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Rays (Myliobatidae and Mobulidae)
Manta Ray Manta birostris (Walbaum, 1792)
Rays are characterized by their flattened form. The enlarged laterally expanded pectoral fins are fused with the body to form the disk; the five (rarely six) pairs of gill openings are ventral on the disk. Respiratory water is taken into the spiracles (an opening behind each eye) and passed out the gill openings.
The mouth is ventral, the teeth generally flat and pavement-like. The rays share many of the general features listed for sharks. Seven different families of rays are known to have a long venomous spine or spines on their tail bearing numerous small barbs on each side. The pain from wounds delivered by these spines is excruciating; deaths have been reported. Immediate soaking of a wounded limb in water as hot as can be endured helps to alleviate the pain.
Rays often bury in the sand or mud with only their eyes and spiracles showing. They feed mainly on shellfish and worms, and occasionally on small burrowing fishes that they excavate from the sediment. Rays are ovoviviparous; the nutrition for the developing eggs is initially from yolk, but later from albuminous fluid
The eagle rays have the head distinct from the disk, with the eyes oriented more laterally than dorsally; the disc is at least 1.6 times broader than long, the outer corners acutely pointed; the tail is long and whip-like with a small dorsal fin near the base; one to several venomous spines may be present on the basal part of the tail.
The teeth are flat, plate-like, and hexagonal. Eagle rays feed mainly on hard-shelled mollusks and crustaceans. The mollusk shells are crushed in the powerful jaws, and the shell fragments ejected from the mouth. The Spotted Eagleray is the only representative of the family in Hawaiian waters.
Manta Rays (Mobulidae)
This family consists of two genera, Mobula (common name, devilfishes) with nine species in the world (only a single record from Hawaii), and Manta with an unknown number.
Although many believe there is more than one kind of manta, most authors are conservative and recognize only the single species illustrated below.
Mantas and devilfishes feed on zooplankton, hence are not bottom dwelling. Like their relatives the eaglerays, they have a disk that is much wider than long, with pointed tips; the head is broad, with a pair of unique cephalic flaps, one on each side at the front, which are used to direct food organisms into the mouth; the flaps are coiled into a tight spiral when not feeding.
Aetobatis narinari (Euphrasen, 1790) Hihimanu
Disk dark gray to black dorsally with white spots or rings, its width 1.7-1.8 times the length; tail very long,as much as 3 times disk width, with one to five venomous spines near its base.
Largest recorded, 7.5 feet (230 cm) in width. Cosmopolitan in warm seas .Very active; sometimes leaps free of the surface.
Mantas bisrostris (Walbaum, 1792) Hahalua
Dark gray to black dorsally, sometimes with whitish areas, and white ventrally, often with dark blotches; disk 2.2 times wider than long. Reported to a width of 23 feet (7 m).
Occurs in all tropical and subtropical seas (if there is but one species of the genus). Often accompanied by the remora Remorina albescens.
All information and pictures in this section are from John E. Randall's Shore Fishes of Hawai'i by permission of the author.
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