‘Enigmatic’ Polymixia, the beardfish, enters the LRT alongside ‘enigmatic’ Anomalops, the flashlightfish

Essentially this is part 4
in the search for a flashlightfish (Fig. 2) sister. We’re getting closer and closer phylogenetically, still with no clue as to the origin of the flashlightfish’s unique flashlight.

That’s just the way
cladograms work or, at least, are supposed to work. See how adding taxa gets you closer and closer? By contrast, taxon omission never provides answers to traditional enigmas, no matter how many PhDs put their name on a paper. Character addition doesn’t help either. The LRT has enough characters to lump and split all included taxa. Adding taxa is how the LRT recovers sister taxa for traditional enigma taxa while others flounder and claim success with unrelated, by default, taxa.

Polymixiformes
“Few groups have shifted back and forth as frequently as this one” (Nelson, et al. 1916).

Figure 1. The beardfish, Polymixia, in vivo, x-ray and mandible elements in diagram.

Polymixia nobilis (Lowe 1836; Polymixia hollisterae Grande and Wilson 2021; 30cm) is the extant stout beardfish, a benthic taxon found below 800m. The hyoids produce the barbels. Grande and Wilson wrote: “An enigmatic fish genus” Here Polymixia nests between Sargocentron and Anomalops, two taxa not mentioned by Grande and Wilson 2021. Each of the circumorbital bones has a laterally projecting flange. So far, that is exclusive to his genus, but is it a clue to the origin of the blinking light organ? Not quite. The light organ lies within the orbit, within the space created by the circumorbital bones.

Figure 2. Anomalops, the flashlightfish.

Anomalops katoptron (Kner 1868; 35cm) is the extant splitfin flashlightfish, a type of jack. Anomalops has a light organ (filled with luminious symbiothic bacteria blinking 90x a minute by moving the cover) beneath the large eyeball. That’s how it detects its prey, zooplankton. Teeth are extremely tiny. Anomalops nests basal to the jack, Seriola.

References
Grande TC and Wilson MVH 2021. A New Cryptic Species of Polymixia (Teleostei, Acanthomorpha, Polymixiiformes, Polymixiidae) Revealed by Molecules and Morphology. Ichthyology & Herpetology 109, No. 2, 2021, 567–586.
Lowe RT 1836. Piscium Maderensium species quaedam novae, vel minus rite cognitae breviter descriptae, etc. Transactions of the Cambridge Philosophical Society 6: 195–202.
Nelson JS, Grane T and Wilson MVH 2016. Fishes of the World, 5th ed. 705pp. Wiley.

wiki/Splitfin_flashlightfish
wiki/Sargocentron
wiki/Polymixia_nobilis
wiki/Beardfish