Sequential formation of epibranchial cartilages posteriorly to anteriorly. (A–I) Ventral views of dissected facial skeletal elements stained with Alcian Blue (cartilage) and Alizarin Red (bone). (A’–I’) Cropped images of one side of the corresponding A-I. The range of SL at each stage of Eb development is marked below. (A,A’) Five pairs of Cbs are seen, with the dorsal ends of five Cbs on one side marked with dots. (B,B’) A tiny piece of Eb4 at the dorsal end of the fourth Cb is indicated by black arrowheads, with the posterior dorsal tip of the fourth Cb marked with red arrowheads. (C,C’) Black arrowheads indicate growing Eb4. AECb4 is evident at the dorsal end of the fourth Cb and marked with red arrowheads. (D,D’) The emerging Eb3 at the dorsal end of the third Cb is marked with black arrowheads, with the Eb4 and AECb4 indicated by grey and red arrowheads, respectively. (E,E’) Black arrowheads mark growing Eb3, with grey and red arrowheads indicating Eb4 and AECb4, respectively. (F,F’) Eb2 appearing at the dorsal end of the second Cb is indicated by black arrowheads, along with Ebs 3 and 4 marked with grey arrowheads. Red arrowheads indicate AECb4. (G,G’) Black arrowheads indicate growing Eb2, with grey and red arrowheads indicating Ebs 3 and 4 and AECb4, respectively. (H,H’) Eb1 at the dorsal end of the first Cb is marked with black arrowheads, with Ebs 2-4 and AECb4 indicated by grey and red arrowheads, respectively. (I,I’) Black arrowheads mark growing Eb1, with growing Ebs 2-4 and AECb4 indicated by grey and red arrowheads. (J) Timeline of the development of the epibranchial cartilages. Dpf indicates the number of days post-fertilization to reach the corresponding SL, with “n” indicating the number of fish examined at each SL. The number in the colored box is the number of fish in the same SL at the corresponding developmental stages. AECb4 formation that seems to coincide with Eb4 formation is not scored. (K,K’) Ventral views of dissected facial skeletal elements stained with Alcian Blue (cartilage) and Alizarin Red (bone) at 8 mm SL. Black arrowheads indicate 4 Ebs, with red and grey arrowheads indicating AECb4 and 2 Pbs, respectively. Each facial skeletal element is labeled. (K’) Cropped image of one side of (K). Anterior is to the left. Dorsal is at the top in (A’–K’). Cb, ceratobranchial cartilage; Eb, epibranchial cartilage; AECb4, accessory element of the ceratobranchial 4; Pb, pharyngobranchial cartilage; SL, standard length; A, anterior; P, posterior; D, dorsal; V, ventral.
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