Echinoidea

(Sea urchins and sand dollars)

Phylum Echinodermata

Class Echinoidea

Number of families 46

Thumbnail description
Ubiquitous, spine-covered animals that often live beneath the sand surface or hide out in rocky crevices and sea grass beds

Evolution and systematics

The class is divided into the subclass Perischoechinoidea, which has only one order and contains the most taxonomically primitive members of the class (e.g., pencil urchins), and the subclass Euechinoidea, which has 19 orders and contains the "true" echinoids. These are divided into two broad groups based on body shape: the regular urchins, which contain sea urchins, and the irregular urchins, which include both heart urchins and sand dollars. Collectively, there are 46 families and about 900 known species.

Echinoids are members of a much larger group of marine animals called echinoderms. These include asteroids (sea stars), ophiuroids (brittle stars), crinoids (feather stars), concentricycloids (sea daisies), and holothurians (sea cucumbers). The last group has the closest fossil linkage to echinoids than any other echinoderm class. The fossil record shows divergence from sea stars nearly 450 million years ago in the late Ordovician period, the oldest of these being the Perischoechinoidea. Regular and irregular urchins may have first evolved in the lower Jurassic, but these early forms remain poorly understood. In particular, the fossil genus Loriolella has an intermediate morphology, showing both irregular and regular characteristics. However, it is believed that during the Cretaceous period, sea level rise may have accounted for a dramatic increase in their diversity. Today, urchins play an important ecological role in many marine communities globally.

Physical characteristics

Echinoids come in a variety of different shapes, sizes, and color, but like all echinoderms, they have pentamerous radial symmetry (with the exception of irregular echinoids that have bilateral symmetry) and spiny skin. One of the smallest recorded urchins, Echinocyamus scaber, has a test diameter of only 0.2 in (0.5 cm), whereas the largest, Sperosoma giganteum, a deep-water species, has a test diameter up to 15 in (38 cm).

Echinoids have a hard calcareous shell made up of a skeleton of tightly packed or fused plates called a test. The skeleton is designed to prevent cracks from spreading if damaged. All urchins are covered with moveable spines that articulate like a ball and socket joint. However, their morphology is highly variable between species. Some range from the thick blunt spines of the pencil urchin, Eucidaris tribuloides, to the long poisonous spines of Diadema antillarum. Spines are primarily used for locomotion and defense against predators, although some species cover them with shell fragments, algae, or encrusting organisms to camouflage themselves from visual predators or, alternatively, to provide shade from direct sunlight.

The echinoid test has tiny pincer-like structures called pedicellariae that, in some species, are poisonous. These species tend to have fewer spines and use their pedicellariae in defense, while others use them to clear away settling microorganisms, unwanted parasites, and detritus. Sometimes they are visible to the naked eye, e.g., the stalked globular-shaped pedicellariae of the West Indian sea egg, Lytechinus variegatus.

As in other echinoderms, echinoids posses rows of tube feet that go from the very top of the anus down to the top of the mouth and they use them to trap food such as detritus and algae, assist in locomotion, prey capture, adhere to sub-strata and kelp stipes, and even respiration. On the dorsal (upper) surface of the test, a small sieve-like or perforated plate, madreportite, allows seawater into the water vascular system,

which is a canal of tubes running through the body to the tube feet. Following muscular contraction, seawater is drawn into the canal under pressure and directed at the tube feet, which then extend under its force. In most species, the anus is located on the dorsal surface. In some species the distinctive coloration of the anus is used by biologists and naturalist to identify differences between species. Diadema steosum, for example, has an orange ring around its anus, which is the only visible distinction from D. savignyi, which has an iridescent blue ring.

In regular urchins, the mouth is located on the aboral (opposite to the mouth) surface and consists of an array of very tough calcium carbonate plates embedded in tissue and five teeth arranged symmetrically. The entire feeding apparatus has a characteristic pattern has given rise to the name "Aristotle's lantern," a term used because of the resemblance to a five-sided Greek lantern and because urchins and sand dollars were a favorite animal of Aristotle. Some species such as the rock boring urchin, Echinostrephus aciculatus, use the teeth to rasp away at rock to form a cup-shaped hiding place. Urchins have a well-developed digestive system because they process a large amount of indigestible material such as sand, stones, and plant matter.

The test shape of regular urchins tends to be globular and pentaradiate, whereas that of irregular urchins tends to have a more flattened, oval, and bilateral symmetry. Their test shape generally reflects their mode of life. Irregular urchins, for example, are flattened for burrowing efficiently into sediment, and are covered in very short spines to aid feeding when beneath the seabed surface. Moreover, some species (e.g., sand dollar, Leodia sexiesperforata) have a series of slits or perforations called lunules. These may prevent it from being washed out of the sediment by the pressure of a passing wave surge. The internal organization of irregular urchins is generally similar to regular echinoids. The exception is that regular urchins have five pairs of gonads, whereas irregular urchins have between two and five.

Distribution

Echinoids live within the intertidal and subtidal waters of the Antarctic, Pacific, Atlantic, and Indian Oceans, although they are most abundant between 32.8 ft and 164 ft (10–50m). Deep-water species can inhabit depths below 16,400 ft (5,000 m). By contrast, some species such as the short-spined sea urchin, Anthocidaris crassispina, can survive being periodically exposed during deep wave surges or left behind in shallow rock pools at low tide.

Habitat

Regular sea urchins inhabit a broad range of environments from wave exposed rocky outcrops, crevices within rocks, rock pools, coral reefs, sandy lagoons to sea grass beds and kelp forests. The Antarctic species, Sterechinus neumayeri, has an energy-efficient metabolism that is physiologically adapted to freezing and food-deprived environments. Echinoids in warmer waters, where food is plentiful, have many predators and attempts to elude them involve highly evolved cryptic coloration to blending in with the background. The pencil-like spines of the pencil urchin, Eucidaris, for example, encourage encrusting algae to settle, making it virtually invisible during the day. This is not the case in the Galápagos Islands, where spines are not covered with epipthytes or epizotes, and the Eucidaris are completely exposed. Urchins inhabiting sea grass beds adopt a slightly different avoidance strategy; for example, some species cover their test with shell fragments, algae, and other types of debris to provide appropriate camouflage.

Heart urchins and sand dollars have a different mode of existence to sea urchins. Their flattened test is perfectly suited to life beneath the sediment surface. This instantly provides cover from visually orientated predators. Most species occupy sandy habitats and avoid muddy or silt-dominated sediments. Others such as the purple-heart urchin Spatangus purpureus prefer coarse gravel habitats.

Behavior

Most urchins are nocturnal foragers, although some locomotory activity can coincide with tidal changing if they occur during the day. Generally, these are small movements to compensate for change in seawater level associated with an outgoing or incoming tide. On wave-exposed shores, urchins can aggregate together to interlock spines, thus reducing the risk of being dislodged by a strong wave surge. Other aggregation patterns occur in defensive moves directed at predators, whereas other patterns usually signify feeding aggregations.

Sand dollars burrow into the sediment by moving at an angle to the surface, and heart urchins burrow by excavating allowing the animal to sink vertically into the sediment. Forward movement is then achieved by using its powerful laterally orientated spines.

Feeding ecology and diet

Sea urchins feed in a variety of different ways. Regular urchins use their teeth to bite and rasp encrusting algae, sea grasses, and seaweeds (herbivores), while others feed on sessile organisms, carrion, and detritus (ominvores). Foraging for food usually occurs at night to avoid predators. Most sea urchins are slow moving.

Echinoids are formidable grazers and are capable of significantly altering the marine community in which they live. Following a mass mortality of sea urchins (often caused by a parasitic disease), there is a rapid growth in algae that can have devastating impacts to coral reefs. In many shallow marine communities, such species are recognized as keystone because their impact is disproportionately large. Little is known about deep-sea urchins other than they are believed to have similar feeding habitats to shallow-water species.

Irregular urchins are primarily deposit feeders, processing fine organic matter that settles on the seafloor. Heart urchins process sand in bulk to feed on organic particles trapped in sediment. Some species draw down surface detritus into their burrows, via a respiratory funnel, using their tube feet. Sand dollars, however, are more efficient as they sieve fine sediment particles while burrowing. Their spines are dense enough to prevent sand grains from falling through, yet fine enough to allow particles to drop out onto strings of mucus before being transported to the mouth. Typically, sand dollars feed on small diatoms and organic matter that accumulate in sand. Some species can become suspension feeders by lifting the test obliquely out of the sediment (e.g., Dendraster excentricus) to face the prevailing water currents. The tube feet of some sand dollars are specialized for deposit feeding, whereas some heart urchins have tube feet around the mouth specialized in picking up organic-rich detritus from sediment (selective deposit feeding).

Predators of echinoids include sea otters, sea stars, crabs, eels, lobsters, and fishes such as wrasses, wolffish, American plaice, butterflyfish, porcupine fish, and triggerfish. In coral habitats, the urchin, Diadema, is consumed by triggerfish, which blow jets of water at it in an attempt to turn the test upside down. American plaice feed exclusively on sand dollars, which in most cases only live for a few years. By contrast, heart urchins have fewer predators and can survive for up to 12 years. Some deep-sea echinoids have poisonous spines to defend against predators.

Reproductive biology

All echinoids have separate sexes, which cannot be distinguished by their external appearance. Only Antarctic urchins show a tendency to brood their young. The sexual dimorphism of these brooding heart urchins is generally easy to see. The "marsupial" is pronounced in females; present but not conspicuous in males. Generally, females are broadcast spawners, releasing millions of eggs into the water column to be fertilized by male sperm. Sea urchin gonads are connected to small openings in the body wall called gonopores, through which eggs and sperm are released. The resultant larvae undergo a multistage planktonic phase before settlement and metamorphosis. Most have a characteristic larvae development, passing through a free-swimming stage called echinopluteus. Larvae are bilaterally symmetric and show no signs of pentaradiate symmetry, a characteristic of sea urchins. Metamorphosis gives rise to an adult body form either before or after settling on the sea floor. The duration between planktonic development and settlement is species-and geographically dependent.

Very few echinoids are brooders. The heart urchin, Abatus cordatus, broods its young to increase survival in freezing temperatures and food-deprived environments. These species omit a planktonic stage (lecithotrophs), a strategy to produce a small number of offspring that are larger in size.

Unlike sea stars, urchins are less likely to regenerate, although they will grow lost spines, tube feet, and repair holes in test.

Conservation status

No echinoid is listed on the IUCN Red List of Threatened Species. However, Diadema is protected by the state of Florida.

Significance to humans

Some echinoids are commercially valuable. In the United States, for example, red sea urchin, Strongylocentrotus francis-canus, purple sea urchin, S. purpuratus, and green urchin, S. droebachiensis, are harvested for their roe. In Japan, urchin eggs and their reproductive organs are eaten as a delicacy. In European waters, overexploitation of Paracentrotus lividus has resulted in habitat destruction and decline in population numbers. In areas where predators of urchins have been over-fished, urchin numbers can explode, causing devastating impacts to the marine community. In the Caribbean, for example, urchins have been responsible for 90% of the bio-erosion of coral reefs. Ironically, their efficiency at consuming unwanted algae and detritus has made them popular animals for aquariums.

The sea urchin, Diadema, is perhaps the most well known for its long spines that easily puncture human skin, leaving deep and painful wounds. The spine tips easily break off under the skin and are almost impossible to remove.

Urchins' dried and empty tests are a familiar component of strandlines on beaches and provide a valuable commodity for souvenir hunters.

Species accounts

List of Species

Slate-pencil urchin

Eucidaris tribuloides

order

Cidariida

family

Cidaridae

taxonomy

Eucidaris tribuloides Lamarck, 1816.

other common names

English: Mine urchin, club urchin.

physical characteristics

Size can reach 3.1 in (8 cm) in diameter, but with spines up to 5.1 in (13 cm). Coloration variable, from brown, red-brown to sometimes mottled brown-red with grayish white spine. Spines vary in color because of the attachment of encrusting organisms, particularly algae such as coralline. Solid brown cylindrical spines attached to a globular test.

distribution

Commonly found in less than 165 ft (50 m) of water, although can occur to a depth of 2,265 ft (800 m). Inhabits the coastal waters of North Carolina to Brazil.

habitat

Hides among sea grass beds such as turtle grass and in rocky crevices amongst coral, under rocks, and coral rubble. Usually found in lagoon areas. Spine length related to habitat. In high wave-exposed areas, spines are usually short.

behavior

Forages for food at night. In coral reef habitats, spines used to defend against predators and as a mechanism to wedge itself in a crevice. In sea grass beds, it does not cover itself with algae and detritus as camouflage, as do other urchins. Instead, it allows encrusting organisms to settle and grow on spines; a very slow-moving urchin.

feeding ecology and diet

Omnivorous, feeding on algae and small invertebrates like sea squirts, sponges, bryozoans, algae, gastropods, and bivalves. Although E. tribuloides has not been shown to be destructive to corals, a close relative that shares similar feeding habits, E. galapagensis, is destructive.

reproductive biology

Sexual reproduction; eggs and sperm are shed into the water column where fertilized eggs develop into free-living and transparent larvae with reddish eyespots before metamorphosing into juveniles and settling on the seabed. Spawning period linked to day-length and lunar cycle, but actual event varies geographically.

conservation status

Not listed by the IUCN.

significance to humans

None known.

Magnificent urchin

Astropyga magnifica

order

Diadematida

family

Diadematidae

taxonomy

Astropyga magnifica Clark, 1934.

other common names

None known.

physical characteristics

The test diameter can reach 7.8 in (20 cm) with brilliant coloration of golden yellow and iridescent blue spots. Spines are long and banded with reddish brown and yellowish white. Areas of test are bare.

distribution

Tropical coastal waters of the western Atlantic to the northeast South America down to about 295 ft (90 m).

habitat

Sandy bottoms, shell sand, and limestone outcrops on coral reefs.

behavior

A fast-moving urchin owing to its ability to walk on its spines. Patchy distribution, but some are known to aggregate. When threatened by predator, it clumps its spines in a defense position. Similar biology to the sea urchin, Diadema antillarum. Species associated with a number of different types of commensal animals such as small fish and shrimps.

feeding ecology and diet

Grazer, feeding on algae and occasionally small invertebrates.

reproductive biology

Sexual reproduction. Sexes are separate. Eggs and sperm are shed into the water column, where they are fertilized and develop into free-living larvae.

conservation status

Not listed by the IUCN.

significance to humans

None known.

Long-spined sea urchin

Diadema savignyi

order

Diadematida

family

Diadematidae

taxonomy

Diadema savignyi Michelin, 1845.

other common names

English: Blue eye urchin, black long-spined urchin.

physical characteristics

Relatively flattened, but oval test that can reach 3.1 in (8 cm) in diameter. Distinctive long and slender black or while spines, which vary in length from 1.9–3.9 in (5–10 cm). Test and spines are fragile. It has a distinctive iridescent blue ring around anus. Often mistaken for D. steosum, which has an orange ring. Darker animals tend to exist in the open on sand, whereas paler colored animals live in crevices or in turbid waters.

distribution

A ubiquitous shallow water species found throughout the Indo-Pacific and South Pacific Oceans to a depth of 1,312 ft (400 m).

habitat

Usually found inhabiting sheltered areas of coral reefs on rocky substrata or sandy lagoons, but occasionally occur in sea grass beds.

behavior

An active animal that is highly responsive to changes in light intensity. Often the test color will change according to changes in light. High densities may provide protection against predators. A variety of commensals associated with urchins, living among the spines, ranging from small shrimps and mysids to juvenile fish.

feeding ecology and diet

Voracious grazer of algal turf. Following unexpected mass mortalities, growth of algae is usually rapid and detrimental to many coral reefs globally. Tend to hide during the day in rocky crevices, but forage for food at night. Has many predators, mostly fish, mollusks, and crustaceans.

reproductive biology

Sexual reproduction; depending on geographical location, known to aggregate during spawning. Release of eggs and sperm into the water column coincides with the lunar cycle usually between summer and early winter.

conservation status

Not listed by the IUCN.

significance to humans

Considered ecologically important to many coral reef ecosystems. Spines are poisonous and easily puncture human skin, often leaving infection.

Short-spined sea urchin

Anthocidaris crassispina

order

Echinida

family

Echinometridae

taxonomy

Anthocidaris crassispina Agassiz, 1863.

other common names

English: Far Eastern violet sea urchin, purple sea urchin, black urchin, decorator urchin.

physical characteristics

Size variable, but commonly occurring between 0.8 and 2 in (2–5 cm) in diameter. Have black to dark violet coloration, with short spines.

distribution

Commonly found inhabiting the lower intertidal and shallow subtidal areas throughout the coastal waters of southern China, where it is an important benthic grazer of many algae-dominated communities.

habitat

Rocky shores are their principle habitat, where they appear to be well adapted to living in crevices and rock pools, especially on wave-exposed shores. Geographical distribution is limited by saline conditions; urchin densities tend to be lower on the oceanic southern and eastern coasts of Asia. When found on sand, their spines are usually covered in algae and shell fragments to camouflage them from predators.

behavior

Foraging activities are predominately nocturnal, although movements during the day correlate with changes in seawater depth during the tidal cycle.

feeding ecology and diet

Grazer, feeding mainly on encrusting algae (e.g., Corallina, Sargassum, Colpomenia, and Ulva), although the diet broadly reflects their seasonal availability. During the summer months, when the availability of prey is generally low, the diet is dominated by Corallina. Occasionally, other small organisms are consumed, such as bivalves and crabs.

reproductive biology

Sexual reproduction; spawning usually occurs between July and September, depending on seawater temperature. Broadcast fertilized eggs into the water column. Larvae undergo planktonic stage before settling to the seafloor.

conservation status

Not listed by the IUCN.

significance to humans

Commercially harvested for roe in the coastal waters of Asia. Also used as an indicator species for toxic chemicals in the marine environment. The occurrence of an indicator species is usually associated with impacts from anthropogenic activity, such as high concentrations of chemicals released from outfalls, or industrial spill run off from the land into the sea.

Rock boring urchin

Echinostrephus aciculatus

order

Echinida

family

Echinometridae

taxonomy

Echinostrephus aciculatus Agassiz, 1863.

other common names

English: Needle-spined urchin, reef boring sea-hedgehog.

physical characteristics

Flattened and circular test up to 3.1 in (8 cm) in diameter. Has black to reddish purple coloration with rigid needle-like spines.

distribution

Indo-Pacific coastal waters to a depth of 165 ft (50 m).

habitat

Lives in rock and coral.

behavior

Bores into rock to create living-chamber. Uses spines on its upper surface as defense against predators. As they grow, individuals can become trapped in chamber.

feeding ecology and diet

Dependent on catching drifting algae that passes across mouth of burrow. Uses tube feet to capture algae.

reproductive biology

Sexual reproduction. Sexes are separate. Eggs and sperm are shed into the water column, where they are fertilized and develop into free-living larvae.

conservation status

Not listed by the IUCN.

significance to humans

None known.

Pea urchin

Echinocyamus pusillus

order

Laganina

family

Fibulariidae

taxonomy

Echinocyamus pusillus Muller, 1776.

other common names

English: Dwarf sea urchin.

physical characteristics

Among one of the smallest urchins, its tiny oval test measures up to a maximum 0.6 in (1.5 cm) in length. Usually gray-green to bright green in color with very short spines, which give the animal a velvet texture to touch.

distribution

European coastal waters to a depth of 165 ft (50 m).

habitat

Lives buried in coarse gravel, sandy sediment, and among Zosteria and maerl beds.

behavior

Little known.

feeding ecology and diet

Primarily deposit feeder, but also preys on foraminiferans and grazes on individual sediment grains for its organic coating.

reproductive biology

Sexual reproduction. Sexes are separate. Eggs and sperm are shed into the water column, where they are fertilized and develop into free-living larvae.

conservation status

Not listed by the IUCN.

significance to humans

None known.

Western sand dollar

Dendraster excentricus

order

Scutellina

family

Dendrasteridae

taxonomy

Dendraster excentricus Eschscholtz, 1831.

other common names

English: Eccentric sand dollar.

physical characteristics

Rigid test measuring up to 3.5 in (9 cm) and covered with moveable spines. Pale gray-lavender to dark purplish black coloration; characteristic pentaradiate or petal-shaped pattern tube feet on upper surface of test.

distribution

Northeastern coasts of the Pacific ocean from southern Alaska to Mexico. Found in depths between 130–295 ft (40–90 m).

habitat

Inhabits sandy bottoms within sheltered bays, lagoons, and open coastal areas. Commonly found in dense aggregations forming a carpet of animals.

behavior

Occurs in large numbers on the seabed. These high densities are thought to help influence the nature of near-bed currents to assist in feeding.

feeding ecology and diet

The only echinoid to suspension feed, trapping suspended organic particles as they drift in passing water currents. Mucus strands assist in trapping organic matter. Juveniles ingest sand when feeding to act as ballast. Stand in the sand obliquely when feeding and use their tube feet for respiration and catching food.

reproductive biology

Sexual reproduction; spawning period between July and August. Adults may feed on larvae, but not their eggs because of a protective coating. Settling larvae have a greater protection from predators if they settle within existing sand dollar beds. Estimated lifespan is up to 15 years.

conservation status

Not listed by the IUCN.

significance to humans

Selected by beachcombers for their aesthetic value.

Six keyhole sand dollar

Leodia sexiesperforata

order

Scutellina

family

Mellitidae

taxonomy

Leodia sexiesperforata Leske, 1778.

other common names

English: Sand dollar.

physical characteristics

Thin and flattened disc with six characteristic slot-like holes and distinctive pentaradiate or petal-like pattern tube feet on upper surface. Diameter is up to 3.9 in (10 cm). Yellow to light brown in color.

distribution

Occurs along coastal waters of the western Atlantic from North Carolina to Uruguay. Subtidally to a depth of 200 ft (60 m).

habitat

Commonly found inhabiting open sandy areas clear of algae.

behavior

Burrows vertically into sand to several inches (centimeters) below surface. Species is host to the crab, Dissodactylus crinitichelis.

feeding ecology and diet

Feeds on organic particles such as algae and detritus. Uses mucus strands to collected food. Known predators include the triggerfish (Balistes capriscus) and helmet conch (Cassis tuberosa).

reproductive biology

Sexual reproduction; spawning tends to occur during rainy season between late summer and autumn.

conservation status

Not listed by the IUCN.

significance to humans

Collected by beachcombers for their aesthetic value.

Sea biscuit

Plagiobrissus grandis

order

Spatangida

family

Brissidae

taxonomy

Plagiobrissus grandis Gmelin, 1788.

other common names

English: Heart urchin, long-spined sea biscuit, great red-footed urchin.

physical characteristics

One of the largest irregular urchins; longest dimension is their oval-shaped test that can reach 9.8 in (25 cm) in length. Colors vary from yellow or tan to reddish brown. Test covered with medium-sized spines, although some on the upper surface are up to 3.9 in (10 cm) long. Flat underneath with five rows of tube feet in ambulacral groove.

distribution

Found in shallow waters from Florida to the West Indies and Brazil. Common at depths less than 164 ft (50 m), but can occur in depths greater than 655 ft (200 m).

habitat

Inhabits sandy coastal lagoons.

behavior

Burrows into the sediment. Its long spines are used to defend itself from predators when buried. Often associated with the commensal crab, Dissodactylus primitivus.

feeding ecology and diet

Deposit feeder; feeding is suspected to occur both night and day. Main predators are the large helmet conchs, Cassis tuberosa and C. madagascariensis spinella.

reproductive biology

Sexual reproduction. Sexes are separate. Eggs and sperm are released into the water column, where they are fertilized and develop into free-living larvae.

conservation status

Not listed by the IUCN.

significance to humans

Known to have poisonous spines.

Heart urchin

Abatus cordatus

order

Spatangida

family

Schizasteridae

taxonomy

Abatus cordatus Verrill, 1876.

other common names

None known.

physical characteristics

Diameter can reach 2.3 in (6 cm). Coloration usually brownish yellow. Oval shaped with dense coat of fine spines that keep sediment clear of test during burrowing activity.

distribution

Limited distribution. Endemic to the Kerguelen Islands, Antarctica.

habitat

Inhabits shallow inlets and bays, living buried in fine sand usually protected from wave swell.

behavior

Little known, but lives within dense populations.

feeding ecology and diet

Little known but other species belonging to the genus Abatus are deposit feeders, usually gathering detritus with their tube feet.

reproductive biology

Females brood their young in dorsal pouch. The strategy is to produce few eggs and small amounts of sperm at any one time. The advantage is a higher survival rate of offspring compared to the more usual strategy of broadcasting species.

conservation status

Not listed by the IUCN.

significance to humans

None known.

Tuxedo pincushion urchin

Mespilia globulus

order

Temnopleurida

family

Temnopleuridae

taxonomy

Mespilia globules Linnaeus, 1758.

other common names

English: Royal urchin, sphere urchin, globular sea urchin, ball sea-hedgehog.

physical characteristics

Test can reach 2.3 in (6 cm) in diameter and has five to 10 broad bands of bright blue coloration with bands of reddish-brown spines, which give it a very striking appearance.

distribution

Coastal waters of China, Japan, Indian Ocean, and the Philippines.

habitat

During the day will hide among rocks, rubble, and in crevices associated with coral reefs.

behavior

Solitary animal. Camouflages test with shell fragments and algae held on with fine cilia hairs between spines.

feeding ecology and diet

Herbivore, feeding on micro-algae and encrusting coralline. Forages for food at night.

reproductive biology

Sexual reproduction.

conservation status

Not listed by the IUCN.

significance to humans

Used in home aquaria.

West Indian sea egg

Lytechinus variegatus

order

Temnopleurida

family

Toxopneustidae

taxonomy

Lytechinus variegates Lamarck, 1816.

other common names

English: Short-spined urchin.

physical characteristics

Large, up to 3.9 in (10 cm) in diameter with spherical test that appears greenish with green-purple spines. Stalked pedicellariae are white or pink and visible to the naked eye.

distribution

Found in coastal lagoons from the southwestern Atlantic to the Caribbean and Brazil. Subtidal to a depth of 1,090 ft (250 m).

habitat

Found inhabiting sea grass beds (Thalassia), sandy bottoms, and among rocks. Avoids turbid waters containing high concentrations of suspended silts.

behavior

Covers its test with shell fragments, rubble, grass blades, and algae for camouflage or protection against strong sunlight.

feeding ecology and diet

Herbivore, feeding on turtle grass (Thalassia). Predators include reef fish, helmet conch (Cassis tuberosa), and shore birds.

reproductive biology

Sexual reproduction; spawning season between spring and summer and occurs within the lunar cycle. Metamorphosis of settling young tends to occur in the intertidal regions.

conservation status

Not listed by the IUCN.

significance to humans

Roe may be consumed locally.

Resources

Books

Anzalone, L. "Loriolella, and the Transition from Regular to Irregular Echinoids." In Echinoderm Research, Proceedings of the 5th European Conference on Echinoderms, edited by Maria D. C. Carnevali and Francesco Bonasoro. Rotterdam: A. A. Balkema, 1999.

Birkeland, C. "The Influence of Echinoderms on Coral-reef Communities." In Echinoderm Studies, edited by Michael Jangoux and John Lawrence. Rotterdam: A. A. Balkema, 1989.

Ebert, T. A. "Recruitment in Echinoderms." In Echinoderm Studies, edited by Michael Jangoux and John Lawrence. Rotterdam: A. A. Balkema, 1983.

Eugene, N. K. Marine Invertebrates of the Pacific Northwest. Seattle: University of Washington Press, 1996.

Hendler, G., J. E. Miller, D. L. Pawson, and P. M. Kier. Sea Stars, Sea Urchins, and Allies: Echinoderms of Florida and the Caribbean. Washington, DC, and London: The Smithsonian Institution Press, 1995.

Kozloff, E. N. Seashore Life of the Northern Pacific Coast. Seattle: University of Washington Press, 1993.

Lawrence, J. A Functional Biology of Echinoderms. London and Sydney: Croom Helm Press, 1987.

Lerman, M. Marine Biology: Environment, Diversity, and Ecology. San Francisco: Cummings Publishing Company, 1986.

Littlewood, D. T. J. "Echinoderm Class Relationships Revisited." In Echinoderm Research, edited by H. Roland, A. Emson, B. Smith, and A. C. Campbell. Rotterdam: A. A. Balkema, 1995.

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Other

"Classification of the Extant Echinodermata." [July 15, 2003]. <http://www.calacademy.org/research/izg/echinoderm/classify.htm>.

Steven Mark Freeman, PhD