Anopla
Encyclopedia
Anopla are a class
of marine worms of the phylum
Nemertea
, characterized by the absence of stylet
s on the proboscis
, the mouth being below or behind the brain, and by having separate openings for the mouth and proboscis. The other class of Nemertea are the Enopla
. Although Anopla is a paraphyletic
grouping, it is used in almost all Scientific classifications. Anopla is divided into two orders
: Palaeonemertea
and Heteronemertea
.
Palaeonemertea may be para- or polyphyletic
, 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 cord
s are inside the body-wall longitudinal muscle, and Tubulanus, in which the nerve cord
s 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
grouping of about 500 species, containing genera such as Lineus
and Cerebratulus and including the largest and most muscular 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
was formerly placed in this subclass, but is now considered a Palaeonemertea, if indeed it is an Anopla.
Class (biology)
In biological classification, class is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order...
of marine worms of the phylum
Phylum
In biology, a phylum The term was coined by Georges Cuvier from Greek φῦλον phylon, "race, stock," related to φυλή phyle, "tribe, clan." is a taxonomic rank below kingdom and above class. "Phylum" is equivalent to the botanical term division....
Nemertea
Nemertea
Nemertea is a phylum of invertebrate animals also known as "ribbon worms" or "proboscis worms". Alternative names for the phylum have included Nemertini, Nemertinea and Rhynchocoela. Although most are less than long, one specimen has been estimated at , which would make it the longest animal ever...
, characterized by the absence of stylet
Stylet
A stylet is a hard, sharp, anatomical structure found in some invertebrates.For example, the word stylet or stomatostyle, is used for the primitive piercing mouthparts of some nematodes and some nemerteans...
s on the proboscis
Proboscis
A proboscis is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In simpler terms, a proboscis is the straw-like mouth found in several varieties of species.-Etymology:...
, the mouth being below or behind the brain, and by having separate openings for the mouth and proboscis. The other class of Nemertea are the Enopla
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:...
. Although Anopla is a paraphyletic
Paraphyly
A group of taxa is said to be paraphyletic if the group consists of all the descendants of a hypothetical closest common ancestor minus one or more monophyletic groups of descendants...
grouping, it is used in almost all Scientific classifications. Anopla is divided into two orders
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
: Palaeonemertea
Palaeonemertea
Palaeonemertea is an order of primitive nemertean worm. It may be para- or polyphyletic, consisting of three to five clades and totalling about 100 species....
and Heteronemertea
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....
.
Palaeonemertea may be para- or polyphyletic
Polyphyly
A polyphyletic group is one whose members' last common ancestor is not a member of the group.For example, the group consisting of warm-blooded animals is polyphyletic, because it contains both mammals and birds, but the most recent common ancestor of mammals and birds was cold-blooded...
, 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 cord
Nerve cord
Nerve cord may refer to the following structures:* in invertebrates, it refers to the ventral nerve cord, whereas* in chordates, it stands for the dorsal nerve cord....
s are inside the body-wall longitudinal muscle, and Tubulanus, in which the nerve cord
Nerve cord
Nerve cord may refer to the following structures:* in invertebrates, it refers to the ventral nerve cord, whereas* in chordates, it stands for the dorsal nerve cord....
s 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
Monophyly
In common cladistic usage, a monophyletic group is a taxon which forms a clade, meaning that it contains all the descendants of the possibly hypothetical closest common ancestor of the members of the group. The term is synonymous with the uncommon term holophyly...
grouping of about 500 species, containing genera such as Lineus
Lineus
Lineus is a genus of nemertine worms, including the bootlace worm, arguably the longest animal alive....
and Cerebratulus and including the largest and most muscular 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
Pennsylvanian
The Pennsylvanian is, in the ICS geologic timescale, the younger of two subperiods of the Carboniferous Period. It lasted from roughly . As with most other geochronologic units, the rock beds that define the Pennsylvanian are well identified, but the exact date of the start and end are uncertain...
found in central Illinois
Illinois
Illinois is the fifth-most populous state of the United States of America, and is often noted for being a microcosm of the entire country. With Chicago in the northeast, small industrial cities and great agricultural productivity in central and northern Illinois, and natural resources like coal,...
was formerly placed in this subclass, but is now considered a Palaeonemertea, if indeed it is an Anopla.