Myctophidae

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 : 620-621

Myctophidae ( Myctophiformes ) ( Fig. 19 )

In the myctophids a major part of the diastema is filled by bony lamellar outgrowths of the neighbouring hypurals, mainly of hypural 3. However, the posterior part of the diastema is not closed by these outgrowths. All studied members of the family Myctophidae have two well-expressed CMCs in this posterior part of the diastema ( Fig. 19A, C, D, F ). In Benthosema glaciale the CMCs are, in posterior view, bracket- to W-shaped with their exterior tips facing towards each other ( Fig. 19B ). There is a band of strong connective tissue between these tips of the upper and lower CMC ( Fig. 19B ). The cartilages are relatively wide, more than three times the hypural width. Their middle parts articulate with the diastemal edges of hypural 2 and hypural 3, respectively. The most interior rays of the caudal lobes are placed close to the bases of the CMCs, but there seems to be no tight connection. These rays have only low medially directed bulges equalling those of the other rays. Specialized articulatory pegs are absent.

The situation is principally the same in other myctophid species ( Fig. 19C–F ). In Lampadena speculigera there are small medially directed pegs in the interior-most fin rays of the caudal lobes. In Lampanyctus crocodilus the tips of the bracketshaped CMCs are elongated bridging a major part of the diastema ( Fig. 19D, E ). In Diaphus watasei and Symbolophorus veranyi ( Fig. 19F ) the CMCs are triangular in lateral view. In some specimens (not depicted here), there are very small bean-shaped accessory cartilages directly anterior to the CMCs.

Figures

Figure 19. Cleared and stained caudal fins of Myctophidae: A–B, Benthosema glaciale, DMM IE/11136, 61.6 mm SL, overview lateral (A), median caudal cartilages in posterior view without fin rays (B); C, Lampadena speculigera, DMM IE/10198, 93.5 mm SL, lateral view; D–E, Lampanyctus crocodilus, DMM IE/11030, 94.6 mm SL, overview lateral (D), median caudal cartilages in posterior-lateral view (E); F, Symbolophorus veranyi, DMM IE/11738, 86.7 mm SL, lateral view. Abbreviations: *, ligament between CMCs; hu, hypural; l-cmc, lower median caudal cartilage; lfu, lowest ray of upper caudal lobe; phu, parhypural; u-cmc, upper median caudal cartilage; ufl, upper most ray of lower caudal lobe.