The
Lophotrochozoa are a major grouping of
protostomeProtostomia are a clade of animals. Together with the deuterostomes and a few smaller phyla, they make up the Bilateria, mostly comprising animals with bilateral symmetry and three germ layers...
animals. The taxon was introduced in 1995 in a paper by Kenneth M Halanych
et al. based on molecular data. Molecular evidence such as a result of studies of the evolution of small-subunit
ribosomal RNARibosomal RNA is the central component of the ribosome, the protein manufacturing machinery of all living cells. The function of the rRNA is to provide a mechanism for decoding mRNA into amino acids and to interact with the tRNAs during translation by providing peptidyl transferase activity.The...
(rRNA) supports the
monophylyA clade is a term used in modern alpha taxonomy, the scientific classification of living and fossil organisms, to describe a monophyletic group, defined as a group consisting of a single common ancestor and all its descendants.[The term "monophyletic group" is used in this article...]
of the
phylaIn biology, a phylum ["Phylum" is adopted from the Greek phylai, the clan-based voting groups in Greek city-states.] is a taxonomic rank below Kingdom and above Class...
listed in the infobox shown at right.
The word "lophotrochozoan" is sometimes equated with spiralian.
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The
Lophotrochozoa are a major grouping of
protostomeProtostomia are a clade of animals. Together with the deuterostomes and a few smaller phyla, they make up the Bilateria, mostly comprising animals with bilateral symmetry and three germ layers...
animals. The taxon was introduced in 1995 in a paper by Kenneth M Halanych
et al. based on molecular data. Molecular evidence such as a result of studies of the evolution of small-subunit
ribosomal RNARibosomal RNA is the central component of the ribosome, the protein manufacturing machinery of all living cells. The function of the rRNA is to provide a mechanism for decoding mRNA into amino acids and to interact with the tRNAs during translation by providing peptidyl transferase activity.The...
(rRNA) supports the
monophylyA clade is a term used in modern alpha taxonomy, the scientific classification of living and fossil organisms, to describe a monophyletic group, defined as a group consisting of a single common ancestor and all its descendants.[The term "monophyletic group" is used in this article...]
of the
phylaIn biology, a phylum ["Phylum" is adopted from the Greek phylai, the clan-based voting groups in Greek city-states.] is a taxonomic rank below Kingdom and above Class...
listed in the infobox shown at right.
Terminology
The word "lophotrochozoan" is sometimes equated with spiralian. When used in a broader sense (
sensuSensu is a Latin term meaning "in the sense of".It is used in fields including biology, geology and law in the phrases sensu stricto or stricto sensu , and sensu lato or lato sensu ....
lato), it can include rotifers and platyhelminthes. When used
sensu stricto, it refers to a subgroup of Spirilia.
Groups
The Lophotrochozoa comprise two groups, the trochozoans and the lophophorata. The exact relationships between the different phyla are not entirely certain. However, it appears that neither the lophophorates nor the trochozoa are monophyletic groups by themselves, but are mixed together.
- Trochozoans produce trochophore
A trochophore is a type of free-swimming planktonic marine larva with several bands of cilia.By moving their cilia rapidly, a water eddy is created. In this way they control the direction of their movement...
larvaA larva is a young form of animal with indirect development, going through or undergoing metamorphosis ....
e, which have two bands of ciliaA cilium is an organelle found in eukaryotic cells. Cilia are tail-like projections.There are two types of cilia: motile cilia and non-motile, or primary, cilia, which typically serve as sensory organelles...
around their middle. Previously these were treated together as the Trochozoa, together with the arthropodAn arthropod is an invertebrate that has an exoskeleton , a segmented body, and jointed attachments called appendages. Arthropods are animals belonging to the Phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
s, which do not produce trochophore larvae but were considered close relatives of the annelidThe annelids, collectively called Annelida , are a large phylum of segmented worms, with over 17,000 modern species including ragworms, earthworms and leeches. They are found in marine environments from tidal zones to hydrothermal vents, in freshwater, and in moist terrestrial environments...
s because they are both segmented. However, they show a number of important differences, and the arthropods are now placed separately among the EcdysozoaThe Ecdysozoa are a grouping of protostome animals, including the Arthropoda , Nematoda, and several smaller phyla. They were first defined by Aguinaldo et al. in 1997, based mainly on trees constructed using 18S ribosomal RNA genes...
. The Trochozoa include the NemerteaNemertea is a phylum of invertebrate animals also known as ribbon worms or proboscis worms.
Most of the 1,400 or so species are marine, with a few living in fresh water and a small number of terrestrial forms; they are found in all marine habits, and throughout the world's oceans...
, MolluscaMolluscs
[Spelled mollusk in the USA, see reasons given in Rosenberg's ; for the spelling "mollusc" see the reasons given by .] are animals belonging to the phylum Mollusca. There are around 93,000 recognized extant species, making it the largest marine phylum with about 23% of...
, SipunculaThe Sipuncula or Sipunculida, sipunculid worms or peanut worms, are a phylum containing 144-320 species of bilaterally symmetrical, unsegmented marine worms...
, EchiuraThe Echiura, or spoon worms, are a small group of marine animals. They are often considered to be a group of annelids, although they lack the segmented structure found in other members of that group, and so may also be treated as a separate phylum...
, PogonophoraSiboglinidae, also known as the beard worms, is a family of polychaete annelid worms whose members made up the former phyla Pogonophora and Vestimentifera. They are composed of about 100 species of vermiform creatures and live in thin tubes buried in sediments at ocean depths from 100 to 10,000 m...
and Annelida.
- The Lophophorata are united by the presence of a lophophore
The lophophore is a characteristic feeding organ possessed by three major groups of animals: the Brachiopoda, Bryozoa, and Phoronida . All lophophores are found in aquatic organisms.-Characteristics:...
, a fan of ciliated tentacles surrounding the mouth, and so were treated together as the lophophorates. They are unusual in showing radial cleavage, and some authors considered them deuterostomeDeuterostomes are a superphylum of animals. They are a subtaxon of the Bilateria branch of the subregnum Eumetazoa, and are opposed to the protostomes...
s, before RNARibonucleic acid is a biologically important type of molecule that consists of a long chain of nucleotide units. Each nucleotide consists of a nitrogenous base, a ribose sugar, and a phosphate...
trees placed them together with the trochozoans. The Lophophorata include the BryozoaThe Bryozoa, also known as Ectoprocta, are a phylum of aquatic animals, typically about long, that sieve food particles out of the water using a retractable lophophore, a "crown" of tentacles lined with cilia. Most marine species live in tropical waters, but a few occur in oceanic trenches and...
, EntoproctaEntoprocta, whose name means "anus inside", is a phylum of mostly sessile aquatic animals, ranging from long. Mature individuals are goblet-shaped, on relatively long stalks. They have a "crown" of solid tentacles whose cilia generate water currents that draw food particles towards the mouth,...
, Phoronida, and Brachiopoda.
Other phyla are included on the basis of molecular data.
A phylogenetic tree of the Lophotrochozoa as suggested by Dunn et al. (2008)
Further reading
- Podsiadlowski R. 2009. Phylogeny and mitochondrial gene order variation in Lophotrochozoa in the light of new mitogenomic data from Nemertea
Nemertea is a phylum of invertebrate animals also known as ribbon worms or proboscis worms.
Most of the 1,400 or so species are marine, with a few living in fresh water and a small number of terrestrial forms; they are found in all marine habits, and throughout the world's oceans...
. BMC Genomics 2009, 10:364.