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A funnel-shaped opening, especially the posterior nares.
(invertebrate zoology)
A protoplasmic collar surrounding the basal ends of the flagella in certain flagellates and in the choanocytes of sponges.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



an internal nasal orifice in vertebrates, including man. Choanae evolved after the development of constant or periodic breathing of air. They first arose in crossopterygian and dipnoan fish. In dipnoan embryos, grooves starting from the olfactory sacs change into canals whose internal orifices, or primary choanae, open into the oral cavity. In dipnoan fish, with aquatic respiration, air flows to the lungs through the canals. In terrestrial vertebrates, a naso-oral canal forms during embryonic development and connects with the external nasal orifices, or nostrils, to the oral cavity, where it opens into the primary choanae. In amphibians the choanae remain in this position throughout life. In mammals and in some reptiles and birds the upper part of the oral cavity into which the primary choanae open becomes separated from the lower part because of the development of the secondary hard palate; it forms the nasopharyngeal duct, which opens into the pharyngeal cavity through the secondary choanae. In crocodiles, some birds, and especially mammals the secondary choanae recede farther into the pharynx as the secondary hard palate lengthens. The formation of a nasopharyngeal duct separated from the lower part of the oral cavity and the recession of the choanae close to the larynx enable animals and humans to breathe freely when food is in the oral cavity.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
Preoperatively, there was a pinkish, vascular, and friable mass occupying the right nasal cavity, extending anteriorly up to the anterior end ofthe right middle turbinate and posteriorly occupying the choana along with extension towards the left side (Figure 3).
The telescope was navigated into the right nasal cavity, the choana reached and approx.
There was a large soft tissue mass in the right pterygoid and infratemporal fossa shown in the T2 weighted MR image (A), extending into the right posterior nasal choana (white arrow in A), with central degenerative changes.
choana: An opening (slit) in the roof of the mouth and the nasopharynx in birds.
(2,5,9,11) In birds, C gattii appears to cause localized disease, with lesions often isolated to the beak, sinus, choana, or retrobulbar space, whereas C rteoformans causes widely disseminated disease." Because multiple attempts at culture in this case proved unsuccessful, definitive species identification was not possible until PCR was performed late in the course of disease.
In both cases, nasal fibroscopy detected a polyp arising from the right inferior turbinate and extending toward the right choana. Endoscopic sinus surgery was performed in both cases to ensure a complete....
Nasal endoscopy to our surprise showed a complete atresia of right choana.
As a best practice, retailers should individually test cockatiels, love-birds, and larger psittacine birds using a PCR-based assay on a combined swab collected from the conjunctiva, choana, and cloaca (feces) during a presale quarantine period.
The mass had extended to the nasopharynx and the right posterior choana. No enlarged cervical lymph node was observed.