''Metabonellia'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

of marine

spoon worms 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 ...

in the family

Bonelliidae Bonelliidae is a family of marine worms (Class Echiura, phylum Annelida) 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 gr ...

. It is a

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispec ...

genus and ''Metabonellia haswelli'' is the only species. It is commonly known as the green spoon worm and is found in shallow waters around Australia.

Description

The female worm has a sac-like trunk with a length of about and a width of . In front of the mouth is an extensible proboscis of about with a forked tip. The proboscis has a ciliated groove on the underside along which food particles are passed to the mouth. Behind the mouth, and close to the

nephridium The nephridium (plural ''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. Neph ...

, which is raised on a protuberance, are two chetae (bristles), the bases of which are buried in the muscle. The body wall has transverse rows of papillae with flattened tops. The colour of the trunk is a dark, greyish-green, the proboscis is rather paler, and the edges of the forked tip are whitish. In life, the shape and dimensions of the worm are difficult to ascertain because it is constantly wriggling about. The ovarian tissue is situated alongside the ventral blood vessel and the nephridium consists of several interconnecting sacs. The male worm is minute in comparison, being in length, and in width, with a distinct tapering tail of . It has a nephridium, a gonad and a rudimentary gut, but no chetae. The males live inside one of the sacs of the female's nephridium, where the eggs are also stored, and obtains its nutrition from the fluid in which it is immersed.

Distribution and habitat

''Metabonellia haswelli'' is found in shallow water around the coast of Australia and Tasmania. Known locations include

Port Jackson Port Jackson, consisting of the waters of Sydney Harbour, Middle Harbour, North Harbour and the Lane Cove and Parramatta Rivers, is the ria or natural harbour of Sydney, New South Wales, Australia. The harbour is an inlet of the Tasman ...

New South Wales ) , nickname = , image_map = New South Wales in Australia.svg , map_caption = Location of New South Wales in AustraliaCoordinates: , subdivision_type = Country , subdivision_name = Australia , established_title = Before federation , es ...

Boat Harbour Beach Boat Harbour Beach is a small seaside township located about from Wynyard on the north-west coast of Tasmania. " Boat Harbour" is the name of the locality which surrounds the township. In the , Boat Harbour Beach, Boat Harbour and the nearby d ...

Tasmania ) , nickname = , image_map = Tasmania in Australia.svg , map_caption = Location of Tasmania in AustraliaCoordinates: , subdivision_type = Country , subdi ...

Flinders, Victoria Flinders is a seaside town on the Mornington Peninsula in Melbourne, Victoria, Australia, south of Melbourne's Central Business District, located within the Shire of Mornington Peninsula local government area. Flinders recorded a population ...

and

Point Lonsdale Point Lonsdale is a coastal township on the Bellarine Peninsula, near Queenscliff, Victoria, Australia. The town is divided between the Borough of Queenscliffe and the City of Greater Geelong. Point Lonsdale is also one of the headlands whic ...

, Victoria. Typical habitat is on sand under rocks, in gullies, and on reefs. Its depth range is from the lower shore down to .

Ecology

This worm immerses itself in the sediment or hides its trunk under a rock, extending its proboscis with its two-pronged tip flattened over 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 (locomotion), the surface over which an organism lo ...

. It is a

deposit feeder Detritivores (also known as detrivores, detritophages, detritus feeders, or detritus eaters) are heterotrophs that obtain nutrients by consuming detritus (decomposing plant and animal parts as well as feces). There are many kinds of invertebrates, ...

, and any food particles that land on the proboscis are channelled towards the mouth.

References

{{Taxonbar, from=Q11845434 Echiurans Animals described in 1920 Monotypic animal genera