''Tubulanus polymorphus'' is a species of

ribbon worm Nemertea is a phylum of animals also known as ribbon worms or proboscis worms, consisting of 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 h ...

in the phylum Nemertea. It is found in the northern Atlantic Ocean and the northern Pacific Ocean. It occurs on the lower shore down to about , on sand or gravel, under stones and among seaweed.

Description

Like other ribbon worms, ''T. polymorphus'' is not divided into segments but is soft, smooth and contractile. It is up to long but just wide, with a rounded head slightly broader than the body. There is a proboscis pore and a mouth on the underside of the head but there are no eye-spots or cephalic slits. Fresh specimens are a dark reddish-brown or orangeish-brown. Specimens preserved in alcohol lose their colour but exhibit a transverse dark band. This has a clear cut anterior margin but a posterior margin that fades gradually. A pair of sensory organs is located at the sides near the posterior margin of this band. This worm can be distinguished from other similar species by the absence of whitish bands or stripes on the body or white patches on the head, as well as by certain muscle fibres crossing over muscle layers in the dorsal part of the body wall, but not in the ventral part.

Distribution and habitat

The species occurs in water at depths down to about in both the northern Atlantic Ocean, the Mediterranean Sea and the northeastern Pacific Ocean. It is typically present on sand or gravel substrates, often under stones or among

seaweed Seaweed, or macroalgae, refers to thousands of species of macroscopic, multicellular, marine algae. The term includes some types of '' Rhodophyta'' (red), ''Phaeophyta'' (brown) and ''Chlorophyta'' (green) macroalgae. Seaweed species such as ...

s or

mussel Mussel () is the common name used for members of several families of bivalve molluscs, from saltwater and Freshwater bivalve, freshwater habitats. These groups have in common a shell whose outline is elongated and asymmetrical compared with other ...

Ecology

''Tubulanus polymorphus'' is a carnivore. On encountering a

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 wor ...

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...

or other prey item, the proboscis is everted (turned inside out) through the proboscis pore. The proboscis winds around the prey 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 and mucous cells. It is ...

and toxic secretions immobilise it. It is then passed to the mouth and swallowed whole, or if too large, digestive juices are secreted onto it and the semi-digested tissues are sucked into the mouth. The sexes are separate in this species. The females lay eggs which are fertilised externally and develop directly into juvenile worms. This ribbon worm is diurnal and makes little attempt to avoid predation. It is possible that its bright red colouration is aposemetic, giving warning that this particular ribbon worm is toxic or unpalatable. An alternative theory is that the colour may make the worm less visible to fish, which have colour vision, because the red wavelength light gets absorbed by the water and thus the worm appears dark.

References

{{Taxonbar, from=Q2610116 Palaeonemertea Animals described in 1804