The (Sea) Devil is in the Details

While anglerfishes are recognized for having unique features, the most well-known attribute pertains to the natural tool many of the fishes use for feeding. This tool is a modified dorsal spine that forms a lure and is used to attract prey. It is common among many varieties of Lophiiformes, like Ceratioids, but is not identical from one species to another.

Fig. 1 The angling fish can look quite different from each other (http://tinyurl.com/kcbhj3t)

Ceratioids, or seadevils, are widely recognized due to a combination of their luminescent angling lures, black skin pigment, and fang-like depressible teeth (Anderson and Leslie, 2001). 

Fig. 2 Deep-sea ceratioid anglerfish (http://tinyurl.com/klnpl9o)

The lure is not a trait exclusive to Ceratioids, as it is found in most of the living 323 Lophiiform species, but within the Ceratioids, males lack the luring apparatus (Quigley, 2014). In addition to the lack of a lure, males also lose their normal jaw teeth during metamorphosis, and instead develop a set of denticles to grasp onto prospective mates (Quigley, 2014).  The males are obligatory sexual parasites (Anderson and Leslie, 2001) with well-developed large eyes, and oversized nostrils that aid in detecting potential mates through recognition of a species-specific chemical attractant emitted by females (Quigley, 2014). Ceratioid fishes are noted for their sexual dimorphism, with males displaying dwarfism, a denticular apparatus, an absence of specific traits, and total structural reorganization (M.P. et al., 2016). The strong differences between the two genders make Ceratioids easily distinguishable from their bottom-living Lophiiform relatives, like Lophius piscatorius (Quigley, 2014).

Fig. 3 Longray Seadevil, Ceratias holboelli (http://tinyurl.com/kdfw3yr)

The adaptations of Ceratioids have allowed the anglerfishes to survive in various waters, with sightings recorded in all oceans to both subpolar regions (Anderson and Leslie, 2001) and just one sole finding in Russian waters (Kharin and Milovankin, 2007). Due to their relative abundance, high species diversity, and trophic position as top primary carnivores, ceratioid anglerfishes hold high ecological importance (Quigley, 2014). 
Although they are not the most commonly discussed of the anglerfishes, seadevils clearly have an array of noteworthy features that separate them from similar fishes, and aid in their survival. Not only are Ceratioidei hardly limited by water conditions, but their reproductive strategies transform their ability to survive into an ability to thrive.

References

      Anderson, M. and Leslie, R. (2001). Review of the Deep-Sea Anglerfishes (Lophiiformes: Ceratioidei) of Southern Africa. Ichthyological Bulletin, [online] 70, pp.1-29. Available at: http://bit.ly/2qzoUIt [Accessed 18 Apr. 2017].

      Kharin, V. and Milovankin, P. (2007). A new occurrence of the Deepsea Anglerfish Cryptopsaras couesii (Osteichthys: Lophiiphormes: Ceratiidae) in Russian waters. Journal of Ichthyology, [online] 47(1), pp.112-113. Available at: http://bit.ly/2pSyHx7

      M. P., R., Jacob, V., K. S., S., V. N., S., M., H. and M., S. (2016). Three new records of rare deep-sea Anglerfishes (Lophiiformes: Ceratioidei) from the Northern Indian Ocean. Marine Biodiversity, [online] 46(4), pp.923-928. Available at: http://bit.ly/2qyZNW4 [Accessed 18 Apr. 2017].

      Quigley, D. (2014). Ceratioid Anglerfishes (Lophiiformes: Ceratioidei) in Irish Waters. Sherkin Comment, [online] (58), p.7. Available at: http://bit.ly/2p3YuOD [Accessed 18 Apr. 2017].

      Fig. 1: Pietsch, T. (2013). The angling fish can look quite different from each other. [image] Available at: https://m.simplyscience.ch/kids-tiere-pflanzen/articles/auf-tauchstation-24659.html [Accessed 18 Apr. 2017]. http://tinyurl.com/kcbhj3t

      Fig. 2: Luminescent Labs (2013). Deep-sea ceratioid anglerfish. [image] Available at: http://blog.luminescentlabs.org/post/61812091341/deep-sea-ceratioid-anglerfish-this-beautiful [Accessed 18 Apr. 2017].

      Fig. 3: Bray, D. (2017). Longray Seadevil, Ceratias holboelli. [image] Available at: http://fishesofaustralia.net.au/home/family/180 [Accessed 18 Apr. 2017].