The undulate ray or Raja undulata has a very flattened body with a diamond shape and a short face. The dorsal surface of the disk has dark sinuous lines and a multitude of white spots of different sizes on a background of variable color between brown, yellowish or gray. Due to this coloration, Raja undulata goes unnoticed over the habitats where we can find it, rocky and sandy bottoms in which it buries its body leaving only the eyes and spiracles out to the surface. They can reach 100 cm in length, and usually 2-4 kg in weight.
Male individuals present numerous spiculations (20-55) in the middle of the body forming a row that begins in the area behind the eyes, and ends at the level of the first dorsal fin, following the dorsal line. The females also present spiculations, but these form 3 rows. At the top of the head, and located slightly to the side, we find the eyes. These are of a medium size, and immediately behind them we find the 2 spiracles. On the ventral surface, we find the mouth that adopts a slightly arched shape. Behind the mouth and laterally to it, we find 5 gill openings that are of moderate size. Finally, at the back of the body, we find the tail, whose size is similar to the size of the body. In it we find two dorsal fins located in a fairly terminal position with respect to the tail.
Raja undulata inhabits waters of the western Mediterranean Sea and eastern Atlantic (from the Irish coast to the Canary Islands) where it feeds during its juvenile stages on benthic organisms such as polychaete, echinoderms, crustaceans, molluscs and small fish, and later, when they become mature individuals, they go on a diet that is practically exclusive of crustaceans.
The reproduction of Raja undulata is oviparous, reaching sexual maturity at 7-9 years (its estimated maximum age is around 20 years). Each female, during the months of March to June, is capable of laying up to 20 eggs wrapped in a horny capsule of rectangular shape and with some extensions in the vertices of about 10-15 cm which allow the egg to cling to the seabed. The incubation of the eggs is about 4-5 months, after which a fully formed individual emerges.Photos: