Anopla (for changes in taxonomy, see reference from 2019) has long been used as name for a

class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differentl ...

of marine worms of the

phylum In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature f ...

Nemertea 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 ...

, characterized by the absence of stylets on the

proboscis A proboscis () is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In invertebrates, the term usually refers to tubular mouthparts used for feeding and sucking. In vertebrates, a proboscis is an elong ...

, the mouth being below or behind the brain, and by having separate openings for the mouth and proboscis. The other long used class of Nemertea are the

Enopla Enopla is one of the classes of the worm phylum Nemertea, characterized by the presence of a peculiar armature of spines or plates in the proboscis. Evolution and systematics The record of nemerteans is extremely sparse, as would be expected ...

(for changes in taxonomy, see reference from 2019). Although Anopla is a

paraphyletic In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...

grouping, it is used in almost all

Scientific classification Taxonomy is the practice and science of categorization or classification. A taxonomy (or taxonomical classification) is a scheme of classification, especially a hierarchical classification, in which things are organized into groups or types. ...

s. Anopla is divided into two

orders Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...

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 ...

and

Heteronemertea Heteronemertea is a monophyletic order of about 500 species of nemertean worm. It contains genera such as ''Lineus'' and ''Cerebratulus'', and includes the largest and most muscular nemerteans. Almost all heteronemerteans have three primary bod ...

. Norenburg, J.; Gibson, R.; Herrera Bachiller, A.; Strand, M. (2019). World Nemertea Database. Anopla. Accessed through: World Register of Marine Species at: http://www.marinespecies.org/aphia.php?p=taxdetails&id=1293 on 2019-11-07 Palaeonemertea may be para- or

polyphyletic A polyphyletic group is an assemblage of organisms or other evolving elements that is of mixed evolutionary origin. The term is often applied to groups that share similar features known as homoplasies, which are explained as a result of converg ...

, consisting of 3-5 groupings and totalling about 100 species. 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 stratum overlying a longitudinal stratum. The group includes genera such as '' Cephalothrix'' in which the nerve cords are inside the body-wall longitudinal muscle, and ''

Tubulanus ''Tubulanus'' is a genus of primitive nemertean worms in the order Palaeonemertea. Species The World Register of Marine Species includes the following species in the genus: * '' Tubulanus albocinctus'' (Coe, 1904) * '' Tubulanus annulatus'' (Mo ...

'', 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 meters long, although only a few mm thick. 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 ...

grouping of about 500 species, containing genera such as ''

Lineus ''Lineus'' is a genus of nemertine worms, including the bootlace worm, arguably the longest animal alive. ''Lineus'' contains the following species: *'' Lineus acutifrons'' Southern, 1913 *'' Lineus albifrons'' Coe, 1934 *'' Lineus albocinctus ...

'' 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 including 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, middle circular, and inner longitudinal. The lateral nerve cords are outside the circular muscle, as in palaeonemerteans, but separated from the epidermis by the usually well-developed outer longitudinal muscle. A third subclass of Anopla called the Archinemertea was determined to be paraphyletic and is no longer used by most authors. A trace fossil genus called ''Archisymplectes'' from the Pennsylvanian found in central

Illinois Illinois ( ) is a U.S. state, state in the Midwestern United States, Midwestern United States. Its largest metropolitan areas include the Chicago metropolitan area, and the Metro East section, of Greater St. Louis. Other smaller metropolita ...

was formerly placed in this subclass, but is now considered a Palaeonemertea, if indeed it is an Anopla.

References

* Moore, Janet (2001) ''An introduction to the invertebrates'' (Studies in Biology) Cambridge University Press, Cambridge, UK, ; * 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 ; * 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, ; * 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; * Strand, Malin et al (2019) "Nemertean taxonomy-Implementing changes in the higher ranks, dismissing Anopla and Enopla" ''Zoologica Scripta'' Vol. 48, nr 1, s. 118-119 DOI: 10.1111/zsc.12317 {{Taxonbar, from=Q1199245