''Listriolobus pelodes'' is a species of marine

spoon worm 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 los ...

. It is found in shallow seas in the North East Pacific off the coast of California. It lives in a burrow in soft sediments.

Description

''Listriolobus pelodes'' has a plump, sausage-shaped body about long and wide. An extensible spoon-shaped

proboscis A proboscis () is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In invertebrates, the term usually refers to tubular arthropod mouthparts, mouthparts used for feeding and sucking. In vertebrates, a pr ...

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

seta In biology, setae (; seta ; ) are any of a number of different bristle- or hair-like structures on living organisms. Animal setae Protostomes Depending partly on their form and function, protostome setae may be called macrotrichia, chaetae, ...

e (bristles) projecting from the ventral surface of the body behind the mouth and a pair of

nephridiopore A nephridiopore is part of the nephridium, an excretory organ found in many organisms, such as flatworms and annelids. Polychaetes typically release their gametes into the water column using nephridiopores. Nephridia are homologous to nephrons ...

s nearby. The

anus In mammals, invertebrates and most fish, the anus (: anuses or ani; from Latin, 'ring' or 'circle') is the external body orifice at the ''exit'' end of the digestive tract (bowel), i.e. the opposite end from the mouth. Its function is to facil ...

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 Respiration may refer to: Biology * Cellular respiration, the process in which nutrients are converted into useful energy in a cell ** Anaerobic respiration, cellular respiration without oxygen ** Maintenance respiration, the amount of cellul ...

. The body is a translucent green colour and there are eight longitudinal bundles of muscle in the body wall.

Distribution

''Listriolobus pelodes'' is found along the coast of North America ranging from northern California as far south as Baja California at depths between about . It lives in a burrow in fine grained sands and mud with a high content of organic matter.

Biology

''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 Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (aquatic environment), the earthy material that exi ...

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 cilium (: cilia; ; in Medieval Latin and in anatomy, ''cilium'') is a short hair-like membrane protrusion from many types of eukaryotic cell. (Cilia are absent in bacteria and archaea.) The cilium has the shape of a slender threadlike proj ...

. 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 Peristalsis ( , ) is a type of intestinal motility, characterized by symmetry in biology#Radial symmetry, radially symmetrical contraction and relaxation of muscles that propagate in a wave down a tube, in an wikt:anterograde, anterograde dir ...

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 Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

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 and, feeding from the two burrow apertures, each worm can sweep an area of sediment of . The feeding activities of this worm, occurring as it does in large numbers, has a considerable effect on the seabed

ecosystem An ecosystem (or ecological system) is a system formed by Organism, organisms in interaction with their Biophysical environment, environment. The Biotic material, biotic and abiotic components are linked together through nutrient cycles and en ...

. The sexes are separate in ''Listriolobus pelodes''. The

gonad A gonad, sex gland, or reproductive gland is a Heterocrine gland, mixed gland and sex organ that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gon ...

s are located beside the anal vesicles and liberate

gamete A gamete ( ) is a Ploidy#Haploid and monoploid, haploid cell that fuses with another haploid cell during fertilization in organisms that Sexual reproduction, reproduce sexually. Gametes are an organism's reproductive cells, also referred to as s ...

s into the

coelom The coelom (or celom) is the main body cavity in many 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 ...

or body cavity. Here they mature and are then stored in the

nephridia The nephridium (: nephridia) is an invertebrate organ, found in pairs and performing a function similar to the vertebrate kidneys (which originated from the chordate nephridia). Nephridia remove metabolic wastes from an animal's body. Nephridia co ...

before being liberated into the sea in the late winter or spring. After fertilisation, the

eggs An egg is an organic vessel in which an embryo begins to develop. Egg, EGG or eggs may also refer to: Biology * Egg cell, the female reproductive cell (gamete) in oogamous organisms Food * Eggs as food Places * Egg, Austria * Egg, Switzerland ...

hatch into

plankton Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...

trochophore A trochophore () 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 in order to capture it more easily. ...

larva A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...

e. After several developmental stages over a period of about six months, the larvae settle on the seabed and undergo

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

into juvenile spoon worms. 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.

Ecology

A number of other invertebrates take up occupation in this spoon worm's burrow and live there as

commensal Commensalism is a long-term biological interaction (symbiosis) in which members of one species gain benefits while those of the other species neither benefit nor are harmed. This is in contrast with mutualism, in which both organisms benefit f ...

s. These include the small

crab Crabs are decapod crustaceans of the infraorder Brachyura (meaning "short tailed" in Greek language, Greek), which typically have a very short projecting tail-like abdomen#Arthropoda, abdomen, usually hidden entirely under the Thorax (arthropo ...

'' Pinnixa schmitti'', the bivalve mollusc '' Mysella tumida'' and the

polychaete worm 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 ...

'' Hesperonoe laevis''. These probably benefit from the protection from

predators Predation is a biological interaction in which 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 ...

that the burrow provides and the nutrient rich stream of water passing through the burrow. The spoon worm is preyed on by bottom feeding fish such as

flounder Flounders are a group of flatfish species. They are demersal fish, found at the bottom of oceans around the world; some species will also enter estuary, estuaries. Taxonomy The name "flounder" is used for several only distantly related speci ...

s, Dover sole (''

Microstomus pacificus The Pacific Dover sole (''Microstomus pacificus''), also called the slime sole or slippery sole, is a Pacific Ocean, Pacific flatfish of the Pleuronectidae, flounder family which ranges from Baja California to the Bering Sea. It takes its name ...

'') and bat rays ('' Myliobatis californicus''). In the 1970s, ''Listriolobus pelodes'' was found near

wastewater Wastewater (or waste water) is water generated after the use of freshwater, raw water, drinking water or saline water in a variety of deliberate applications or processes. Another definition of wastewater is "Used water from any combination of do ...

discharge outlets off

Los Angeles Los Angeles, often referred to by its initials L.A., is the List of municipalities in California, most populous city in the U.S. state of California, and the commercial, Financial District, Los Angeles, financial, and Culture of Los Angeles, ...

at densities of up to 1,500 individuals per square metre (11 square feet). The burrowing and feeding activities of these worms redistributed and aerated the sediment and promoted a more diverse community of

fauna Fauna (: faunae or faunas) is all of the animal life present in a particular region or time. The corresponding terms for plants and fungi are ''flora'' and '' funga'', respectively. Flora, fauna, funga and other forms of life are collectively ...

than would otherwise have existed in this heavily

polluted Pollution is the introduction of contaminants into the natural environment that cause harm. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). Pollutants, the component ...

area. The worms flourished for several years before disappearing from the area but their legacy of improved

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 the Ancient Greek word (), meaning "the depths". ...

diversity Diversity, diversify, or diverse may refer to: Business *Diversity (business), the inclusion of people of different identities (ethnicity, gender, age) in the workforce *Diversity marketing, marketing communication targeting diverse customers * ...

remained.

References

{{Taxonbar, from=Q2339954 Echiurans Animals described in 1946