Crinoidea (Sea Lilies and Feather Stars)

(invertebrate zoology) A class of radially symmetrical crinozoans in which the adult body is flower-shaped and is either carried on an anchored stem or is free-living.

(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

Resources

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.

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.

[Article by: Fábio Sá MacCord, MSc]

A class of exclusively suspension-feeding echinoderms with long, slender arms arranged radially around the calyx, a rigid cuplike structure composed of calcareous plates. The radial arm arrangement gives crinoids a flowerlike appearance (see illustration). Two basic adult body types are recognized: the sea lilies, with a long, anchored stem vertically supporting the calyx and arms above the sea bottom; and the stemless featherstars, or comatulids, with a whorl of flexible appendages on the calyx. Crinoids have a worldwide distribution and can be found in all seas except the Black and Baltic. They occupy depths ranging from just below sea level to a depth of over 9000 m (29,500 ft). Sea lilies are found only at depths greater than 100 m (330 ft), whereas comatulids are most abundant and diverse in shallow, tropical coral reef environments. See also Blastoidea; Pelmatozoa.

Schematic diagram of a stemmed crinoid in feeding posture.

Over 500 species of living comatulids have been described, and many of these can be extremely abundant locally, yet fewer than 100 species of living sea lilies are known. These patterns contrast starkly with the fossil record of crinoids, which is dominated by stemmed crinoids: of the more than 5000 described fossil species, more than 90% have stems.

Living crinoids have no economic importance and are not used for food by humans. However, their fossil remains are often the dominant constituent of building limestone (for example, Indiana limestone) which is highly valued.

Adult crinoids range in size from a few centimeters for some of the stemless forms to several meters from base of the stem to tip of the arms for the largest stemmed crinoids. They also vary in color from the largely bland whites and grays of the deep-water forms to the brilliant reds, yellows, and purples of the shallow-water tropical featherstars. In spite of the size range, color differences, and stemmed or stemless condition as adults, all crinoids share a suite of morphological traits that can be traced back to the Ordovician age, nearly 500 million years ago. See also Ordovician.

Crinoids are exclusively passive suspension feeders, extracting food particles from the ambient water. Crinoids are indiscriminate feeders, and the tube feet capture organic and inorganic particles with a median size of about 50 micrometers and rarely larger than 500 μm. The organic food component consists primarily of phytoplankton, protozoa, and crustacea. Crinoid morphology and behavior strongly reflect their total reliance on water movement for nutrient supply. Crinoids avoid slack-water environments, living in areas dominated by currents, wave action, or multidirectional flows.

Crinoids have a long and rich fossil record, and at times in Earth history they were numerically one of the dominant members of the benthic marine ecosystem. The first undisputed crinoids were found in rocks of the Ordovician Period. The Mississippian Period, known as the Age of Crinoids, represents the peak in their abundance and diversity. Crinoids remained an important component of marine communities until the Permo-Triassic extinction event that signaled the end of the Paleozoic Era. This event led to a great reduction in crinoid diversity. A single genus, Holocrinus, found in Lower Triassic rocks, is the most primitive member of the Articulata, a subclass that includes all post-Paleozoic crinoids. See also Articulata (Echinodermata); Crinozoa; Echinodermata.