Slope conger

Ariosoma prorigerum is a small deep-water conger of the family Congridae, known in English as the slope conger ^[1],[2]. Charles Gilbert described it in 1891 from material that the steamer Albatross collected in 1888 around Panama and the Galápagos Islands ^[3].

It lives close to the seabed at roughly 380 to 740 m depth and does not exceed 35 cm in length ^[2]. The IUCN assessed it in 2007 as Least Concern ^[4].

The genus name, Ariosoma, comes from two Greek words: ari, expressing strength or superiority, and soma, meaning body ^[2]. Gilbert described the species in 1891 under the genus Ophisoma, which is now regarded as a synonym of Ariosoma ^[3],[2].

It is a slender, elongate eel. In his original description Gilbert noted that the head is as long as the trunk; the body depth is one thirteenth of the total length ^[3]. The vent lies well forward, so the tail is much longer than the body, although less than twice as long ^[3].

The snout is long and sharp, with its soft tip projecting beyond the lower jaw by more than two thirds of the orbit length ^[3]. The jaws are broad and strong, and the gape reaches back to a vertical line through the rear edge of the pupil ^[3]. The teeth are fine and bristle-like, set in broad bands, and none is enlarged; behind the head of the vomer there is a transverse groove that receives the tip of the lower jaw ^[3]. The eye is small: half the snout length, going about 8 times into the head ^[3].

The colour is a uniform light brown. The fins are dusky and nearly black towards the tail tip, where they carry a very narrow white margin; the mouth, gill cavity and peritoneum are black ^[3]. The dorsal fin starts in front of the gill opening, and the pectoral fin is two sevenths of the head length ^[3].

Similar species

• Ariosoma balearicum: In Gilbert's key, that species has the vent near the middle of the body and a body and tail of similar length, whereas in Ariosoma prorigerum the vent is anterior and the tail is much longer than the body ^[3].

According to FishBase, the species lives in the eastern Pacific, with records from Costa Rica, Panama and Ecuador, between 10° N and 1° S ^[2]. Gilbert's type is a single individual taken at Albatross station 2792 in 401 fathoms (about 733 m); a second small specimen came from station 2799 ^[3].

It is a bathydemersal species, meaning it lives in deep water close to the bottom, over a depth range of 380 to 740 m ^[2]. The accepted classification places it in Chordata, Teleostei, Anguilliformes, Congridae, Ariosoma ^[1]. FishBase cautions that further studies are still needed to confirm that it belongs in that genus ^[2].

The IUCN assessed the species on 22 May 2007 and placed it in the global category Least Concern (LC) ^[4],[2]. The assessment was prepared by McCosker, Béarez, Bernal and Lea ^[4].

Not medical advice. For a sting, a poisoning or an allergy, seek medical care.

FishBase rates it as harmless to people ^[2].

According to FishBase, the species is of no interest to fisheries ^[2]. It is one of the eels that Gilbert described from the material of the Albatross expedition ^[3].