Phosichthyidae

Phosichthyidae View in CoL View at ENA ( Stomiiformes ) ( Fig. 13 View Figure 13 )

In Ichthyococcus irregularis there is one single, elongated cartilage posterior to the diastemal edges of hypural 2 and hypural 3 ( Fig. 13A View Figure 13 ), occupying the space of the CMCs and therewith presumably presenting a single CMC, possibly due to an ontogenetic fusion of two CMCs. In lateral view, anterior to the bean-shaped CMC, there is an accessory small, round cartilage. The dorsal and ventral edges of the CMC articulate each with a caudal fin ray. In posterior view the CMC is dumbbell-shaped and has about the same width as the hypural plate ( Fig. 13B View Figure 13 ).

In Vinciguerria lucetia there is also one single cartilage occupying the space of the CMCs between hypural 2 and hypural 3 ( Fig. 13C View Figure 13 ). A major part of the diastema is filled by bony lamellar outgrowths of hypural 3. Only the posterior part of the diastema is spared by the outgrowth and houses the single CMC ( Fig. 13C View Figure 13 ). It is irregularly shaped in lateral view with a horizontal area where the cartilage seems less dense. One might even think there is a dorsoventral separation. However, in posterior view it becomes obvious that there is only one single, doughnut-shaped cartilage ( Fig. 13D View Figure 13 ). The outline of the hole in the cartilage shines through in lateral view and accounts for the misleading separation line and the less dense cartilage in the horizontal area. The lowermost caudal fin ray of the upper lobe articulates with the dorsal half of the cartilage, whereas the uppermost caudal fin ray of the lower lobe articulates with only the ventral margin of the cartilage.