part of part of has part has part develops_from contributes to morphology of multi-tissue structure ciliary muscle ciliary body AAO:0010341 BTO:0000260 CALOHA:TS-0694 EMAPA:19065 EV:0100346 FMA:58295 GAID:916 MA:0000264 MESH:D002924 The eye of the adult lamprey is remarkably similar to our own, and it possesses numerous features (including the expression of opsin genes) that are very similar to those of the eyes of jawed vertebrates. The lamprey's camera-like eye has a lens, an iris and extra-ocular muscles (five of them, unlike the eyes of jawed vertebrates, which have six), although it lacks intra-ocular muscles. Its retina also has a structure very similar to that of the retinas of other vertebrates, with three nuclear layers comprised of the cell bodies of photoreceptors and bipolar, horizontal, amacrine and ganglion cells. The southern hemisphere lamprey, Geotria australis, possesses five morphological classes of retinal photoreceptor and five classes of opsin, each of which is closely related to the opsins of jawed vertebrates. Given these similarities, we reach the inescapable conclusion that the last common ancestor of jawless and jawed vertebrates already possessed an eye that was comparable to that of extant lampreys and gnathostomes. Accordingly, a vertebrate camera-like eye must have been present by the time that lampreys and gnathostomes diverged, around 500 Mya.[well established][VHOG] UBERON:0001775 UMLS:C0008779 VHOG:0000102 XAO:0000186 anterior uvea ciliary bodies corpus ciliare ocular ciliary body the thickened portion of the vascular tunic, which lies between the choroid and the iris, composed of ciliary muscle and ciliary processes uberon neurectoderm ectoderm-derived structure ciliary processes anterior uvea