The starlet sea anemone (''Nematostella vectensis'') is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...

of small

sea anemone Sea anemones are a group of predatory marine invertebrates of the order Actiniaria. Because of their colourful appearance, they are named after the '' Anemone'', a terrestrial flowering plant. Sea anemones are classified in the phylum Cnidaria, ...

in the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Edwardsiidae Edwardsiidae is a family of sea anemones. Edwardsiids have long thin bodies and live buried in sediments or in holes or crevices in rock. Genera The following genera are recognized within the family Edwardsiidae. * '' Drillactis'' Verrill, 1922 ...

native to the east coast of the United States, with introduced populations along the coast of southeast

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe ...

and the west coast of the United States (class ''Anthozoa'', phylum ''Cnidaria'', a sister group of

Bilateria The Bilateria or bilaterians are animals with bilateral symmetry as an embryo, i.e. having a left and a right side that are mirror images of each other. This also means they have a head and a tail (anterior-posterior axis) as well as a belly and ...

). Populations have also been located in Nova Scotia, Canada. This sea anemone is found in the shallow brackish water of coastal lagoons and

salt marsh A salt marsh or saltmarsh, also known as a coastal salt marsh or a tidal marsh, is a coastal ecosystem in the upper coastal intertidal zone between land and open saltwater or brackish water that is regularly flooded by the tides. It is domin ...

es where its slender column is usually buried in the mud and its tentacles exposed. Its

genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ...

has been sequenced and it is cultivated in the laboratory as a

model organism A model organism (often shortened to model) is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the model organism will provide insight into the workin ...

, but the

IUCN The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...

has listed it as being a "

Vulnerable species A vulnerable species is a species which has been categorized by the International Union for Conservation of Nature as being threatened with extinction unless the circumstances that are threatening its survival and reproduction improve. Vulnera ...

" in the wild.

Description

The starlet sea anemone has a bulbous basal end and a contracting column that ranges in length from less than . There is a fairly distinct division between the scapus, the main part of the column, and the capitulum, the part just below the crown of

tentacle In zoology, a tentacle is a flexible, mobile, and elongated organ present in some species of animals, most of them invertebrates. In animal anatomy, tentacles usually occur in one or more pairs. Anatomically, the tentacles of animals work main ...

s. The outer surface of the column has a loose covering of mucus to which particles of sediment tend to adhere. At the top of the column is an oral disk containing the mouth surrounded by two rings of long slender tentacles. Typically there are fourteen but sometimes as many as twenty tentacles, the outermost being longer than the inner whorl. The starlet sea anemone is translucent and largely colourless but usually has a pattern of white markings on the column and white banding on the tentacles.

Distribution and habitat

The starlet sea anemone occurs on the eastern and westward seaboard of North America. Its range extends from Nova Scotia to Louisiana on the east coast and from Washington to California on the west coast. It is also known from three locations in the United Kingdom—two in

East Anglia East Anglia is an area in the East of England, often defined as including the counties of Norfolk, Suffolk and Cambridgeshire. The name derives from the Anglo-Saxon kingdom of the East Angles, a people whose name originated in Anglia, in ...

and one on the

Isle of Wight The Isle of Wight ( ) is a county in the English Channel, off the coast of Hampshire, from which it is separated by the Solent. It is the largest and second-most populous island of England. Referred to as 'The Island' by residents, the Is ...

. Its typical habitat is

brackish Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estua ...

ponds, brackish lagoons and ditches and pools in

es. It is found in positions with little water flow and seldom occurs more than one metre (yard) below the surface. It can tolerate a wide range of salinities, 2 to 52 parts per thousand in southern England, and seems to breed best at around 11 parts per thousand. It is typically buried up to the crown in fine silt or sand, with its tentacles flared out on the surface of the sediment. When not feeding, the tentacles are retracted into the column.

Ecology

The starlet sea anemone sometimes occurs at high densities (as many as 2,700 per square metre has been recorded). Other

megafauna In terrestrial zoology, the megafauna (from Greek μέγας ''megas'' "large" and New Latin ''fauna'' "animal life") comprises the large or giant animals of an area, habitat, or geological period, extinct and/or extant. The most common thresho ...

found alongside it in England include the lagoon cockle ('' Cerastoderma glaucum''), the lagoon sandworm '' Armandia cirrhosa'', the

isopod Isopoda is an order of crustaceans that includes woodlice and their relatives. Isopods live in the sea, in fresh water, or on land. All have rigid, segmented exoskeletons, two pairs of antennae, seven pairs of jointed limbs on the thorax, and ...

'' Idotea chelipes'' and the

amphipod Amphipoda is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods range in size from and are mostly detritivores or scavengers. There are more than 9,900 amphipod species so far descri ...

s '' Monocorophium insidiosum'' and '' Gammarus insensibilis''. Plants in its habitat include

foxtail stonewort Foxtail or fox tail may refer to: Plants * Foxtail (diaspore), the dry spikelet or spikelet cluster of some grasses ** '' Alopecurus'', foxtail grasses - the scientific name literally means "fox tail" ** '' Bromus madritensis'', foxtail brome ** ...

, ''Lamprothamniun papulosum'', green algae '' Chaetomorpha'' spp., and ditch grass ('' Ruppia'') spp. In North America it is found among the saltmarsh grasses ''

Spartina patens ''Sporobolus pumilus'', the saltmeadow cordgrass, also known as salt hay, is a species of cordgrass native to the Atlantic coast of the Americas, from Newfoundland south along the eastern United States to the Caribbean and north-eastern Mexico. ...

'' and '' Spartina alterniflora'' and the green algae ''Chaetomorpha'' spp. and '' Cladophora''. The starlet sea anemone feeds on

ostracod Ostracods, or ostracodes, are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 70,000 species (only 13,000 of which are extant) have been identified, grouped into several orders. They are small crustaceans, typic ...

copepod Copepods (; meaning "oar-feet") are a group of small crustaceans found in nearly every freshwater and saltwater habitat. Some species are planktonic (inhabiting sea waters), some are benthic (living on the ocean floor), a number of species have ...

s, small

mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is est ...

chironomid The Chironomidae (informally known as chironomids, nonbiting midges, or lake flies) comprise a family of nematoceran flies with a global distribution. They are closely related to the Ceratopogonidae, Simuliidae, and Thaumaleidae. Many specie ...

larvae,

nematode The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant- parasitic nematodes also known as eelworms. They are a diverse animal phylum inhabiting a bro ...

polychaete Polychaeta () is a paraphyletic class of generally marine annelid worms, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are made ...

s, small

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapoda, decapods, ostracoda, seed shrimp, branchiopoda, branchiopods, argulidae, fish lice, krill, remipedes, isopoda, isopods, barnacles, copepods, ...

s and egg masses. The only known

predator Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill t ...

of this sea anemone is the grass shrimp ''

Palaemonetes pugio ''Palaemonetes pugio'' (daggerblade grass shrimp) is a small, transparent shrimp with yellow coloring and brownish spots. It can be found in estuarine and tidal marsh habitats throughout the western Atlantic Ocean and Gulf of Mexico. ''Palaemon ...

''.

Life cycle

On the east coast of the United States, reproduction is mostly by sexual means. The anemones become mature at about three to four months with a column length of or more. Up to two thousand eggs are laid in a gelatinous clump. The spherical

planula A planula is the free-swimming, flattened, ciliated, bilaterally symmetric larval form of various cnidarian species and also in some species of Ctenophores. Some groups of Nemerteans also produce larvae that are very similar to the planula, which ...

larvae that hatch about two days later spend around a week in the

water column A water column is a conceptual column of water from the surface of a sea, river or lake to the bottom sediment.Munson, B.H., Axler, R., Hagley C., Host G., Merrick G., Richards C. (2004).Glossary. ''Water on the Web''. University of Minnesota-D ...

before settling on the sediment and undergoing

metamorphosis Metamorphosis is a biological process by which an animal physically develops including birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation. Some inse ...

into juveniles. In southern England all individuals seem to be female and reproduction is by

budding Budding or blastogenesis is a type of asexual reproduction in which a new organism develops from an outgrowth or bud due to cell division at one particular site. For example, the small bulb-like projection coming out from the yeast cell is kno ...

. Two-crowned anemones are common in this location and these individuals later undergo fission into separate sea anemones. On the west coast of the United States, all individuals are also female while in Nova Scotia, all are male, and reproduction in both these populations is likely to be by asexual means.

Research

Cnidarians are the simplest animals in which the cells are organized into tissues. Specialist cells include

epithelial cells Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellu ...

neuron A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa ...

muscle fibres A muscle cell is also known as a myocyte when referring to either a cardiac muscle cell (cardiomyocyte), or a smooth muscle cell as these are both small cells. A skeletal muscle cell is long and threadlike with many nuclei and is called a musc ...

and

stem cell In multicellular organisms, stem cells are undifferentiated or partially differentiated cells that can differentiate into various types of cells and proliferate indefinitely to produce more of the same stem cell. They are the earliest type of ...

s, and there is a complex

extracellular matrix In biology, the extracellular matrix (ECM), also called intercellular matrix, is a three-dimensional network consisting of extracellular macromolecules and minerals, such as collagen, enzymes, glycoproteins and hydroxyapatite that provide s ...

. ''Nematostella vectensis'' is used as a

for the study of

evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...

genomics Genomics is an interdisciplinary field of biology focusing on the structure, function, evolution, mapping, and editing of genomes. A genome is an organism's complete set of DNA, including all of its genes as well as its hierarchical, three-dim ...

, reproductive biology,

developmental biology Developmental biology is the study of the process by which animals and plants grow and develop. Developmental biology also encompasses the biology of regeneration, asexual reproduction, metamorphosis, and the growth and differentiation of st ...

and

ecology Ecology () is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere level. Ecology overl ...

. It is easy to care for in the laboratory, even in inland locations, and a

protocol Protocol may refer to: Sociology and politics * Protocol (politics), a formal agreement between nation states * Protocol (diplomacy), the etiquette of diplomacy and affairs of state * Etiquette, a code of personal behavior Science and technology ...

has been developed for the induction of

gametogenesis Gametogenesis is a biological process by which diploid or haploid precursor cells undergo cell division and differentiation to form mature haploid gametes. Depending on the biological life cycle of the organism, gametogenesis occurs by meiotic di ...

which can yield large numbers of embryos on a daily basis. Its

has been sequenced. Analysis of expressed sequence tags and the whole genome have shown a remarkable degree of similarity in the gene sequence conservation and complexity between the sea anemone and vertebrates. Recent sequencing of its complex genome has shown that it has an estimated complement of 18,000 protein-coding genes. Its repertoire, structure, and organization is very conserved when compared with that of vertebrates but surprisingly different from that of fruit flies and nematodes, which have lost many genes and introns and have experienced genome rearrangements, indicating the genome of their common ancestor also was a complex genome Researchers at the

Sars International Centre for Marine Molecular Biology The Sars International Centre for Marine Molecular Biology is a research establishment located at Bergen in Norway. History Sars International Centre for Marine Molecular Biology was established in April 1997. It is located at the Bergen High Tech ...

have found that genes concerned in the formation of the head in higher animals are also present in ''Nematostella vectensis''. The larva swims with the end with its main sense organ in front, and at metamorphosis this end becomes the lower end of the column. The "head" gene is concerned in the development of this lower end rather than the oral crown and tentacles.

References

External links

StellaBase

''Nematostella''.
Tree of Life.