Pomatoceros triqueter is a species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 of tube-building annelid

Annelid

The annelids , formally called Annelida , are a large phylum of segmented worms, with over 17,000 modern species including ragworms, earthworms and leeches...

 worm in the class

Class (biology)

In biological classification, class is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order...

 Polychaeta. It is common on the north eastern coasts of the Atlantic Ocean and in the Mediterranean Sea.

Polychaetes, or marine bristle worms, have elongated bodies divided into many segments. Each segment

Segment

Segment may mean:*The divisions found in the internal section of a citrus fruit* Market segment, the smaller subgroups comprising a marketComputing*Segmentation , the division of computer memory into segments...

 may bear setae (bristles) and parapodia

Parapodium

Parapodia , singular parapodium, are paired, un-jointed lateral outgrowths from the bodies of two different invertebrate groups, which are primarily marine in habitat...

 (paddle-like appendages). Some species live freely, either swimming, crawling or burrowing, and these are known as "errant". Others live permanently in tubes, either calcareous or parchment-like, and these are known as "sedentary".

Distribution

This species is found in the Arctic

Arctic

The Arctic is a region located at the northern-most part of the Earth. The Arctic consists of the Arctic Ocean and parts of Canada, Russia, Greenland, the United States, Norway, Sweden, Finland, and Iceland. The Arctic region consists of a vast, ice-covered ocean, surrounded by treeless permafrost...

, eastern North Atlantic

Atlantic Ocean

The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

, the Mediterranean

Mediterranean Sea

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

, Adriatic

Adriatic Sea

The Adriatic Sea is a body of water separating the Italian Peninsula from the Balkan peninsula, and the system of the Apennine Mountains from that of the Dinaric Alps and adjacent ranges...

, Black

Black Sea

The Black Sea is bounded by Europe, Anatolia and the Caucasus and is ultimately connected to the Atlantic Ocean via the Mediterranean and the Aegean seas and various straits. The Bosphorus strait connects it to the Sea of Marmara, and the strait of the Dardanelles connects that sea to the Aegean...

 and Red Sea

Red Sea

The Red Sea is a seawater inlet of the Indian Ocean, lying between Africa and Asia. The connection to the ocean is in the south through the Bab el Mandeb strait and the Gulf of Aden. In the north, there is the Sinai Peninsula, the Gulf of Aqaba, and the Gulf of Suez...

, the English Channel

English Channel

The English Channel , often referred to simply as the Channel, is an arm of the Atlantic Ocean that separates southern England from northern France, and joins the North Sea to the Atlantic. It is about long and varies in width from at its widest to in the Strait of Dover...

, the North Sea

North Sea

In the southwest, beyond the Straits of Dover, the North Sea becomes the English Channel connecting to the Atlantic Ocean. In the east, it connects to the Baltic Sea via the Skagerrak and Kattegat, narrow straits that separate Denmark from Norway and Sweden respectively...

, Skagerrak

Skagerrak

The Skagerrak is a strait running between Norway and the southwest coast of Sweden and the Jutland peninsula of Denmark, connecting the North Sea and the Kattegat sea area, which leads to the Baltic Sea.-Name:...

, Kattegat

Kattegat

The Kattegat , or Kattegatt is a sea area bounded by the Jutland peninsula and the Straits islands of Denmark on the west and south, and the provinces of Västergötland, Scania, Halland and Bohuslän in Sweden on the east. The Baltic Sea drains into the Kattegat through the Øresund and the Danish...

 the Little

Little Belt

The Little Belt is a strait between the Danish island of Funen and the Jutland Peninsula.The belt is about 50 km long and 800m to 28 km wide, the maximum depth is approximately 75 m, and contains numerous small Danish islands....

 and Great Belt

Great Belt

The Great Belt is a strait between the main Danish islands of Zealand and Funen . Effectively dividing Denmark in two, the Belt was served by the Great Belt ferries from the late 19th century until the islands were connected by the Great Belt Fixed Link in 1997–98.-Geography:The Great Belt is the...

s and Øresund north east to the Bay of Kiel

Bay of Kiel

The Bay of Kiel is a bay in the southwestern Baltic Sea, off the shores of Schleswig-Holstein in Germany and the islands of Denmark. It is connected with the Bay of Mecklenburg in the east, the Little Belt in the northwest, and the Great Belt in the North....

.

Description

Pomatoceros triqueter secretes a white calcareous tube about three millimetres wide and up to twenty five millimetres long. It is smooth and usually curved with a single ridge in the middle that ends in a projection over the anterior opening. The operculum

Operculum (bryozoa)

In the bryozoan order Cheilostomata, the operculum is a calcareous or chitinous lid-like structure that protects the opening through which the polypide protrudes....

 has a shallow, dish-shaped plug. The body of the worm is brightly coloured and the crown of radiole

Radiole

A radiole is a heavily ciliated feather-like tentacle found in highly organized clusters on the crowns of Canalipalpata. Canalipalpata is an order of sessile marine polychaete worms consisting of 31 families...

s is banded with various colours. The body and crown can be withdrawn into the protective tube.

Biology

P. triqueter never leaves its tube. The action of cilia

Cilium

A cilium is an organelle found in eukaryotic cells. Cilia are slender protuberances that project from the much larger cell body....

 creates currents which circulate down the length of the tube. Respiration occurs when dissolved oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 enters through the surface of the body and through the extended branchial crown. This tube worm is a filter feeder

Filter feeder

Filter feeders are animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feeding are clams, krill, sponges, baleen whales, and many fish and some sharks. Some birds,...

 and cilia on the branchial filaments waft particles towards the central mouth. The particles are not sorted and any that are too large are removed from the mouth opening by the tip of a filament. There is a complete digestive system and like other polychaetes, P. triqueter excretes with the help of fully developed nephridia

Nephridium

A Nephridium is an invertebrate organ which occurs in pairs and function similar to kidneys. Nephridia remove metabolic wastes from an animal's body. They are present in many different invertebrate lines. There are two basic types, metanephridia and protonephridia, but there are other...

.

P. triqueter males release spermatogonia

Spermatogonium

A spermatogonium is an intermediary male gametogonium in the production of spermatozoa.There are three subtypes:...

 or primary spermatocyte

Spermatocyte

A spermatocyte is a male gametocyte, derived from a spermatogonium, which is in the developmental stage of spermatogenesis during which meiosis occurs. It is located in the seminiferous tubules of the testis.-Spermatogenesis:...

s into the sea and females release primary oocyte

Oocyte

An oocyte, ovocyte, or rarely ocyte, 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 the ovary during female gametogenesis. The female germ cells produce a primordial germ cell which undergoes a mitotic...

s. The larva

Larva

A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...

e form part of the zooplankton

Zooplankton

Zooplankton are heterotrophic plankton. Plankton are organisms drifting in oceans, seas, and bodies of fresh water. The word "zooplankton" is derived from the Greek zoon , meaning "animal", and , meaning "wanderer" or "drifter"...

 for two to three weeks in the summer when the majority of the breeding takes place, but for up to two months in the winter. The larvae then settle on the substrate and build a temporary delicate, semi-transparent tube formed of mucus and calcareous matter. This is later hardened by a secretion of calcium carbonate

Calcium carbonate

Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...

from the collar and grows at the rate of 1.5 millimetres per month. Although it may superficially give the appearance of being formed in bands, this is caused by spurts in growth interspersed with quiescent periods.