<Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (February 2014) (Learn how and when to remove this template message) </Td> </Tr> <P> The operculum is a series of bones found in bony fish that serves as a facial support structure and a protective covering for the gills; it is also used for respiration and feeding . </P> <P> The opercular series contains four bone segments known as the preoperculum, suboperculum, interoperculum and operculum . The preoperculum is a crescent - shaped structure that has a series of ridges directed posterodorsally to the organisms canal pores . The preoperculum can be located through an exposed condyle that is present immediately under its ventral margin; it also borders the operculum, suboperculum, and interoperculum posteriorly . The suboperculum is rectangular in shape in most bony fishy and is located ventral to the preoperculum and operculum components . It is the thinnest bone segment out of the opercular series and is located directly above the gills . The interoperculum is triangular shaped and borders the suboperculum posterodorsally and the preoperculum anterodorsally . This bone is also known to be short on the dorsal and ventral surrounding borders . </P> <P> During development the opercular series is known to be one of the first bone structures to form . In the three - spined stickleback the opercular series is seen forming at around seven days after fertilization . Within hours the formation of the shape is visible and then the individual components are developed days later . The size and shape of the operculum bone is dependent on the organism's location . For example, fresh water threespine sticklebacks form a less dense and smaller opercular series in relation to marine threespine sticklebacks . The marine threespine stickleback exhibits a larger and thicker opercular series . This provides evidence that there was an evolutionary change in the operculum bone . The thicker and more dense bone may have been favored due to selective pressures exerted from the threespine stickleback's environment . The development of the operculuar series has changed dramatically over time . The fossil record of the threespine stickleback provide the ancestral shapes of the operculum bone . Overall, the operculum bone became more triangular in shape and thicker in size over time . </P>

Where do we find an operculum in a bony fish
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