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.

Palaeonemertea
Cephalothrix linearis
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Nemertea
Superclass:	Pronemertea Chernyshev, 2021[1]
Class:	Palaeonemertea Hubrecht, 1879[2]
Orders and families
See text

These worms have several apparently simple features and, as their name suggests, they are often considered to be the most primitive nemerteans. The primary body-wall musculature consists of an outer circular layer overlying a longitudinal layer.

The group includes genera such as Cephalothrix in which the nerve cords are inside the body-wall longitudinal muscle, and Tubulanus, in which the nerve cords are between the outer circular muscle and the epidermis. Tubulanids are commonly encountered in rocky areas of intertidal zones in the northern hemisphere. They are often bright orange or have very distinctive banding and or stripes and can be many metres long, although only a few millimetres thick.

Taxonomy

Chernyshev (2021) placed the group in its own superclass Pronemertea, and included the following three orders and six families in the group:^[1]

• Carinomiformes
  • Carinomidae
  • Carininidae
• Tubulaniformes
  • Tubulanidae
  • Carinomellidae
• Archinemertea
  • Cephalotrichidae
  • Cephalotrichellidae

References

1. Chernyshev, A.V. (2021). "An updated classification of the phylum Nemertea". Invertebrate Zoology. 18 (3): 188–196. doi:10.15298/invertzool.18.3.01.
2. Hubrecht A. A. W. (1879). "The genera of European nemerteans critically rivised, with descriptions of several new species". Notes from the Leyden Museum. 1: 193–232.

• Thoney, Dennis A. and Schlager, Neil (eds.) (2004) "Anopla (Anoplans)" Grzimek's Animal Life Encyclopedia: Volume 1 - Lower Metazoans and Lesser Deuterostomes (2nd ed.) Thomson-Gale, Detroit, pp. 245–251 ISBN 0-7876-5777-8;
• Gibson, Ray (2002) The Invertebrate Fauna of New Zealand: Nemertea (Ribbon Worms) (NIWA Biodiversity Memoir No. 118) National Institute of Water and Atmospheric Research, Wellington, New Zealand, ISBN 0-478-23249-7 ;
• Sundberg, Per; Turbeville, J. McClintock and Lindh, Susanne (2001) "Phylogenetic Relationships among Higher Nemertean (Nemertea) Taxa Inferred from 18S rDNA Sequences" Molecular Phylogenetics and Evolution 20(3): pp. 327–334;