Cleithrum and scapula from a wrasse. The larger bone is the cleithrum.
The cleithrum (pl.: cleithra) is a membrane bone which first appears as part of the skeleton in primitive bony fish, where it runs vertically along the scapula.[1] Its name is derived from Greek κλειθρον = "key (lock)", by analogy with "clavicle" from Latin clavicula = "little key".
In modern fishes, the cleithrum is a large bone that extends upwards from the base of the pectoral fin and anchors to the cranium above the gills, forming the posterior edge of the gill chamber.[2] The bone has scientific use as a means to determine the age of fishes.
The lobe-finned fishes share this arrangement. In the earliest amphibians however, the cleithrum/clavicle complex came free of the skull roof, allowing for a movable neck. The cleithrum disappeared early in the evolution of reptiles, and in amniotes is very small or absent.
It has been argued based on position, muscle connectivity, and developmental origin that the nuchal element of the turtle carapace is formed from fused cleithra.[3]
Schematic illustration of turtle carapace, showing osteology on right. The nuchal bone is a proposed homolog of the cleithra.
^Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. pp. 184–186. ISBN 0-03-910284-X.
^"Fish Glossary". University of Wisconsin Sea Grant Institute. 5 February 2002. Archived from the original on 2011-03-13.
^Lyson, Tyler R.; Bhullar, Bhart-Anjan S.; Bever, Gabe S.; Joyce, Walter G.; de Queiroz, Kevin; Abzhanov, Arhat; Gauthier, Jacques A. (September 2013). "Homology of the enigmatic nuchal bone reveals novel reorganization of the shoulder girdle in the evolution of the turtle shell". Evolution & Development. 15 (5): 317–325. doi:10.1111/ede.12041. ISSN 1520-541X.
The cleithrum (pl.: cleithra) is a membrane bone which first appears as part of the skeleton in primitive bony fish, where it runs vertically along the...
is associated with the pectoral fin; they also have a bone called the cleithrum. In such fish, the paired clavicles run behind and below the gills on...
This, the type species, has a U-shaped head, with a flattened skull and cleithrum. Electrophorus voltai de Santana, Wosiacki, Crampton, Mark H. Sabaj, Dillman...
notable fossil is a large endochondral shoulder girdle consisting of the cleithrum, scapula, and coracoid (but not the interclavicle and clavicles), all...
from their ancestral external armor plates. In digitless choanates, the cleithrum, clavicle, and interclavicle are dermal and linked to the caudal part...
fusion of caudal ribs Trunk ribs mostly single headed Pectoral Region Cleithrum absent Pelvic Region Modified ilium Limb Region Tubular bone lost Entepicondylar...
third such taxa from Gondwana. Tutusius umlambo is known from a single cleithrum (a bone of the shoulder girdle) discovered at the Waterloo Farm lagerstätte...
the rays) and two movable hinge joints: a 'shoulder' joint where the cleithrum meets the radials and an 'intra-fin' joint where the radials meet the...
embryonic development is considered finished when a bone called the cleithrum becomes visible. In animals that hatch from an egg, such as birds, a young...
resulting in improved terrestrial locomotion. The early sarcopterygians' cleithrum was retained as the clavicle, and the interclavicle was well-developed...
ornamentation on the cleithrum is Parmastega, though ornamentation covers far less of the cleithrum in that taxon. The cleithrum tapers to a point anteroventrally...
skull, resulting in improved terrestrial locomotion. The crossopterygian cleithrum was retained as the clavicle, and the interclavicle was well-developed...
pachyostosis. Mesosaurus is unusual among reptiles in that it possesses a cleithrum, usually found in more primitive bony fish and tetrapods. The head of...
Global Information
