Siboglinidae is a

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. Ideal ...

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 ma ...

annelid worms whose members made up the former phyla Pogonophora and Vestimentifera (the

giant tube worm ''Riftia pachyptila'', commonly known as the giant tube worm and less commonly known as the Giant beardworm, is a marine invertebrate in the phylum Annelida (formerly grouped in phylum Pogonophora and Vestimentifera) related to tube worms ...

s). The family is composed of about 100 species of

vermiform Vermiform (ˈvərməˌfôrm) describes something shaped like a worm. The expression is often employed in biology and anatomy to describe usually soft body parts or animals that are more or less tubular or cylindrical. The word root is Latin, ''ve ...

creatures which live in thin tubes buried in sediments (Pogonophora) or in tubes attached to hard substratum (Vestimentifera) at ocean depths ranging from . They can also be found in association with

hydrothermal 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 ...

methane seep A cold seep (sometimes called a cold vent) is an area of the ocean floor where hydrogen sulfide, methane and other hydrocarbon-rich fluid seepage occurs, often in the form of a brine pool. ''Cold'' does not mean that the temperature of the seep ...

s, sunken plant material, and whale carcasses. The first specimen was dredged from the waters of what is now

Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Guine ...

in 1900. These specimens were given to French zoologist

Maurice Caullery Maurice Jules Gaston Corneille Caullery (5 September 1868, Bergues – 13 July 1958, Paris) was a French biologist. Biography He was born in Bergues in north France on 5 September 1868. His early education was in Douai. He began as a lectu ...

, who studied them for nearly 50 years.

Anatomy

Most siboglinids are less than in diameter, but in length. They inhabit tubular structures composed of

chitin Chitin ( C8 H13 O5 N)n ( ) is a long-chain polymer of ''N''-acetylglucosamine, an amide derivative of glucose. Chitin is probably the second most abundant polysaccharide in nature (behind only cellulose); an estimated 1 billion tons of chit ...

and fixed to rocks or substrate. The tubes are often clustered together in large colonies. Their bodies are divided into four regions. The anterior end is called the cephalic lobe, which bears from one to over 200 thin branchial

cilia 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 pro ...

ted

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, each with tiny side branches known as pinnules. Behind this is a glandular forepart, which helps to secrete the tube. The main part of the body is the trunk, which is greatly elongated and bears various annuli, papillae, and ciliary tracts. Posterior to the trunk is the short metamerically segmented

opisthosoma The opisthosoma is the posterior part of the body in some arthropods, behind the prosoma (cephalothorax). It is a distinctive feature of the subphylum Chelicerata (arachnids, horseshoe crabs and others). Although it is similar in most respects to ...

, bearing external paired

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 such ...

e, which apparently help to anchor the animal to the base of its tube. The body cavity has a separate compartment in each of the first three regions of the body, and extends into the tentacles. The opisthoma has a

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, i ...

ic chamber in each of its five to 23 segments, separated by

septa The Southeastern Pennsylvania Transportation Authority (SEPTA) is a regional public transportation authority that operates bus, rapid transit, commuter rail, light rail, and electric trolleybus services for nearly 4 million people in five cou ...

. The worms have a complex

closed circulatory system The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...

and a well-developed

nervous system In biology, the nervous system is the highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from different parts of its body. The nervous system detects environmental changes ...

, but as adults, siboglinids completely lack a mouth, gut, and anus.

Evolution

The family Siboglinidae has been difficult to place in an evolutionary context. After examination of genetic differences between annelids, Siboglinidae were placed within the order

Polychaeta 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 m ...

by scientific consensus. The fossil record along with

molecular clock The molecular clock is a figurative term for a technique that uses the mutation rate of biomolecules to deduce the time in prehistory when two or more life forms diverged. The biomolecular data used for such calculations are usually nucleotid ...

s suggest the family has

Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceo ...

(250 – 66 Mya) or

Cenozoic The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configurat ...

(66 Mya – recent) origins. However, some fossils of crystallized tubes are attributed to early Siboglinidae dating back to 500 Mya. Molecular work aligning five genes has identified four distinct

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

s within Siboglinidae. The clades are ''Vestimentifera'', ''Sclerolinum'', ''Frenulata'', and ''

Osedax ''Osedax'' is a genus of deep-sea siboglinid polychaetes, commonly called boneworms, zombie worms, or bone-eating worms. ''Osedax'' is Latin for "bone-eater". The name alludes to how the worms bore into the bones of whale carcasses to reach e ...

''. These clades represent the four tracks evolution has followed within the Siboglinidae. Vestimentiferans live in vent and seep habitats. Separation of vestimentiferans into seep- and deep-sea-dwelling clades is still debated due to some phylogenies based on sequencing data placing the genera along a continuum. ''Sclerolinum'' is a monogeneric clade living on organic-rich remains. Frenulates live in organic-rich sediment habitats. ''Osedax'' is a monogeneric clade specialized in living on whale bones, although recent evidence shows them living on fish bones as well.

Vestimentiferans

Like other tube worms, vestimentiferans are

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning ...

marine creatures. ''

Riftia pachyptila ''Riftia pachyptila'', commonly known as the giant tube worm and less commonly known as the Giant beardworm, is a marine invertebrate in the phylum Annelida (formerly grouped in phylum Pogonophora and Vestimentifera) related to tube worms ...

'', a vestimentiferan, is known only from the

systems.

Anatomy of vestimentiferans

Vestimentiferan bodies are divided into four regions: the obturaculum, vestimentum, trunk, and opisthosome. The main trunk of the body bears wing-like extensions. Unlike other siboglinids that never have a

digestive tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans and ...

, they have one that they completely lose during

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

. The obturaculum is the first anterior body part. It is possible that developmentally the obturaculum structures which in many tube worms include an organ to block the entrance to the tube is an outgrowth of the vestimentum rather than the first body segment. The vestimentum, from which the group's name is derived, is a wing-like body part with glands that secrete the tube. In a ventroanterior position in the vestimentum is the brain which is postulated to be simpler than relatives that maintain a gut in the adult form. The opisthosome is the anchoring rear body part.

Vestimentiferan ecology

Their primary nutrition is derived from the sulfide-rich fluids emanating from the hydrothermal vents where they live. The sulfides are metabolized by

symbiotic Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasi ...

hydrogen sulfide- or methane-oxidizing bacteria living in an internal organ, the

trophosome A trophosome is a highly vascularised organ found in some animals that houses symbiotic bacteria that provide food for their host. Trophosomes are located in the coelomic cavity in the vestimentiferan tube worms ( Siboglinidae, e.g. the giant tube ...

. One gram of trophosome tissue can contain one billion bacteria. How the worms instigate their relationship with the bacteria is not completely understood. The bacteria appear to colonize the host animal larvae after they have settled on a surface, entering them through their skin. This method of entry, known as horizontal transmission, means that each organism may have different species of bacteria assisting in this symbiosis. However, these bacteria all play similar roles in sustaining the vestimentiferans. Endosymbionts have a wide variety of metabolic genes, which may allow them to switch between autotrophic and heterotrophic methods of nutrient acquisition. When the host dies, the bacteria are released and return to the free-living population in the seawater. Discovery of the hydrothermal vents in the eastern Pacific Ocean was quickly followed by the discovery and description of new vestimentiferan tubeworm species. These tubeworms are one of the most dominant organisms associated with the hydrothermal vents in the Pacific Ocean. Tubeworms anchor themselves to the substratum of the hydrocarbon seep by roots located at the basal portion of their bodies. Intact tubeworm roots have proven very difficult to obtain for study because they are extremely delicate, and often break off when a tubeworm is removed from hypothermal vent regions. How long the roots of the tube worms can grow is unknown, but roots have been recovered longer than 30 m. A single aggregation of tubeworms can contain thousands of individuals, and the roots produced by each tubeworm can become tangled with the roots of neighbouring tubeworms. These mats of roots are known as "ropes", and travel down the tubes of dead tubeworms, and run through holes in rocks. The diameter and wall thickness of the tubeworm roots do not appear to change with distance from the trunk portion of the tubeworm's body. Like the trunk portion of the body, the roots of the vestimentiferan tubeworms are composed of

crystallites, which support and protect the tubeworm from predation and environmental stresses. Tubeworms build the external chitin structure themselves by secreting chitin from specialized glands located in their body walls.

Genera

* ''

'' * '' Frenulata'' ** '' Birsteinia'' ** '' Bobmarleya'' ** '' Choanophorus'' ** '' Crassibrachia'' ** '' Cyclobrachia'' ** '' Diplobrachia'' ** '' Galathealinum'' ** '' Heptobrachia'' ** '' Lamellisabella'' ** '' Nereilinum'' ** '' Oligobrachia'' ** '' Paraescarpia'' ** '' Polybrachia'' ** '' Siboglinoides'' ** '' Siboglinum'' ** '' Siphonobrachia'' ** '' Spirobrachia'' ** '' Unibrachium'' ** '' Volvobrachia'' ** '' Zenkevitchiana'' * '' Sclerolinum'' * '' Vestimentifera'' ** '' Alaysia'' ** '' Arcovesia'' ** '' Escarpia'' ** ''

Lamellibrachia ''Lamellibrachia'' is a genus of tube worms related to the giant tube worm, ''Riftia pachyptila''. They live at deep-sea cold seeps where hydrocarbons (oil and methane) leak out of the seafloor, and are entirely reliant on internal, sulfide-oxi ...

'' ** '' Oasisia'' ** '' Ridgeia'' ** ''

Riftia ''Riftia pachyptila'', commonly known as the giant tube worm and less commonly known as the Giant beardworm, is a marine invertebrate in the phylum Annelida (formerly grouped in phylum Pogonophora and Vestimentifera) related to tube worms ...

'' ** '' Tevnia''

References

External links

* * {{Authority control Polychaetes Chemosynthetic symbiosis Annelid families