''Platynereis dumerilii'' is a species of

annelid The annelids (Annelida , from Latin ', "little ring"), also known as the segmented worms, are a large phylum, with over 22,000 extant species including ragworms, earthworms, and leeches. The species exist in and have adapted to various ecol ...

polychaete Polychaeta () is a paraphyletic class (biology), class of generally marine invertebrate, marine annelid worms, common name, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that ...

worm. It was originally placed into the genus ''

Nereis ''Nereis'' is a genus of polychaete worms in the family Nereididae. It comprises many species, most of which are marine. ''Nereis'' possess setae and parapodia for locomotion and gas exchange. They may have two types of setae, which are found on ...

'' and later reassigned to the genus ''

Platynereis ''Platynereis'' is a genus of marine biology, marine annelid worms that belongs to the Nereididae, a family of errant polychaete worms. The species ''Platynereis dumerilii'' is used in development biology to study development (embryogenesis), in ...

''. ''Platynereis dumerilii'' lives in coastal marine waters from temperate to tropical zones. It can be found in a wide range from the

Azores ) , motto =( en, "Rather die free than subjected in peace") , anthem= ( en, "Anthem of the Azores") , image_map=Locator_map_of_Azores_in_EU.svg , map_alt=Location of the Azores within the European Union , map_caption=Location of the Azores wi ...

, the

Mediterranean The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the e ...

, in the

North Sea The North Sea lies between Great Britain, Norway, Denmark, Germany, the Netherlands and Belgium. An epeiric sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian S ...

, the

English Channel The English Channel, "The Sleeve"; nrf, la Maunche, "The Sleeve" (Cotentinais) or ( Jèrriais), (Guernésiais), "The Channel"; br, Mor Breizh, "Sea of Brittany"; cy, Môr Udd, "Lord's Sea"; kw, Mor Bretannek, "British Sea"; nl, Het Kana ...

, and the

Atlantic The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe an ...

down to the

Cape of Good Hope The Cape of Good Hope ( af, Kaap die Goeie Hoop ) ;''Kaap'' in isolation: pt, Cabo da Boa Esperança is a rocky headland on the Atlantic coast of the Cape Peninsula in South Africa. A common misconception is that the Cape of Good Hope is t ...

, in the

Black Sea The Black Sea is a marginal mediterranean sea of the Atlantic Ocean lying between Europe and Asia, east of the Balkans, south of the East European Plain, west of the Caucasus, and north of Anatolia. It is bounded by Bulgaria, Georgia, Roma ...

, the

Red Sea The Red Sea ( ar, البحر الأحمر - بحر القلزم, translit=Modern: al-Baḥr al-ʾAḥmar, Medieval: Baḥr al-Qulzum; or ; Coptic: ⲫⲓⲟⲙ ⲛ̀ϩⲁϩ ''Phiom Enhah'' or ⲫⲓⲟⲙ ⲛ̀ϣⲁⲣⲓ ''Phiom ǹšari''; T ...

, the

Persian Gulf The Persian Gulf ( fa, خلیج فارس, translit=xalij-e fârs, lit=Gulf of Persis, Fars, ), sometimes called the ( ar, اَلْخَلِيْجُ ٱلْعَرَبِيُّ, Al-Khalīj al-ˁArabī), is a Mediterranean sea (oceanography), me ...

, the

Sea of Japan The Sea of Japan is the marginal sea between the Japanese archipelago, Sakhalin, the Korean Peninsula, and the mainland of the Russian Far East. The Japanese archipelago separates the sea from the Pacific Ocean. Like the Mediterranean Sea, it h ...

, the

Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...

, and the

Kerguelen Islands The Kerguelen Islands ( or ; in French commonly ' but officially ', ), also known as the Desolation Islands (' in French), are a group of islands in the sub-Antarctic constituting one of the two exposed parts of the Kerguelen Plateau, a large ...

. ''Platynereis dumerilii'' is today an important lab animal, it is considered as a

living fossil A living fossil is an extant taxon that cosmetically resembles related species known only from the fossil record. To be considered a living fossil, the fossil species must be old relative to the time of origin of the extant clade. Living fossi ...

, and it is used in many

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

studies as a model organism.

Description

''Platynereis dumerilii'' is a small marine

ragworm Nereididae (formerly spelled Nereidae) are a family of polychaete worms. It contains about 500 – mostly marine – species grouped into 42 genera. They may be commonly called ragworms or clam worms. Characteristics The prostomium of ...

: Males reach a length of 2 to 3 cm, while females reach a length of 3 to 4 cm. Like a number of invertebrate phyla, ''Platynereis dumerilii'' has an axochord, a paired longitudinal muscle that displays striking similarities to the

notochord In anatomy, the notochord is a flexible rod which is similar in structure to the stiffer cartilage. If a species has a notochord at any stage of its life cycle (along with 4 other features), it is, by definition, a chordate. The notochord consis ...

regarding position, developmental origin, and expression profile. Its early

trochophore A trochophore (; also spelled trocophore) is a type of free-swimming planktonic marine larva with several bands of cilia. By moving their cilia rapidly, they make a water eddy, to control their movement, and to bring their food closer, to captur ...

larva has a pair of the simplest eyes in the animal kingdom, each eye consists only of a

photoreceptor cell A photoreceptor cell is a specialized type of neuroepithelial cell found in the retina that is capable of visual phototransduction. The great biological importance of photoreceptors is that they convert light (visible electromagnetic radiatio ...

and a pigment cell.

Locomotion

''P. dumerilii'' worms have a

ciliated The cilium, plural cilia (), is a membrane-bound organelle found on most types of eukaryotic cell, and certain microorganisms known as ciliates. Cilia are absent in bacteria and archaea. The cilium has the shape of a slender threadlike projecti ...

surface which beats synchronously to drive locomotion and fluid flow. Larvae have segmental multiciliated cells that regularly display spontaneous coordinated ciliary arrests, which compose the ciliomotor circuitry in the worms. Whole-body coordination of ciliary locomotion is performed by a "stop-and-go pacemaker system". As the worms develop, they use

chaeta A chaeta or cheta (from Greek χαίτη “crest, mane, flowing hair"; plural: chaetae) is a chitinous bristle or seta found in annelid worms, (although the term is also frequently used to describe similar structures in other invertebrates suc ...

e, and then

parapodia In invertebrates, the term parapodium ( Gr. ''para'', beyond or beside + ''podia'', feet; plural: parapodia) refers to lateral outgrowths or protrusions from the body. Parapodia are predominantly found in annelids, where they are paired, unjointed ...

, for locomotion. Unlike other polychaetes, in ''Platynereis'' larvae, the parapodia are used only for navigation while the cilia are responsible for propulsive force.

Senses

Photoreceptor cells

''Platynereis dumerilii'' larvae possess two kinds of

Rhabdom The compound eyes of arthropods like insects, crustaceans and millipedes are composed of units called ommatidia (singular: ommatidium). An ommatidium contains a cluster of photoreceptor cells surrounded by support cells and pigment cells. The ou ...

eric and ciliary photoreceptor cells. The ciliary photoreceptor cells are located in the deep brain of the larva. They are not shaded by

pigment A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compo ...

and thus perceive non-directional light. The ciliary photoreceptor cells resemble molecularly and morphologically the rods and

cones A cone is a three-dimensional geometric shape that tapers smoothly from a flat base (frequently, though not necessarily, circular) to a point called the apex or vertex. A cone is formed by a set of line segments, half-lines, or lines conn ...

of the human

eye Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and conv ...

. Additional, they

express Express or EXPRESS may refer to: Arts, entertainment, and media Films * '' Express: Aisle to Glory'', a 1998 comedy short film featuring Kal Penn * '' The Express: The Ernie Davis Story'', a 2008 film starring Dennis Quaid Music * ''Express'' ...

an ciliary

opsin Animal opsins are G-protein-coupled receptors and a group of proteins made light-sensitive via a chromophore, typically retinal. When bound to retinal, opsins become Retinylidene proteins, but are usually still called opsins regardless. Most pro ...

that is more similar to the visual ciliary opsins of vertebrate rods and cones than to the visual rhabdomeric opsins of invertebrates. Therefore, it is thought that the

urbilaterian The urbilaterian (from German ur- 'original') is the hypothetical last common ancestor of the bilaterian clade, i.e., all animals having a bilateral symmetry. Appearance Its appearance is a matter of debate, for no representative has been (or ...

, the last common ancestor of

mollusk 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 e ...

arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...

s, and

vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...

s already had ciliary photoreceptor cells. The ciliary opsin is UV-sensitive (''λ''_max = 383 nm), and the ciliary photoreceptor cells react on non-directional UV-light by making the larvae swimming down. This forms a ratio-chromatic depth-gauge with

phototaxis Phototaxis is a kind of taxis, or locomotory movement, that occurs when a whole organism moves towards or away from a stimulus of light. This is advantageous for phototrophic organisms as they can orient themselves most efficiently to receive li ...

of the rhabdomeric photoreceptor cells of the eyes. A rhabdomeric photoreceptor cell forms with a pigment cell a simple eye. A pair of these eyes mediate phototaxis in the early ''Platynereis dumerilii''

larva. In the later nectochaete larva, phototaxis is mediated by the more complex adult eyes. The adult eyes express at least three opsins: Two rhabdomeric opsins and a Go-opsin. The three opsins there mediate phototaxis all the same way via depolarization, even so a

scallop Scallop () is a common name that encompasses various species of marine bivalve mollusks in the taxonomic family Pectinidae, the scallops. However, the common name "scallop" is also sometimes applied to species in other closely related families ...

Go-opsin is known to hyperpolarize.

Chemical

''P. dumerilii'' senses chemicals with four types of organs: The antennae, the palps, the

nuchal organ The nuchal organ is a ciliated pit or groove present at the posterior end of the prostomium of annelid worms, some cephalopods, and other invertebrates. Annelids only possess one nuchal The nape is the back of the neck. In technical anato ...

s, and the tentacular

cirri Giovanni Battista Cirri (1 October 1724 – 11 June 1808) was an Italian cellist and composer in the 18th century. Biography Cirri was born in Forlì in the Emilia-Romagna Region of Italy. He had his first musical training with his brother ...

. These organs detect food and chemical cues such as alcohols, esters, amino acids, and sugars. Among the four types, the antennae are the primary chemosensory organs and sense a broad range of chemicals, while the palps are specialized on taste, which means they detect food-related chemicals. The cirri are thin thread-like head appendages and are specialized in tactile sensation, but can also give spatial information from were a chemical cue is coming, since a single stimulus can elicit in the left and right cirrus a response at a different times. The cirri also sense light: When they are shaded, the worm retreats rapidly into its tube to protect them. This behavior is called a shadow reflex. The nuchal organ is a singular ciliated pit in ''P. dumerilii''. Among annelids, nuchal organs are conserved and seem to have an important chemosensory function. However, what their exact function is, is still unclear. The signals from the four chemosensory organs are processed in a lateral region and in the

mushroom bodies The mushroom bodies or ''corpora pedunculata'' are a pair of structures in the brain of insects, other arthropods, and some annelids (notably the ragworm ''Platynereis dumerilii''). They are known to play a role in olfactory learning and memory ...

. The mushroom bodies in annelids resemble those in

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pairs ...

s by anatomy, morphology and gene expression. So probably, annelids and insects inherited mushroom bodies from their last common ancestor.

Habitat

''Platynereis dumerilii'' builds tubes on its substrate. The substrate may be algae-covered hard bottoms,

sea grass Seagrasses are the only flowering plants which grow in marine environments. There are about 60 species of fully marine seagrasses which belong to four families (Posidoniaceae, Zosteraceae, Hydrocharitaceae and Cymodoceaceae), all in the orde ...

, pelagic ''

Sargassum ''Sargassum'' is a genus of brown (class Phaeophyceae) macroalgae (seaweed) in the order Fucales. Numerous species are distributed throughout the temperate and tropical oceans of the world, where they generally inhabit shallow water and coral re ...

'' rafts in the

Sargasso Sea The Sargasso Sea () is a region of the Atlantic Ocean bounded by four currents forming an ocean gyre. Unlike all other regions called seas, it has no land boundaries. It is distinguished from other parts of the Atlantic Ocean by its charac ...

, or even rotting plant debris. ''Platynereis dumerilii'' commonly lives in depths of 0 to 5 meters, and so is typical for shallow bright infra-

littoral The littoral zone or nearshore is the part of a sea, lake, or river that is close to the shore. In coastal ecology, the littoral zone includes the intertidal zone extending from the high water mark (which is rarely inundated), to coastal areas ...

environments. However, it has been also found on a buoy at 50 meters and on rotting

seaweed Seaweed, or macroalgae, refers to thousands of species of macroscopic, multicellular, marine algae. The term includes some types of '' Rhodophyta'' (red), ''Phaeophyta'' (brown) and ''Chlorophyta'' (green) macroalgae. Seaweed species such as ...

at 100 m. It may also live in less favorable environments, like at

thermal vent A hydrothermal vent is a fissure on the seabed from which geothermally heated water discharges. They are commonly found near volcanically active places, areas where tectonic plates are moving apart at mid-ocean ridges, ocean basins, and hotspot ...

s or polluted areas near sewer outfall pipes. It dominates polluted areas and acidic areas with pH values around 6.5 fitting the preferred pH value of a subpopulation of late ''Platynereis dumerilii'' nectochaete larvae. Larvae feed on plankton, and migrate vertically in the ocean in response to changes in light, causing a daily transport of biomass.

Reproduction and Development

''Platynereis dumerilii'' is

dioecious Dioecy (; ; adj. dioecious , ) is a characteristic of a species, meaning that it has distinct individual organisms (unisexual) that produce male or female gametes, either directly (in animals) or indirectly (in seed plants). Dioecious reproductio ...

, that means it has two separate

sex Sex is the trait that determines whether a sexually reproducing animal or plant produces male or female gametes. Male plants and animals produce smaller mobile gametes (spermatozoa, sperm, pollen), while females produce larger ones (ova, oft ...

es: During

mating In biology, mating is the pairing of either opposite-sex or hermaphroditic organisms for the purposes of sexual reproduction. ''Fertilization'' is the fusion of two gametes. ''Copulation'' is the union of the sex organs of two sexually reproduc ...

, the

male Male (symbol: ♂) is the sex of an organism that produces the gamete (sex cell) known as sperm, which fuses with the larger female gamete, or ovum, in the process of fertilization. A male organism cannot reproduce sexually without access to ...

swims around the

female Female (Venus symbol, symbol: ♀) is the sex of an organism that produces the large non-motile ovum, ova (egg cells), the type of gamete (sex cell) that fuses with the Sperm, male gamete during sexual reproduction. A female has larger gamet ...

while the female is swimming in small circles. Both release eggs and sperm into the water. This is triggered by sexual

pheromone A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...

s. The eggs are then fertilized outside of the body in the water. ''Platynereis dumerilii'' has like other Nereidids no segmental gonades, the

oocyte An oocyte (, ), oöcyte, or ovocyte is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in a female fetus in the ovary during female gametogenesis. The female ...

s mature freely swimming in the body cavity (

coelom The coelom (or celom) is the main body cavity in most animals and is positioned inside the body to surround and contain the digestive tract and other organs. In some animals, it is lined with mesothelium. In other animals, such as molluscs, it r ...

), and stain the body of the mature female

epitoke Epitoky is a process that occurs in many species of polychaete marine worms wherein a sexually immature worm (the atoke) is modified or transformed into a sexually mature worm (the epitoke). Epitokes are pelagic morphs capable of sexual reproduc ...

yellow. ''Platynereis dumerilii'' develops very stereotypically between batches and therefore time can be used to stage ''Platynereis dumerilii'' larvae. However, the temperature influences the speed of development greatly. Therefore, the following developmental times are given with 18 °C as reference temperature: After 24 hours, a fertilized egg gives rise to a

larva. At 48 hours, the trochophore larva becomes a

metatrochophore A metatrochophore (;) is a type of larva developed from the trochophore larva of a polychaete annelid The annelids (Annelida , from Latin ', "little ring"), also known as the segmented worms, are a large phylum, with over 22,000 extant spe ...

larva. Both trochophore and metatrochophore swim with a ring of cilia in the water and are positively

phototactic Phototaxis is a kind of taxis, or locomotory movement, that occurs when a whole organism moves towards or away from a stimulus of light. This is advantageous for phototrophic organisms as they can orient themselves most efficiently to receive li ...

. The metatrochophore has, beside the larval eyes, already the anlagen for the more complex adult eyes of the adult worm. A day later, at 72 hours after fertilization, the metatrochophore larva becomes a nectochaete larva. The nectochaete larva already has three segments, each with a pair of

bearing

e, which serve for locomotion. The nectochaete larva can switch from positive to negative phototaxis. After five to seven days, the larvae start feeding and develop on their own speed, depending on food supply. After three to four weeks, when six segments have formed, the head is formed. Normal development is subdivided into 16 stages. ''Platynereis dumerilii'' lives for 3 up to 18 months with an average lifespan of seven months. P. dumerilii reproduces only once, and dies after delivering its gametes.

Genome

The

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 ge ...

of ''Platynereis dumerilii'' is

diploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectively ...

(2n

chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...

s) with a

haploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectively ...

set of n = 14 chromosomes. It contains approximately 1 Gbp (giga base pairs) or 10⁹ base pairs. This genome size is close to the average observed for other animals. However, compared to many classical

invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

molecular

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 ...

s, this genome size is rather large and therefore it is a challenge to identify gene regulatory elements that can be far away from the corresponding promoter. But it is

intron An intron is any nucleotide sequence within a gene that is not expressed or operative in the final RNA product. The word ''intron'' is derived from the term ''intragenic region'', i.e. a region inside a gene."The notion of the cistron .e., gene. ...

rich unlike those of ''

Drosophila melanogaster ''Drosophila melanogaster'' is a species of fly (the taxonomic order Diptera) in the family Drosophilidae. The species is often referred to as the fruit fly or lesser fruit fly, or less commonly the "vinegar fly" or "pomace fly". Starting with Ch ...

'' and ''

Caenorhabditis elegans ''Caenorhabditis elegans'' () is a free-living transparent nematode about 1 mm in length that lives in temperate soil environments. It is the type species of its genus. The name is a blend of the Greek ''caeno-'' (recent), ''rhabditis'' (ro ...

'' and thus closer to

genomes including the human genome.

References

External links

The Platynereis dumerilii Homepage
* Solène Song, Viktor Starunov, Xavier Bailly, Christine Ruta, Pierre Kerner, Annemiek J. M. Cornelissen, Guillaume Balavoine
Globins in the marine annelid Platynereis dumerilii shed new light on hemoglobin evolution in bilaterians
In: BMC Evolutionary Biology Vol. 20, Issue 165. 29 December 2020. doi:10.1186/s12862-020-01714-4. See also: :
A single gene 'invented' haemoglobin several times
On: EurekAlert! 29 December 2020. Source: CNRS {{Taxonbar, from=Q6743022 Phyllodocida Taxa named by Henri Milne-Edwards Taxa named by Jean Victoire Audouin Animals described in 1834 Model organisms