Sternoptychidae

Sternoptychidae View in CoL View at ENA ( Stomiiformes ) ( Fig. 11 View Figure 11 )

Polyipnus spinosus possesses two large and prominent CMCs ( Fig. 11A–C View Figure 11 ). They are somehow like an upright brick with a clear notch on the diastemal side. Thus, there are two tips facing the respective tips of the other CMC. There seems to be a strong type of connective tissue between those tips of the opposing CMCs ( Fig. 11C View Figure 11 ). In posterior view the CMCs appear massive and have about double the width of the hypural plates. The lowest ray of the upper caudal lobe articulates on the dorsal third of the upper CMC; the uppermost ray of the lower lobe in contrast articulates in the area where the lower CMC meets the fused hypural 1 and 2. There are no medially directed processes on the bases of these rays. Besides the large CMCs, there are several additional small and unpaired cartilages along the distal margin of hypural 1 + 2 and 3. They are ball-like, not as wide as the hypural plates and should probably be called post-hypural cartilages following Fujita (1989) .

The single adult specimen of Argyropelecus in this study did not stain well for cartilage ( Fig. 11D View Figure 11 ). However, we can present some data, because there are also two well-expressed CMCs. In this case, the upper one is larger than the lower one. The upper one is slightly bean-shaped in lateral view and brick-shaped when seen from the posterior side. The lower CMC is slightly bean-shaped laterally and ball-shaped in posterior view. Only the lower CMC has a slight notch on the diastemal side. The uppermost ray of the lower lobe articulates on the lower CMC. On the upper CMC there are two rays articulating: the lowest ray of the upper lobe on the ventral half of the CMC and the second lowest ray on the dorsal end of the CMC. Sternoptyx appears unique in having a large cartilage bordering the diastema posteriorly and large parts of the hypurals (see below under Development of median caudal cartilages; Fig. 25G, H View Figure 25 ).

In Maurolicus muelleri there are two rather small CMCs ( Fig. 11E View Figure 11 ) of which the upper one is missing in some specimens ( Fig. 11F View Figure 11 ). They are comma-shaped and, in contrast to most other CMCs, positioned in the rostro-caudal plane, not extending laterally. The width of the CMCs does not exceed the width of the hypural plates. The CMCs seem to be in anatomical association with the most median rays of the caudal lobes, but these rays seem not to depend on the CMCs in terms of their attachment, which equals that of the other caudal rays on the hypural plates.