''Bonellia viridis'', the green spoonworm, is a marine

worm Worms are many different distantly related bilateral animals that typically have a long cylindrical tube-like body, no limbs, and no eyes (though not always). Worms vary in size from microscopic to over in length for marine polychaete wo ...

(class

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 ar ...

, phylum Annelida) noted for displaying exceptional

sexual dimorphism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most an ...

and for the biocidal properties of a pigment in its skin.Murina, G. (2008). Bonellia viridis Rolando, 1821. In: Read, G.; Fauchald, K. (Ed.) (2016). World Polychaeta database. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=110363 on 2016-05-28

Distribution

The species is wide-ranging, found in the north-eastern

Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...

and the

Mediterranean Sea The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the ...

Description

The pale- to dark-green female, with a 15 cm-long, round or sausage-shaped body, lives on the sea-floor at a depth of 10 to 100 metres, concealed by burrowing in gravel or hiding in rock crevasses or burrows abandoned by other animals. It has two anchoring hooks underneath its body and an extensible feeding proboscis up to 10 times its body-length. It is mainly a detritivore, feeding also on small animals. The male is rarely observed: it has a flat, unpigmented body which grows to only 1–3 mm, taken up mostly by reproductive organs and devoid of other structures; it lives on or inside the body of a female.

Bonellin as a biocide

The adult ''Bonellia'' female produces a vivid green pigment in its skin, known as bonellin. This chemical, concentrated mostly in the proboscis, is highly toxic to other organisms, capable of paralyzing small animals. In the presence of light, bonellin is a very effective biocide, killing bacteria, larva of other organisms, and red blood cells in laboratory tests. It is currently being investigated as a possible model for novel antibiotics. Most larvae, however, come in contact with the bonellin in the skin of an adult female—its body or its roving, bonellin-rich proboscis—and are masculinised by this exposure. The chemical causes these larvae to develop into the tiny males, which cling to the female's body or are sucked inside it by the feeding tube, to spend the remainder of their lives inside her genital sac, producing sperm to fertilize her eggs, reliant on her for all other needs.Ludek Berec, Patrick J. Schembri, David S. Boukal (2005)
Sex determination in ''Bonellia viridis'' (Echiura: Bonelliidae): population dynamics and evolution
. Oikos 108 (3), 473–484 The sex of a green spoonworm is thus determined by external, environmental factors (the presence or absence of bonellin), not by internal, genetic factors (

chromosomes A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...

), as is the case with most other sexually-differentiated organisms. This environmental sex determination helps green spoonworm populations respond to the availability of burrows.

References

* van der Land, J. (2001). Echiura, in: Costello, M.J. et al. (Ed.) (2001). European register of marine species: a check-list of the marine species in Europe and a bibliography of guides to their identification. Collection Patrimoines Naturels, 50: pp. 178

External links

* {{Taxonbar, from=Q2341608 Echiurans Animals described in 1821