Within the order of nudibranchs we find the Aeolidiidae family and within it the species Berghia coerulescens. It is a species that inhabits both the waters of the Mediterranean Sea and the eastern Atlantic Ocean, from the Canary Islands to Great Britain. We will find this nudibranch on rocky bottoms, among algae or under rocks in waters up to 20 meters deep.
The body of Berghia coerulescens can reach a maximum length of 4-7 cm and the color of the body is translucent whitish. In the head region there are two thin and elongated semi-transparent blue oral palps, with a more opaque base and an orange apical end. Behind them we find two rhinophores that are smooth at their bases, with numerous rounded warts and orange in almost all of its length; and ending in a whitish apex. Between the oral palps and rhinophores, we find in the head region, two elongated orange spots. Behind the cephalic region, the body of Berghia coerulescens is made up of several groups of cerata grouped every 8 to 10 appendages. These cerata are long and narrow in shape, with a striking bluish coloration and orange/yellowish apical tip. The posteriormost third of the body is free of cerata and is formed by a thin and elongated whitish tail. Below the dorsal part of the body of Berghia coerulescens, we find a relatively wide foot, pinkish in color and not always visible due to the length of the cerata that may cover it partially or completely.
As is common in many species of nudibranchs, Berghia coerulescens usually lives on the species on which it feeds, its main prey being various species of anemones and hydrozoans, such as those of the genus Aiptasia or the hydrozoan Eudendrium racemosum respectively.
As for the reproduction of Berghia coerulescens, this is a hermaphrodite species of cross reproduction, which during the months of March to May exchange sperm to fertilize the eggs. After that, each of the specimens will lay, forming a translucent white ribbon, that takes the form of a spiral of approximately 2-3 cm in outer diameter. Inside this ribbon, thousands of eggs will be visible.
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