Sixgill Rays

What Are Sixgill Rays?

Sixgill stingrays (Hexatrygonidae) are characterized by their six pairs of gill openings, which have gill arches with well-developed filaments. They are unique among rays in that their spiracles (respiratory openings) are closed with an external valve flap, rather than an internal valve. The spiracles are large and far behind the eyes. The snout is long and triangular, measuring over a third of the total disc length. The snout, which is confluent with the rest of the disc, is translucent, depressed (thin), and some investigators suggest that it may be used as an electroreceptive organ. The nostrils are set wide apart, as are the eyes. The mouth is broad and contains many small, blunt teeth. The disc is longer than it is wide, and has smooth skin with no denticles or thorns: “an unusually flabby ray.” Sixgill stingrays have no dorsal fin. They do have small pelvic fins and a long, low caudal fin that reaches the tip of the tail. The tail is short, slender, not whip-like, and bears one or two serrated stinging spines. These rays are brownish pink, with a pale snout and dark caudal fin. Adults can measure up to 2 m long.

Diversity

The family Hexatrygonidae consists of one genus containing only one species. These marine stingrays are unique in that they have six pairs of gill openings and six gill arches, rather than five. They also have a distinctive triangular long snout, confluent with the rest of the disc created by the pectoral fins. They have a functional sting, but no reports of negative effects on humans were found. Little information was found regarding Hexatrygonidae, but stingrays in general are viviparous, and carnivorous.

Where To Find Sixgill Rays

Sixgill stingrays live in the western Pacific from Hong Kong to Japan, and off the coast of South Africa. They are found near Australia over the continental slope.

Communication and Perception

Rays perceive and interact with their environment using sensory channels common to many vertebrates: sight, hearing, smell, taste, and touch. The electrical sensitivity of elasmobranchs seems to exceed that of most other animals. Elasmobranchs are equipped with ampullae of Lorenzini, electroreceptor organs that contain receptor cells and canals leading to pores in the animal’s skin. Sharks and rays can detect the electrical patterns created by nerve conduction, muscular contraction, and even the ionic difference between a body (i.e. of prey) and water. In lab experiments, rays changed their feeding location according to artificially induced changes in the electrical field around them. Other experiments have demonstrated that cartilaginous fishes use electrosensory information not only to locate prey, but also for orientation and navigation based on the electrical fields created by the interaction between water currents and the earth’s magnetic field. Although some rays can produce an electric shock to defend themselves or stun prey, members of the family Hexatrygonidae cannot. They are able, however, to inflict a venomous sting with their tail spine in defense.

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