Figure 1. Cheirolepis, a Middle Devonian ancestor to the viperfish.

Yes, it’s another great grandson
of Cheirolepis (Fig. 1), one of the earliest known bony fish. Earlier we looked at another great, grandson deep sea fish, Malacosteus.

Figure 2. Chauliodus diagram from Gregory 1938. Note the convergent loss of cheek bones in this Cheirolepis clade member.

Chauliodus sloani (Forster in Bloch and Schneider 1801, up to 60cm in length, subset Fig. 2-4) is the extant viperfish. A tiny glowing lure from the anterior dorsal fin lure deep sea fish to the oversized teeth. Scales and maxillary teeth are retained. Apparently the temporal series (intertemporal, supratemporal and tabular) were not retained, which is almost unique among fish. The anterior dorsal fin is new based on comparisons to Cheirolepis (Fig. 1). Note the evolution of the heterocercal tail to a diphycercal tail, only one of many such convergent instances.

Figure 3. Chauliodus, the viperfish, in vivo.

Biting is a big deal with Chauliodus
as those jaws go through some gymnastics at maximum aperture (Fig. 4).

Figure 4. Viperfish posed as if biting its prey attracted to its first dorsal fin lure.

This nesting
and several others to come are greatly simplifying the fish family tree. I will list the many exciting changes shortly.

References
Forster JR 1801. in Bloch, ME and Schneider JG editors, Systema Ichthyologiae Iconibus cx Ilustratum. Post obitum auctoris opus inchoatum absolvit, correxit, interpolavit Jo. Gottlob Schneider, Saxo. Berolini. Sumtibus Auctoris Impressum et Bibliopolio Sanderiano Commissum. i-lx + 1-584.