About Diplobatis ommata (Jordan & Gilbert, 1890)
This is the ocellated electric ray, with the scientific name Diplobatis ommata (Jordan & Gilbert, 1890).
Its pectoral fin disc is heart- or trowel-shaped and slightly wider than it is long. A pair of large, kidney-shaped electric organs are visible through the skin on either side of the head. Small eyes are followed by even smaller spiracles, which have seven to ten small, rounded projections along their rims. The snout is broadly rounded, and each nostril is split into two openings by a strut. A curtain of skin with a smooth to gently wavy posterior margin sits between the two nostrils. The small mouth forms a transverse line; the lower jaw edge is scalloped, and when the mouth is closed, it usually conceals the teeth. There are 14 to 16 tooth rows in each jaw. The small, pointed teeth get progressively longer and sharper toward the back of the jaw, and are arranged in a quincunx pattern. Five pairs of small gill slits are located on the underside of the disc. Large pelvic fins originate underneath the disc, and have convex trailing margins. Adult males have very short, thick claspers. The broad, flattened tail is shorter than the disc, and carries a fold of skin along each side. There are two small dorsal fins, both with rounded to angular apices; the first dorsal fin is slightly smaller than the second, and its position varies from over the pelvic fins to behind them. The caudal fin is triangular with rounded corners, and is roughly symmetrical above and below. The skin is soft and completely lacks dermal denticles.
The dorsal coloration of the ocellated electric ray is extremely variable, with the only consistent feature being the large ocellus ("eyespot") in the middle of its back. The center of the ocellus is black or yellow, and is surrounded by concentric, alternating dark and light rings that can be either continuous or broken. The rest of the upper surface is most commonly a shade of light brown with numerous fine dark dots; it may also have light dots, larger dark spots or blotches, and/or irregular brown marbling. Some individuals are plain light or dark brown with a black ocellus. The section of the disc in front of the eyes is brown, with up to five darker blotches. The dorsal pattern often extends to the ventral fin margins; the rest of the underside is white to cream-colored. This species can grow up to 25 cm (9.8 in) long.
The ocellated electric ray is common in the tropical coastal waters of the eastern Pacific. Its range extends north to the Gulf of California and Bahía San Juanico in Baja California Sur, and south as far as Ecuador. It is a bottom-dwelling species, recorded from the intertidal zone down to a depth of 94 m (308 ft). Its favored habitat is sandy bays, though it can also be found over rubble bottoms, rocky terrain, and rhodolith beds.
Like other members of its family, the ocellated electric ray can defend itself by producing a moderate electric shock. During the day, this solitary ray spends most of its time lying partially buried in sand, often near rocky reefs. It becomes more active at night, using its pelvic fins to "hop" along the sea floor. It feeds on small crustaceans such as amphipods and shrimp, as well as polychaete worms. Documented parasites of this species include the tapeworms Acanthobothrium dollyae, A. maryanskii, and A. royi, and the fluke Anaporrhutum euzeti. While specific reproductive details are unknown, the ocellated electric ray is presumed to be viviparous: like other electric rays, developing embryos are first sustained by yolk, and later by maternally produced histotroph ("uterine milk"). Females reach sexual maturity at under 19 cm (7.5 in) long; the size at maturation for males is unknown.
