Meiacanthus, a little venomous Western Pacific blenny enters the LRT with the much larger North Atlantic wolffish, also with dentary fangs

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Meiacanthus grammistes
(originally Blennechis grammistes Cuvier and Valenciennes 1836, Fig 1) is the striped poison-fang blenny. It lives in the warm Western Pacific and grows to 11cm in length. The lower jaw is notable for its large venomous upside-down saber teeth.

Figure 1. Meiacanthus grammistes, the fang blenny, in several views from the venomdoc.com. Colors added here. Note the packed needle medial premaxillary teeth framed by larger premaxillary fangs separated by a diastema for the large dentary fangs when the jaws are closed. Note the vestigial maxilla (greeen stripe).

According to Wikipedia,
“The venom consists of a neuropeptide also seen in cone snail venom, a lipase similar to the one used by certain species of scorpions and an opioid peptide. Blennies use it to stun predators. The venom reduces the blood pressure of the predator, relaxing its jaws so the blenny can escape.”

VenomDoc.com reports:
“Fang blennies are a particularly fascinating group to research as they have a venomous bite instead of venomous spines like other fish, such as stingrays. They deliver a venom that is quite different from that of venomous spined fish, in that is not pain inducing. This is because they are not using their venom to deter larger predators but rather in fights with similar sized fish for territory. Their opioid peptide rich venoms induce dizziness in their competitors, giving the fang blenny an athletic competitive edge. If their competitors are extremely dizzy and uncoordinated, this would also make them easy prey for a predator…. thus being permanently removed from the competition!”

When added to
the large reptile tree (LRT, 2192 taxa), Meiacanthus (Fig 1) nests with another blenny, the several times larger (1.5m) Anarhichas, the Atlantic wolfish (Figs 2, 3) on the other side of the planet, in cold polar waters. The wolffish is traditionally considered close to scorpionifish, but Wikipedia reports, “The Atlantic wolffish has retained the bodily form and general external characteristics of small blennies (Blennioidei).” That’s an phylogenetic conflict resolved by the LRT.

Figure 1. Skull of the wolffish, Anarhichas.
Figure 2. Skull of the wolffish, Anarhichas. Note the large dentary fangs and robust circumorbital ring as in Meiacanthus (figure 1). Here the cranium is uniqely pinched behind the orbits, similar to cynodont mammals. I can’t think of another tested fish in the LRT that does this.

Olson 2017 reported,
“Smith et al. (2016) found that of the roughly 2,500 known venomous fish species, only two genera deliver venom with their fangs, including the one-jawed eel (Monognathus), and the fang-tooth blenny (Meiacanthus).”

Gene studies by Olson 2017
nest Meiacanthus with Channa among tested taxa. That’s not too far off from the LRT results. Unfortunately, Olson also nests Anarhichas with Gasterosteus, the stickleback. That’s very far off from the LRT, which nests sticklebacks with pipefish and sea horses based on traits.

Figure 2. Anarhichas in vivo. Note the basic similarities between this cave dweller and its open seas cousin, Coryphaena (Fig. 1).
Figure 3. Anarhichas in vivo. At 1.5m, this is what happens to blennies that enter the Atliantic. This taxon is not venomous. Pelvic fins are lost.

This appears to be a novel hypothesis of interrelationships.
If not, please provide a citation so I can promote it here.

References
Cuvier G and Valenciennes A 1836. Histoire naturelle des poissons. Tome onzième. Livre treizième. De la famille des Mugiloïdes. Livre quatorzième. De la famille des Gobioïdes. v. 11: i-xx + 1-506 + 2 pp., Pls. 307-343. [Valenciennes authored volume. i-xv + 1-373 in Strasbourg edition.]
Olson E 2017. The evolution of fangs across ray-finned fishes (Actinopterygii). Culminating Projects in Biology. 22.https://repository.stcloudstate.edu/biol_etds/22

wiki/Meiacanthus_grammistes
wiki/Atlantic_wolffish
http://www.venomdoc.com/
The Sidney Morning Herald: Meet the fang blenny

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