Bonelliidae is a

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

of marine

worm Worms are many different distantly related bilateria, bilateral animals that typically have a long cylindrical tube-like body, no limb (anatomy), limbs, and usually no eyes. Worms vary in size from microscopic to over in length for marine ...

s (Subclass

Echiura The Echiura, or spoon worms, are a small group of ocean, marine animals. Once treated as a separate phylum, they are now considered to belong to Annelida. Annelids typically have their bodies divided into Segmentation (biology), segments, but e ...

, of the class Polychaeta, in the phylum

Annelida The annelids (), also known as the segmented worms, are animals that comprise the phylum Annelida (; ). The phylum contains over 22,000 extant species, including ragworms, earthworms, and leeches. The species exist in and have adapted to variou ...

) noted for being

sexually dimorphic Sexual dimorphism is the condition where sexes of the same species exhibit different Morphology (biology), morphological characteristics, including characteristics not directly involved in reproduction. The condition occurs in most dioecy, di ...

, 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.

Characteristics

Members of the class

are plump, unsegmented worms, commonly known as spoonworms. The mouth is at the anterior end of the trunk and a flattened

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 ...

extends forward in front of the mouth. The ventral side of the proboscis has a

ciliated 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 pr ...

channel along which food particles and

mucus Mucus (, ) is a slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands, although it may also originate from mixed glands, which contain both Serous fluid, serous and muc ...

are moved towards the mouth. Close behind the mouth are two hooked

chaeta A chaeta or cheta (; ) is a chitinous bristle or seta found on annelid worms, although the term is also frequently used to describe similar structures in other invertebrates such as arthropods. Polychaete annelids (''polychaeta'' literally me ...

e and one or two nephridial pores. The gut is much longer than the body and is folded and coiled inside 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 ...

(body cavity). The anus is at the posterior end of the body and two anal vesicles with ciliated funnels open into the

cloaca A cloaca ( ), : cloacae ( or ), or vent, is the rear orifice that serves as the only opening for the digestive (rectum), reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles, birds, cartilagin ...

. In the family Bonelliidae, the females are very much larger than the dwarf males, and in most, if not all, instances the males live on or inside the female. The anal vesicles of the females are sac-like and bear the ciliated funnels on tubules, which branch in most genera. Some

genera Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...

lack the hooked chaetae behind the mouth, and none of the genera have chaetae at the posterior end of the trunk. Most genera contain the pigment bonellin which gives them a green colour and may have antibiotic or defensive properties. Males are quite different in appearance; the minute, ciliated body consists of little except a

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 ...

, a

seminal vesicle The seminal vesicles (also called vesicular glands or seminal glands) are a pair of convoluted tubular accessory glands that lie behind the urinary bladder of male mammals. They secrete fluid that largely composes the semen. The vesicles are 5 ...

and two protonephridia. In most species, the male is found inside the genital sac of the female. The sex of a bonelliid spoonworm depends where the

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 ...

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 ...

settles. If it settles on an adult worm of its own species, it develops into a dwarf male, but if it settles anywhere else, it develops into a full-size female.

Distribution and habitat

Members of this family live in both warm and cold seas at a range of depths, with 60% of species living deeper than and some at

abyssal The abyssal zone or abyssopelagic zone is a layer of the pelagic zone of the ocean. The word ''abyss'' comes from the Greek word (), meaning "bottomless". At depths of , this zone remains in perpetual darkness. It covers 83% of the total area o ...

depths greater than . The worms inhabit burrows they dig in soft sediment, extending the flattened proboscis from the burrow along the surface of the sediment.

Genera

The

World Register of Marine Species The World Register of Marine Species (WoRMS) is a taxonomic database that aims to provide an authoritative and comprehensive catalogue and list of names of marine organisms. Content The content of the registry is edited and maintained by scien ...

includes the following genera in the family:- *'' Acanthobonellia'' Fisher, 1948 *'' Acanthohamingia'' Ikeda, 1910 *'' Achaetobonellia'' Fisher, 1953 *'' Alomasoma'' Zenkevitch, 1958 *'' Amalosoma'' Fisher, 1948 *'' Archibonellia'' Fischer, 1919 *'' Bengalus'' Biseswar, 2006 *'' Biporus'' Murina & Popkov, 2000 *'' Bonellia'' Rolando, 1822 *'' Bruunellia'' Zenkevitch, 1966 *'' Charcotus'' DattaGupta, 1981 *'' Choanostomellia'' Zenkevitch, 1964 *'' Dattaguptus'' Murina & Popkov, 2000 *'' Eubonellia'' Fisher, 1946 *'' Hamingia'' Danielssen & Koren, 1880 *'' Ikedella'' Monro, 1927 *'' Jakobia'' Zenkevitch, 1958 *'' Kurchatovus'' DattaGupta, 1977 *'' Maxmuelleria'' Bock, 1942 *'' Metabonellia'' Stephen & Edmonds, 1972 *'' Nellobia'' Fisher, 1946 *'' Prometor'' Fisher, 1948 *'' Protobonellia'' Ikeda, 1908 *'' Pseudobonellia'' Johnston & Tiegs, 1919 *'' Pseudoikedella'' Murina, 1978 *'' Sluiterina'' Monro, 1927 *'' Torbenwolffia'' Zenkevitch, 1966 *'' Vitjazema'' Zenkevitch, 1958 *'' Zenkevitchiola'' Murina, 1978

References

{{Authority control Echiurans Annelid families

Characteristics

Distribution and habitat

Genera

See also

References