Thursday, August 18, 2011

[Ichthyology • 2011] Protoanguilla palau • A 'living fossil' eel (Anguilliformes: Protoanguillidae, fam. nov.) from an undersea cave in Palau

Protoanguilla palau
Johnson, Ida, Sakaue, Sado, Asahida & Miya, 2011

We report the discovery of an enigmatic, small eel-like fish from a 35 m-deep fringing-reef cave in the western Pacific Ocean Republic of Palau that exhibits an unusual suite of morphological characters. Many of these uniquely characterize the Recent members of the 19 families comprising the elopomorph order Anguilliformes, the true eels. Others are found among anguilliforms only in the Cretaceous fossils, and still others are primitive with respect to both Recent and fossil eels. Thus, morphological evidence explicitly places it as the most basal lineage (i.e. the sister group of extant anguilliforms). Phylogenetic analysis and divergence time estimation based on whole mitogenome sequences from various actinopterygians, including representatives of all eel families, demonstrate that this fish represents one of the most basal, independent lineages of the true eels, with a long evolutionary history comparable to that of the entire Anguilliformes (approx. 200 Myr). Such a long, independent evolutionary history dating back to the early Mesozoic and a retention of primitive morphological features (e.g. the presence of a premaxilla, metapterygoid, free symplectic, gill rakers, pseudobranch and distinct caudal fin rays) warrant recognition of this species as a ‘living fossil’ of the true eels, herein described as Protoanguilla palau genus et species nov. in the new family Protoanguillidae.

Keywords: eel; morphology; phylogeny; new species, genus and family; divergence time

Figure 1. Protoanguilla palau. (a) Holotype, NSMT-P 98249 female, 176 mm SL. (b–g) Paratype USNM 396016 juvenile, 65 mm SL: (b) whole specimen; (c,d) head in lateral and ventral view, respectively; (e) close-up of tubular gill opening, left side in ventral view; (f) alizarin red-stained body scales along lateral midline (lateral-line scales are forming in alcian blue-stained areas); (g) USNM 396051, 150 mm SL, alizarin red-stained, close-up of lace-like, tubular lateral-line scale.

Protoanguilla palau

• A primitive-looking eel from an undersea cave in Palau retains ancient Dinosaur-Era features.
• Since the eel's history goes back 200 million years, with few bodily changes occurring over that time, scientists refer to it as a "living fossil."
• The eel's only known habitat is the Palau cave, so it could be highly endangered.

Johnson, G. D.; Ida H., Sakaue J., Sado T., Asahida T. & Miya M. (2011). "A 'living fossil' eel (Anguilliformes: Protoanguillidae, fam nov) from an undersea cave in Palau". Proceedings of the Royal Society B (in press). doi: Retrieved 17 August 2011.

• 'Living Fossil' Retains Dinosaur-Era Look : Discovery News
• 'Fossil eel' squirms into the record books
• New species of dinosaur-era eel wriggles into history books as a 'living fossil':