Pseudoliparis: the deepest fish in the world

Updated January 10, 2021
with the addition of the Atlantic cod, Gadus, these taxa now nest with it.

This is what happens
to your body when you live 8000m below the surface of the sea, the Mariana Trench.

Figure 1. Pseudoliparis in vivo and in µCt scans. Note the reduction of skull bones. Compare to Liparis in figure 2.

Figure 1. Pseudoliparis in vivo and in µCt scans. Note the reduction of skull bones. Compare to Liparis in figure 2.

Derived from ancestors from the shallowest of tide pools,
Pseudoliparis swirei (Gerringer et al. 2017; 28cm; USNM 438975 / HADES 200060; Fig. 1) is the extant Mariana snailfish. It lives in the deepest (8000m) ocean trenches. Note the reduction of the skull bones to mere struts as compared to Liparis (Fig. 2).

Andriashev and Pitruk (1993) define the genus 
Pseudoliparis as having “a well-developed disk and one pair of nostrils and lacking pseudobranchia and pleural ribs, with four radials in the pectoral girdle, which has neither notches nor fenestrae.” Pseudoliparis eats crustaceans and has 1cm eggs.

Figure 2. Liparis skull from the OSF website. Colorized here using tetrapod homolog colors.

Figure 2. Liparis skull from the OSF website. Colorized here using tetrapod homolog colors.

Pseudoliparis was not added
to the large reptile tree (LRT, 1791+ taxa), but its shallow pond sister Liparis (Figs. 2, 3) with a more ossified skull was added to the LRT. Both are derived from a sister to the cod, Gadus (Fig. 4).

Figure 3. Liparis florae in vivo.

Figure 3. Liparis florae in vivo.

Liparis florae (Linneaus 1766, Scopoli 1777) is the extant tidepool snailfish, a member of the Scorpaeniformes. Here it nests with Gadus. The postorbital detaches from the postfrontal and creates a cheekbone, analogous to the zygomatic arch of mammals.

Figure 4. Skull of the Atlantic cod, Gadus. Note the posterior process of the hyomandibular (dark green).

Figure 4. Skull of the Atlantic cod, Gadus. Note the posterior process of the hyomandibular (dark green).

Figure 5. Atlantic cod, Gadus morhua, in lateral view.

Figure 5. Atlantic cod, Gadus morhua, in lateral view.

Gadus morhua (Linneaus 1758) is the Atlantic cod, nesting between Scorpis and Perca. The anal fin is split in two. The chin has a barbel. The postparietal forms a long crest that divides the parietal. The naris is divided in two by the lacrimal. An antnarial opening precedes the naris. Note the elongate intertemporal and hyomandibular.


References
Gerringer ME, et al. 2017. Pseudoliparis swirei sp. nov.: A newly-discovered hadal snailfish (Scorpaeniformes: Liparidae) from the Mariana Trench”. Zootaxa. 4358 (1): 161–177.
Girard CF 1858. Notes upon various new genera and new species of fishes, in the museum of the Smithsonian Institution, and collected in connection with the United States and Mexican boundary survey: Major William Emory, Commissioner. Proceedings of the Academy of Natural Sciences of Philadelphia. 10: 167-171.
Linnaeus C von 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.
Linneaus C von 1766. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio duodecima, reformata. pp. 1–532. Holmiæ. (Salvius).
Scopoli JA 1777 [ref. 3990]. Introductio ad historiam naturalem, sistens genera lapidum, plantarum et animalium hactenus detecta, caracteribus essentialibus donata, in tribus divisa, subinde ad leges naturae. Prague. i–x + 1–506.

wiki/Liparis
wiki/Gadus_Atlantic_cod
wiki/Pseudoliparis

Cornell University Museum of Vertebrates
Liparis
skull, OFS website:
https://osf.io/5gxr6/wiki/home/  

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