stomiiformes

Deep-sea Hatchetfish (juvenile) - Argyropelecus olfersi

This bizarre fish commonly called Deep-sea Hatchetfish, and scientifically named Argyropelecus olfersi (Stomiiformes - Sternoptychidae), is a species of deep sea fish which live in depths up to 800 m, but during the night they rise to shallower water layers up to 100 m below the surface. As an adaptation to their bathypelagic life their body is laterally compressed, they have big tubular eyes directed dorsally, and on the ventral side a series of pigmented photophores (luminous organs) that emit bright flashes.

This species is known to occur in the North and South Atlantic Ocean, and the South Pacific Ocean. 

References: [1] - [2] - [3]

Photo credit: ©Solvin Zankl | Locality:

2

Half-naked Hatchetfish (Argyropelecus hemigymnus)

Also known as the short silver or spurred hatchetfish, the half-naked hatchetfish is a species of deep sea marine hatchetfish that inhabits the mesopelagic zone in oceans worldwide. Half-naked hatchetfish are opportunistic feeders and will feed on small fish and zooplankton (particularly copepods and ostracods). During the day they will ‘rest’ in the depths and will make daily migrations closer to the surface at night to feed.

Half-naked hatchetfish are sexually dimorphic with males having more developed olfactory organs than females.

Phylogeny

Animalia-Chordata-Actinopterygii-Stomiiformes-Sternoptychidae-Sternoptychinae-Agyropelecus-A.hemigymnus

Images: Robert Patzner and Edd48

2

Sloane’s Viperfish (Chauliodus sloani)

…is a species of dragonfish/viperfish found in most subtropical and tropical oceans worldwide. Like most viperfish this species is normally found in deep waters at around 8,000 ft deep. They are most noted for their impressive teeth which are the largest teeth in the animal kingdom relative to head size. The fish uses these spear-like teeth to impale its prey in a quick dash. To withstand the shock in this the viperfish has a vertebrae behind its head which acts as a shock absorber.

Phylogeny 

Animalia-Chordata-Actinopterygii-Stomiiformes-Stomiidae-Chauliodus sloani

Image Source(s)