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Dragonfish

The deep sea dragonfish is a ferocious predator in spite of its small size. Dragonfishes are primarily mesopelagic, meaning that most inhabit Open Ocean waters about 1000 to 3000 meters deep, although some come to the surface at night to feed and others stay in waters as deep as 5000 meters. Plants do not live at these depths; so all dragonfishes are predators on other marine fishes and deep-water invertebrates.

Among the specializations of dragonfishes are very large hinged teeth, light organs on a barbell, a fleshy extension from the lower jaw, and/or on the pectoral fins, and in some species modifications that resemble a spring on the anterior portions of the backbone. In addition, most dragonfishes have small light organs, some forming lines, along the body. The feeding apparatus of these sea animals is well developed, but the rest of the body is less so, and reduced skeletons and musculature are specializations associated with the low energy budget of the mesopelagic environment.

Dragonfish is especially noteworthy because of the pectoral fin is highly modified to carry an elaborate light organ. It is otherwise one of the most morphologically primitive members of the group. It occurs in the Atlantic Ocean from approximately 20�N to 45�N. Most dragonfishes have been captured above 1300 meters.

The skeleton of dragonfish is a lightly mineralized, with the exception of the jaws and other portion of the feeding apparatus, which are the most distinctive features of the scan. These bones include the premaxilla and maxilla of the upper jaws and the dentary and anguloarticular of the lower jaw. In addition, the major bones that support or reinforce the jaws, including the hyomandibula and preopercle, are easily visible. The pectoral girdle bones, which are used both in locomotion and feeding, are also well developed, including the post temporal and cleithrum.

The jaw teeth of dragonfish are large and recurved. Some are tightly bound to the jawbones, while others are hinged, allowing them to tilt back when prey are pulled backwards towards the gullet. Like most other fishes, dragonfish has a "second" set of jaws deep in the oral cavity on certain bones of the branchial basket, and these are clearly visible in the scan. The branchial basket carries the gills as well as teeth, and serves several important functions in the life of the individual. Some of the bones of this basket can be seen in the scan, mostly as small fragments distributed in the oral cavity.

Most of the braincase is cartilage and not visible in the scan; the bones surrounding the brain are very thin and lightly mineralized so are not clearly visible or do not appear at all. The vertebral column is clearly visible in the specimen. Perhaps less obvious is the fact that the anterior centra are smaller and slightly less mineralized than those more posterior. In most stomiids, the anterior centra are either very lightly mineralized or not present at all, leaving the prominent notochord as the major support between the head and postcranial body. Also visible are the small, multi-branched intermuscular bones behind the head and along the vertebral column. These bones lie in the muscles of the body and serve as anchors for them.

The pectoral fins are visible, as are some of the small bones, the pectoral radials, which support and connect them with the pectoral girdle. Dragonfish has unique pectoral radials, associated with the specialized morphology of the fins.

Other distinctive features of the scan are the eye lenses, which are composed of dense proteins and the otoliths (ear stones), which are densely mineralized structures used in hearing and balance.

Black Dragonfish

The black dragonfishes (Family Idiacanthidae) are long, slender fishes, which live in marine waters down to about 1000m deep. These fishes are sexually dimorphic (the males and females look different). The female has small eyes, long fang-like teeth, and chin barbel. The male is much smaller (5cm maximum length vs 40cm for the female) it lacks teeth, lacks the chin barbel, has a non-functional gut, and is dark brown rather than black. It appears that the male's main role is reproduction.

Like many deepsea fishes, the Black Dragonfish can produce its own light. This species has tiny photophores (light producing organs) scattered over its body and two rows of larger photophores along the side of the body. The chin barbel of the female also has a slender luminous tip. This may be used to attract prey.

Larval black dragonfishes are most unusual. They are long, slender, transparent fishes that have their eyes at the ends of long stalks, which can be up to half the length of the body.