombia, through Trinidad Tobago, to Santa Catarina, Brazil. Santa Helena. East Africa from Cape of Good Hope to Northern Somalia; Madagascar Islands from Comoros to the Seychelles, Mascarene Islands, and Cargados Carajos Shoals. Intertidal fringe to 276 ft (84 m).

habitat

Lives on current agitated shallow water, attached to hard substratum.

behavior

Specimens usually found in clumps, mainly of small individuals that tend to live near larger ones. Individuals may or may not have the central mass hidden while attached on lateral surfaces or in crevices or nooks (where more frequently found). No diel pattern of emergence.

feeding ecology and diet

Feeds through the vertical filtration fan posture.

reproductive biology

Free spawning in sea water and have lecititrophic larvae. Differs from other species because it spawns immature ova.

conservation status

Not listed by the IUCN.

significance to humans

None known.

Great West Indian sea lily

Cenocrinus asterius

order

Isocrinida

family

Isocrinidae

taxonomy

Cenocrinus asterius Linnaeus, 1775.

other common names

None known.

physical characteristics

Sea lily with up to 50 arms and a stalk, to 3.3 ft (1 m) long.

distribution

Northwest Providence Channel; Antillean Arc from Saba to Barbados, including Jamaica. At 600–1,920 ft (183–585 m) deep.

habitat

Groups of cirri along a curved stalk anchor individuals on hard substratum.

behavior

Individual arms wave rapidly up and down to prevent the settlement of other organisms or undesired particles on the crown. Can also move from place to place by crawling over substratum using their arms. Relocation may be stimulated by the presence of other individuals or other organisms as possible predators.

feeding ecology and diet

Feeds through the parabolic filtration fan posture.

reproductive biology

Nothing is known.

conservation status

Not listed by the IUCN.

significance to humans

None known.

West Atlantic stalked crinoid

Endoxocrinus parrae

order

Isocrinida

family

Isocrinidae

taxonomy

Endoxocrinus parrae Gervais, 1835, off Cuba.

other common names

None known.

physical characteristics

Sea lily similar to Cenocrinus asterius, but with a shorter stalk and a denser filtration fan. The arm-branching pattern is also different because its arms divide until there are a total of eight arms.

distribution

Off Cape Canaveral; Bahama Island; Antillean Arc; Yucatán Channel; off São Luiz, northeast Brazil. At 505–3,186 ft (154 to 971 m) deep, although some found in shallow water.

habitat

Groups of cirri along a curved stalk anchor the lily on hard substratum.

behavior

Individual arms wave rapidly up and down to prevent the settlement of other organisms or undesired particles on the crown. Can also move from place to place by crawling over substratum using their arms. Relocation may be stimulated by the presence of other individuals or other organisms as possible predators.

feeding ecology and diet

Feeds through the parabolic filtration fan posture.

reproductive biology

Nothing is known.

conservation status

Not listed by the IUCN.

significance to humans

None known.

Resources

Books

Ausich, William I. "Origin of Crinoids." In Echinoderm Research 1998, edited by Candia Carnevali and F. Bonasoro. Rotterdam: Balkema, 1999.

Hess, Hans, William I. Ausich, Carlton E. Brett, and Michel J. Simms, eds. Fossil Crinoids. Cambridge: Cambridge University Press, 1999.

Littlewood, D. Tim J., Andrew B. Smith, K. A. Clough, and Roland H. Emson. "Five Classes of Echinoderm and One School of Thought." In Echinoderms: San Francisco, edited by R. Mooi and M. Telford. Rotterdam: Balkema, 1998.

Simms, Mike J. "The Phylogeny of Post-Palaeozoic Crinoids." In Echinoderm Phylogeny and Evolutionary Biology, edited by C. R. C. Paul and A. B. Smith. Oxford: Clarendon Press, 1988.

Periodicals

Ameziane, Nadia, and Michel Roux. "Biodiversity and Historical Biogeography of Stalked Crinoids (Echinodermata) in the Deep Sea." Biodiversity and Conservation 6 (1997): 1557–1570.

Ausich, William I. "Early Phylogeny and Subclass Division of the Crinoidea (Phylum Echinodermata)." Journal of Paleontology 72 (1998): 499–510.

Ausich, William I., and Thomas W. Kammer. "The Study of Crinoids During the 20th Century and the Challenges of the 21st Century." Journal of Paleontology 75 (2001): 1161–1173.

Baumiller, Tomasz K., Michael LaBarbera, and Jeremy D. Woodley. "Ecology and Functional Morphology of the Isocrinid Cenocrinus asterius (Linnaeus) (Echinodermata: Crinoidea): In Situ and Laboratory Experiments and Observations." Bulletin of Marine Science 48 (1991): 731–748.

Fabricius, Katharina E. "Spatial Patterns in Shallow-Water Crinoid Communities on the Central Great Barrier Reef." Australian Journal of Marine and Freshwater Research 45 (1994): 1225–1236.

Guensburg, Thomas E., and James Sprinkle. "Earliest Crinoids: New Evidence for the Origin of the Dominant Paleozoic Echinoderms." Geology 29 (2001): 131–134.

Holland, Nicholas D., J. Rudi Strickler, and A. B. Leonard. "Particle Interception, Transport and Rejection by the Feather Star Oligometra serripina (Echinodermata: Crinoidea), Studied by Frame Analysis of Videotapes." Marine Biology 93 (1986): 111–126.

Lahaye, M. C., and Michel Jangoux. "Functional Morphology of the Podia and Ambulacral Grooves of the Comatulid Crinoid Antedon bifida (Echinodermata)." Marine Biology 86 (1985): 307–318.

MacCord, Fábio S., and Luiz F. Duarte, L. "Dispersion in Populations of Tropiometra carinata (Crinoidea: Comatulida) in the São Sebastião Channel, São Paulo State, Brazil." Estuarine Coastal and Shelf Science 54 (2002): 219–225.

Macurda, Jr., Donald B., and David L Meyer. "Feeding Posture of Modern Stalked Crinoids." Nature 247 (1974): 394–396.

McClintock, James B., Bill J. Baker, Tomasz K. Baumiller, and Charles G. Messing. "Lack of Chemical Defense in Two Species of Stalked Crinoids: Support for the Predation Hypothesis for Mesozoic Bathymetric Restriction." Journal of Experimental Marine Biology and Ecology 232 (1999): 1–7.

McEdward, Larry R., and Benjamin G. Miner. "Larval and Life-Cycle Pattern in Echinoderms." Canadian Journal of Zoology 79 (2001): 1125–1170.

Messing, Charles G., M. Christine RoseSmyth, Stuart R. Mailer, and John E. Miller. "Relocation Movement in a Stalked Crinoid (Echinodermata)." Bulletin of Marine Science 42 (1988): 480–487.

Meyer, David L. "Distribution and Living Habits of Comatulid Crinoids Near Discovery Bay, Jamaica." Bulletin of Marine Science 23 (1973): 244–259.

——. "Feeding Behavior and Ecology of Shallow-Water Unstalked Crinoids (Echinodermata) in the Caribbean Sea." Marine Biology 22 (1973): 105–129.

Meyer, David L., Charles G. Messing, and Donald B. Macurda, Jr. "Zoogeography of Tropical Western Atlantic Crinoidea (Echinodermata)." Bulletin of Marine Science 28 (1978): 412–441.

Nichols, David. "Evidence for a Sacrificial Response to Predation in the Reproductive Strategy of the Comatulid Crinoid Antedon bifida from the English Channel." Oceanologica Acta 19 (1996): 237–240.

——. "Reproductive Seasonality in the Comatulid Crinoid Antedon bifida (Pennant) from the English Channel." Philosophical Transactions of the Royal Society of London B 343 (1994): 113–134.

Vail, Lyle. "Diel Patterns of Emergence of Crinoids (Echinodermata) from Within a Reef at Lizard Island, Great Barrier Reef, Australia." Marine Biology 93 (1987): 551–560.

——. "Reproduction in Five Species of Crinoids at Lizard Island, Great Barrier Reef." Marine Biology 95 (1987): 431–446.

——. "Arm Growth and Regeneration in Oligometra serripina (Carpenter) (Echinodermata: Crinoidea) at Lizard Island, Great Barrier Reef." Journal of Experimental Marine Biology and Ecology 130 (1989): 189–204.

Young, Craig M., and Roland H. Emson. "Rapid Arm Movements in Stalked Crinoids." Biological Bulletin 188 (1995): 89–97.

Fábio Sá MacCord, MSc