part of part of develops_from contributes to morphology of multi-tissue structure iris AAO:0010347 BTO:0000653 CALOHA:TS-0491 EFO:0004245 EMAPA:19154 EV:0100345 FMA:58235 GAID:917 MA:0000273 MESH:D007498 OpenCyc:Mx4rvVjbppwpEbGdrcN5Y29ycA TAO:0001238 The avian iris and ciliary body undergoes a transition from smooth-to-striated muscle during embryonic development [doi:dx.doi.org/10.1006/dbio.1998.9019] 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] The opaque muscular contractile diaphragm suspended in the aqueous humour in front of the lens of the eye. The organ is perforated by the pupil and continues peripherally with the ciliary body. [Dorian_AF, Elsevier's_encyclopaedic_dictionary_of_medicine, Part_B:_Anatomy_(1988)_Amsterdam_etc.:_Elsevier][VHOG] UBERON:0001769 UMLS:C0022077 VHOG:0000101 XAO:0000185 ZFA:0001238 anterior uvea irides iridial irises the adjustable membrane, composed of the stroma and pigmented epithelium, located just in front of the crystalline lens within the eye uberon ectoderm-derived structure optic vesicle anterior uvea