Platytroctidae (Alepocephaliformes)

Platytroctidae (Alepocephaliformes) View in CoL View at ENA ( Fig. 3 View Figure 3 )

The situation found in Platytroctidae clearly differs from the one in Alepocephalidae . Here, two large cartilages are present and, accordingly, virtually bridge the diastema ( Fig. 3 View Figure 3 ). The upper and lower CMC almost contact each other; in this contact area they are both closely associated with the lowest fin ray of the upper caudal lobe ( Fig. 3A, E, F, G View Figure 3 ). The lower CMC further supports the upper ray of the lower lobe in almost the same way as in Alepocephalidae with the ray articulating in the area where the lower CMC meets hypural 2. The cartilages are wider in lateral dimension than the hypural plates on which they articulate with an anterior articulatory facet ( Fig. 3B–D View Figure 3 ). Seen posteriorly ( Fig. 3C, D View Figure 3 ), a complex three-dimensional structure becomes observable: the cartilages are kidney- or U-shaped, contacting each other on their ends. The articulating hemitrichs of the lowest fin ray of the upper caudal lobe are positioned with a medial peg, comparable to that in Alepocephalidae , in the area where the two cartilages approach each other. This situation is principally present in all studied specimens of Platytroctidae with only slight differences in relative size of the cartilages ( Fig. 3 View Figure 3 ).