Bathylagidae (Argentiniformes)

Moritz, Timo, Buchert, Jan & Schnell, Nalani K, 2019, Unexpected diversity of median caudal cartilages in teleosts, Zoological Journal of the Linnean Society 186 (3), pp. 599-632 : 610

Bathylagidae (Argentiniformes) ( Fig. 6 )

The situation in Bathylagus euryops is like Argentina in that the lower CMC is larger than the upper one ( Fig. 6A–C ). However, the size differences between the two is much more pronounced: where the lower CMC is about three to four times the width of the hypural plates and shows a complex three-dimensional structure, the upper CMC is very small, ball-like and, in some specimens, a much reduced to a hardly visible remnant ( Fig. 6B, E ). There is one fin ray that is dorsally in contact with hypural 3 and ventrally with the lower CMC; its large base occupies the upper half of the diastemal gap ( Fig. 6C ). The upper CMC is slightly variable in its position: at about the level of the upper rim of the central fin ray, at the lower edge of hypural 3 or even dorsally to that on the distal margin of hypural 3. Due to its small size, it seems that there is no direct relation to the central ray or any other rays. The lower CMC principally resembles a bracket or a crescent moon, horizontally positioned on the upper edge of hypural 2, with its tips curved dorsally ( Fig. 6E ). The size of the cartilage, especially the extension and curvature of the tips, varies among individuals. In two specimens there are two upper CMCs at the same dorsoventral position, forming a pair left and right of the medial plain ( Fig. 6D, E ). Furthermore, in one of these, and one other specimen, there is an additional small, round cartilage in the diastema anterior to the lower CMC ( Fig. 6D ).

Figures

Figure 6. Cleared and stained caudal fins in the area of the diastema of Bathylagus euryops (Bathylagidae): A–B, DMM IE/13811, 72.4 mm SL; lateral (A) and posterior-lateral (B) views; C, DMM IE/13813, 47.5 mm SL, lateral view; D–E, DMM IE/11803, 57.7 mm SL, lateral (D) and posterior (E) views. Abbreviations: ac, accessory cartilage; hu, hypural; l-cmc, lower median caudal cartilage; lfu, lowest ray of upper caudal lobe; u-cmc, upper median caudal cartilage; ufl, upper most ray of lower caudal lobe.