| Listriolobus pelodes | |
|---|---|
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Annelida |
| Clade: | Pleistoannelida |
| Clade: | Sedentaria |
| Subclass: | Echiura |
| Order: | Echiuroidea |
| Family: | Echiuridae |
| Genus: | Listriolobus |
| Species: | L. pelodes |
| Binomial name | |
| Listriolobus pelodes Fisher, 1946 [1] | |
Listriolobus pelodes is a species of marine spoon worm. It is found in shallow seas in the North East Pacific off the coast of California. It lives in a burrow in soft sediments.
Listriolobus pelodes has a plump, sausage-shaped body about 4 centimetres (1.6 in) long and 2 to 3 centimetres (0.79 to 1.18 in) wide. An extensible spoon-shaped proboscis projects from the anterior (front) end of the body and the mouth is at its base on the ventral side. There is a pair of hooked setae (bristles) projecting from the ventral surface of the body behind the mouth and a pair of nephridiopores nearby. The anus is at the posterior end of the body. There are two anal vesicles on either side of the rear end of the gut which are used for respiration. The body is a translucent green colour [2] and there are eight longitudinal bundles of muscle in the body wall. [3]
Listriolobus pelodes is found along the coast of North America ranging from northern California as far south as Baja California at depths between about 18 to 155 metres (59 to 509 ft). It lives in a burrow in fine grained sands and mud with a high content of organic matter. [3]
Listriolobus pelodes lives in a U-shaped burrow in the sediment. Its body remains below the surface while it extends its flexible proboscis across the substrate with the ventral side upwards. Sediment is scooped up by the proboscis and is wafted along a central groove to the mouth by the action of cilia. The sediment passes through the gut where the nutritive parts are digested and absorbed, and the residue is ejected through the anus as faecal pellets. The worm creates a current of water through the tube by peristaltic movements and this washes the pellets out of the second aperture of the tube. They accumulate nearby in little piles, the presence of which may show where these spoon worms are buried. The faecal pellets get ingested during further feeding activities and it is probable that rapidly growing bacteria and other micro-organisms form part of the diet. Other movements of the body wall draw water into and out of the anal vesicles and respiratory gases are exchanged. The worm periodically reverses its position in its burrow. The proboscis can extend to a length of 20 centimetres (7.9 in) and, feeding from the two burrow apertures, each worm can sweep an area of sediment of 0.25 square metres (2.7 sq ft). The feeding activities of this worm, occurring as it does in large numbers, has a considerable effect on the seabed ecosystem. [3]
The sexes are separate in Listriolobus pelodes. The gonads are located beside the anal vesicles and liberate gametes into the coelom or body cavity. Here they mature and are then stored in the nephridia before being liberated into the sea in the late winter or spring. [3] After fertilisation, the eggs hatch into planktonic trochophore larvae. After several developmental stages over a period of about six months, the larvae settle on the seabed and undergo metamorphosis into juvenile spoon worms. [4] They seem to be attracted to settle in areas of fine, nutrient-rich sediment but the mechanism for this discrimination is unclear. The juveniles become sexually mature in another six to twelve months. [3]
A number of other invertebrates take up occupation in this spoon worm's burrow and live there as commensals. These include the small crab Pinnixa schmitti , the bivalve mollusc Mysella tumida and the polychaete worm Hesperonoe laevis . These probably benefit from the protection from predators that the burrow provides and the nutrient rich stream of water passing through the burrow. [3]
The spoon worm is preyed on by bottom feeding fish such as flounders, Dover sole ( Microstomus pacificus ) and bat rays ( Myliobatis californicus ). [3]
In the 1970s, Listriolobus pelodes was found near wastewater discharge outlets off Los Angeles at densities of up to 1,500 individuals per square metre (11 square feet). [5] The burrowing and feeding activities of these worms redistributed and aerated the sediment and promoted a more diverse community of fauna than would otherwise have existed in this heavily polluted area. The worms flourished for several years before disappearing from the area but their legacy of improved benthic diversity remained. [5]
The Sipuncula or Sipunculida is a class containing about 162 species of unsegmented marine annelid worms. Sipuncula was once considered a phylum, but was demoted to a class of Annelida, based on recent molecular work.
The Echiura, or spoon worms, are a small group of marine animals. Once treated as a separate phylum, they are now considered to belong to Annelida. Annelids typically have their bodies divided into segments, but echiurans have secondarily lost their segmentation. The majority of echiurans live in burrows in soft sediment in shallow water, but some live in rock crevices or under boulders, and there are also deep sea forms. More than 230 species have been described. Spoon worms are cylindrical, soft-bodied animals usually possessing a non-retractable proboscis which can be rolled into a scoop-shape to feed. In some species the proboscis is ribbon-like, longer than the trunk and may have a forked tip. Spoon worms vary in size from less than a centimetre in length to more than a metre.
The gastrotrichs, commonly referred to as hairybellies or hairybacks, are a group of microscopic (0.06–3.0 mm), cylindrical, acoelomate animals, and are widely distributed and abundant in freshwater and marine environments. They are mostly benthic and live within the periphyton, the layer of tiny organisms and detritus that is found on the seabed and the beds of other water bodies. The majority live on and between particles of sediment or on other submerged surfaces, but a few species are terrestrial and live on land in the film of water surrounding grains of soil. Gastrotrichs are divided into two orders, the Macrodasyida which are marine, and the Chaetonotida, some of which are marine and some freshwater. Nearly 800 species of gastrotrich have been described.
Nemertea is a phylum of animals also known as ribbon worms or proboscis worms, consisting of about 1300 known species. Most ribbon worms are very slim, usually only a few millimeters wide, although a few have relatively short but wide bodies. Many have patterns of yellow, orange, red and green coloration. The foregut, stomach and intestine run a little below the midline of the body, the anus is at the tip of the tail, and the mouth is under the front. A little above the gut is the rhynchocoel, a cavity which mostly runs above the midline and ends a little short of the rear of the body. All species have a proboscis which lies in the rhynchocoel when inactive but everts to emerge just above the mouth to capture the animal's prey with venom. A highly extensible muscle in the back of the rhynchocoel pulls the proboscis in when an attack ends. A few species with stubby bodies filter feed and have suckers at the front and back ends, with which they attach to a host.
The acorn worms or Enteropneusta are a hemichordate class of invertebrates consisting of one order of the same name. The closest non-hemichordate relatives of the Enteropneusta are the echinoderms. There are 111 known species of acorn worm in the world, the main species for research being Saccoglossus kowalevskii. Two families—Harrimaniidae and Ptychoderidae—separated at least 370 million years ago.
Enopla is one of the classes of the worm phylum Nemertea, characterized by the presence of a peculiar armature of spines or plates in the proboscis.
Urechis unicinctus, known as the fat innkeeper worm or penis fish, is a species of marine spoon worm in East Asia. It is also known as garloid colloquially. It is found in Bohai Gulf of China and off the Korean and Hokkaido coasts. It is not to be confused with a closely related species, Urechis caupo, which occurs on the western coast of North America and shares common names. The body is about 10–30 centimetres (3.9–11.8 in) long, cylindrical in shape and yellowish-brown in color. On the surface of the body there are many small papillae.
Phascolopsis gouldii is a species of unsegmented benthic marine worm, also known as a peanut worm or star worm. It lives in burrows in muddy sand in shallow waters off North America.
Lanice conchilega, commonly known as the sand mason worm, is a species of burrowing marine polychaete worm. It builds a characteristic tube which projects from the seabed, consisting of cemented sand grains and shell fragments with a fringe at the top.
Eudistylia is a genus of marine polychaete worms. The type species is Eudistylia gigantea, now accepted as Eudistylia vancouveri. This worm lives in a parchment-like tube with a single opening from which a crown of tentacles projects when the worm is submerged. It is a sessile filter feeder. the Eudistylia Vancouveri is unique because it has an opiculum which makes it possible to fully retract into the tube when predators are sensed.
Phoronis psammophila is a species of marine horseshoe worm in the phylum Phoronida. It lives in a tube projecting from the sea floor in shallow seas around the world.
Harrimania planktophilus is a marine acorn worm in the family Harrimaniidae. It lives in a burrow in sediment on the sea floor. It is only known from western Canada and was first described by Cameron in 2002. The species name is from the Greek and translates as "lover of plankton".
Scolelepis squamata is a species of polychaete worm in the family Spionidae. It occurs on the lower shore of coasts on either side of the Atlantic Ocean.
Cerebratulus marginatus is a proboscis worm in the family Lineidae. This ribbon worm has an Arctic distribution, and in the North Atlantic Ocean ranges as far south as Cape Cod and the Mediterranean Sea while in the Pacific Ocean it extends southwards to California.
Bonelliidae is a family of marine worms noted for being sexually dimorphic, with males being tiny in comparison with the females. They occupy burrows in the seabed in many parts of the world's oceans, often at great depths.
Urechis caupo is a species of spoon worm in the family Urechidae, commonly known as the innkeeper echiuran, the fat innkeeper worm, the innkeeper worm, or the penis fish. It is found in shallow water on the west coast of North America, between southern Oregon and Baja California, where it forms a U-shaped burrow in the sediment and feeds on plankton using a mucus net.
Ochetostoma erythrogrammon is a species of spoon worm in the family Thalassematidae. It is found in shallow water in the Atlantic Ocean, the Mediterranean Sea, and the Indian and Pacific Oceans, burrowing in soft sediment.
Echiurus echiurus is a species of spoon worm in the family Echiuridae. It is found in the North Atlantic Ocean and a subspecies is found in Alaska. It burrows into soft sediment and under boulders and stones in muddy places.
Poecilochaetus serpens is a species of marine polychaete worm in the family Poecilochaetidae. It is a benthic worm that burrows into soft sediment.
Paraleptopentacta elongata is a species of sea cucumber in the family Cucumariidae. It is found in the northeastern Atlantic Ocean and parts of the Mediterranean Sea. It is an infaunal species, occupying a burrow in the seabed, from which its anterior and posterior ends project.