zonorhyncha

Zonorhyncha is an informal or historical term used to designate a proposed subdivision within the phylum Nemertea, commonly known as ribbon worms. The designation appears in some older classifications, but it is not widely used in modern nemertean systematics. In current literature, the species traditionally associated with zonorhyncha are usually placed within other nemertean groups, and zonorhyncha as a formal rank is generally considered obsolete or controversial.

The name derives from Greek zone meaning belt and rhyncha meaning snout, referencing a supposed zonation of the proboscis apparatus, the rhynchocoel. Descriptions emphasize a patterned arrangement of the rhynchus or related structures that allegedly distinguish zonorhyncha from other nemerteans. However, the exact diagnostic features are inconsistent across sources, and many authors have questioned the validity of this grouping.

Because zonorhyncha lacks stable diagnosis and consensus, it is not recognized as a formal clade in major taxonomic databases or contemporary reviews. Some historical keys treat zonorhyncha as a suborder or infraorder; others treat it as a convenience label rather than a natural grouping. Modern classifications typically treat its constituent genera within established nemertean orders or families.

See also: Nemertea, rhynchocoel, proboscis, ribbon worms.