Olfactores is a clade within the

Chordata A chordate () is an animal of the phylum Chordata (). All chordates possess, at some point during their larval or adult stages, five synapomorphies, or primary physical characteristics, that distinguish them from all the other taxa. These fiv ...

that comprises the Tunicata (

Urochordata A tunicate is a marine invertebrate animal, a member of the subphylum Tunicata (). It is part of the Chordata, a phylum which includes all animals with dorsal nerve cords and notochords (including vertebrates). The subphylum was at one time ...

) and the

Vertebrata Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...

(sometimes referred to as

Craniata A craniate is a member of the Craniata (sometimes called the Craniota), a proposed clade of chordate animals with a skull of hard bone or cartilage. Living representatives are the Myxini (hagfishes), Hyperoartia (including lampreys), and the muc ...

). Olfactores represent the overwhelming majority of the phylum Chordata, as the

Cephalochordata A cephalochordate (from Greek language, Greek: κεφαλή ''kephalé'', "head" and χορδή ''khordé'', "chord") is an animal in the chordate subphylum, Cephalochordata. They are commonly called Lancelet, lancelets. Cephalochordates possess ...

are the only chordates not included in the

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

. This clade is defined by a more advanced

olfactory system The olfactory system, or sense of smell, is the sensory system used for smelling (olfaction). Olfaction is one of the special senses, that have directly associated specific organs. Most mammals and reptiles have a main olfactory system and an ac ...

which, in the immediate vertebrate generation, caused the appearance of

nostrils A nostril (or naris , plural ''nares'' ) is either of the two orifices of the nose. They enable the entry and exit of air and other gasses through the nasal cavities. In birds and mammals, they contain branched bones or cartilages called turbi ...

. A rudimentary

neural crest Neural crest cells are a temporary group of cells unique to vertebrates that arise from the embryonic ectoderm germ layer, and in turn give rise to a diverse cell lineage—including melanocytes, craniofacial cartilage and bone, smooth muscle, per ...

is present in tunicates, implying its presence in the olfactores ancestor also, as vertebrates have a true neural crest. For this reason, they are also known as

Cristozoa Cristozoa (also known as crest animals) is a grouping of animals possessing a neural crest and derivatives. It includes all the Craniata, as well as their immediate precraniate precursors. The precraniate crest animals, such ''Haikouella'' and '' ...

Olfactores hypothesis

While the hypothesis that Cephalochordata is a sister taxon to Craniata is of long standing and was once widely accepted—likely influenced by significant tunicate morphological apomorphies from other chordates, with cephalochordates even being nicknamed ‘honorary vertebrates’—studies since 2006 analyzing large

sequencing In genetics and biochemistry, sequencing means to determine the primary structure (sometimes incorrectly called the primary sequence) of an unbranched biopolymer. Sequencing results in a symbolic linear depiction known as a sequence which succ ...

datasets strongly support Olfactores as a clade. The name Olfactores comes from Latin *''olfactores'' ("smellers," from purposive supine ''olfactum'' of ''olfacio'', "to smell," with plural masculine agentive nominalizing suffix ''-tores''), due to the development of pharyngeal respiratory and sensory functions, in contrast with cephalochordates such as the

lancelet The lancelets ( or ), also known as amphioxi (singular: amphioxus ), consist of some 30 to 35 species of "fish-like" benthic filter feeding chordates in the order Amphioxiformes. They are the modern representatives of the subphylum Cephalochorda ...

which lack a respiratory system and specialized sense organs.

References

{{Taxonbar, from=Q3280581 Chordates