Cetostoma now links to Eurpharynx in the LRT

Again, obvious in hindsight,
the pink flabby whalefish, Cetostoma (Fig 1), now nests closer to the gulper eel Eurypharynx (Fig 1) in the large reptile tree (LRT, 2338 taxa). The big difference, the size of the cranium vs the mandibles, was probably what kept these two apart until now.

Several relatives (Fig 1) experimented with variations in cranium sizes between these two extreme eel-like taxa.

Figure 1. The gulper eel, Eurypharnyx, has a tiny cranium and what seem to be oversize jaws. This compares to the whalefish, Cetostoma, which has a cranium more in keeping with the relative size of its jaws. Here they are shown together alongside several relatives. ” data-image-caption=”

Figure 1. The gulper eel, Eurypharnyx, has a tiny cranium and what seem to be oversize jaws. This compares to the whalefish, Cetostoma, which has a cranium more in keeping with the relative size of its jaws. Here they are shown together alongside several relatives.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/06/eurypharynx-cetostoma588.jpg?w=63″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/06/eurypharynx-cetostoma588.jpg?w=214″ class=”size-full wp-image-93340″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/06/eurypharynx-cetostoma588.jpg” alt=”Figure 1. The gulper eel, Eurypharnyx, has a tiny cranium and what seem to be oversize jaws. This compares to the whalefish, Cetostoma, which has a cranium more in keeping with the relative size of its jaws. Here they are shown together alongside several relatives. ” width=”584″ height=”2789″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/06/eurypharynx-cetostoma588.jpg?w=584&h=2789 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/06/eurypharynx-cetostoma588.jpg?w=63&h=300 63w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/06/eurypharynx-cetostoma588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />

Figure 1. The gulper eel, Eurypharnyx, has a tiny cranium and what seem to be oversize jaws. This compares to the whalefish, Cetostoma, which has a cranium more in keeping with the relative size of its jaws. Here they are shown together alongside several relatives.

Not only phylogenetically, but ontogenetically and sexually
whalefish (Cetostoma) go through a metamorphosis = change of shape. According to Johnson et al 2009, “We resolve a long-standing biological and taxonomic conundrum by documenting the most extreme example of ontogenetic metamorphoses
and sexual dimorphism in vertebrates. Based on morphology and mitogenomic
sequence data, we show that fishes currently assigned to three families with greatly differing morphologies, Mirapinnidae (tapetails), Megalomycteridae (bignose fishes) and Cetomimidae (whalefishes), are larvae, males and females, respectively, of a single family Cetomimidae. Morphological transformations involve dramatic changes in the skeleton, most spectacularly in the head, and are correlated with distinctly different feeding mechanisms. Larvae have small, upturned mouths and gorge on copepods. Females have huge gapes with long, horizontal jaws and specialized gill arches allowing them to capture larger prey. Males cease feeding, lose their stomach and oesophagus, and apparently convert the energy from the bolus of copepods found in all transforming males to a massive liver that supports them throughout adult life.”

Cetostoma regani
(Zugmayer 1914, 24cm) is the deep sea pink flabby whalefish.

Eurypharynx pelecanoides
(= Gastrostomus Vailiant 1882; up to 75cm long) is the extant deep sea pelican eel or gulper eel. Like its sister, the moray eel, the naris, antorbital fenestra, orbit and temporal fenestra are confluent. Both lack fins. Distinctly the jaw joint is far behind the occiput and hyperelongated hyomandibular and quadrate. The stomach can stretch to accomodate large prey. The muscle segments are V-shaped, not W-shaped. The lateral line system projects from the body, rather than lying in a groove.

References
Johnson GD et al (6 co-authors) 2009. Deep-sea mystery solved: astonishing larval transformations and extremed sexual dimorphisim unit three fish families. Biology Letters 5:235–239.
Valliant LL 1882. Sur un poisson des grandes profondeurs de l’Atlantique, l’Eurypharynx pelecanoides. Comptes Rendus Hebdomadaires des Séances de l’Académie des Sciences, Série D, Sciences Naturelles 95: 1226-1228.
Zugmayer E 1914. Diagnoses de quelques poissons nouveaux provenant des campagnes du yacht Hirondelle II (1911-1913). Bulletin de l’Institut Océanographique (Monaco). No. 288: 1-4.

wiki/Eurypharynx
wiki/Cetostoma – pink flabby whalefish