Heteronemertea is a

monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...

order of about 500

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

nemertean 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 ...

worm. It contains

genera 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 nomenclat ...

such as ''

Lineus ''Lineus'' is a genus of nemertine worms, including the bootlace worm The bootlace worm (''Lineus longissimus'') is a species of ribbon worm and one of the longest known animals, with specimens up to long being reported, although this has ...

'' and ''

Cerebratulus ''Cerebratulus'' is a genus of nemerteans belonging to the family Lineidae. The genus has cosmopolitan distribution In biogeography, cosmopolitan distribution is the term for the range of a taxon that extends across all or most of the world ...

'', and includes the largest and most

muscular Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscle ...

nemerteans. Almost all heteronemerteans have three primary body-wall muscle strata: an outer longitudinal, a middle circular, and an inner longitudinal. The lateral nerve cords are outside the circular muscle, as in

palaeonemertea Palaeonemertea is a class of primitive nemertean worm. It may be para- or polyphyletic, consisting of three to five clades and totalling about 100 species. These worms have several apparently simple features and, as their name suggests, they are ...

ns, but separated from the

epidermis The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and hypodermis. The epidermis layer provides a barrier to infection from environmental pathogens and regulates the amount of water rele ...

by the usually well-developed outer longitudinal muscle. Gorgonorhynchus repens

Taxonomy

Families within the order Heteronemertea include: * Baseodiscidae * Cerebratulidae * Gorgonorhynchidae *

Lineidae Lineidae is a family of nemertean worms. It contains the following genera: * '' Aetheolineus'' Senz, 1993 * '' Ammolineus'' Senz, 2001 * ''Antarctolineus'' Muller & Scripcariu, 1964 * ''Apatronemertes'' Wilfert & Gibson, 1974 * '' Australineus'' ...

* Mixolineidae * Panorhynchidae * Poliopsiidae * Polybrachiorhynchidae * Pussylineidae * Riseriellidae * Valenciniidae

References

Anopla {{Nemertean-stub