Within the phylum Mollusca, class Gastropoda, order Aplysiida, family Aplysiidae and genus Aplysia, we find the black sea hare or Aplysia fasciata. It is a species that inhabits the shallow waters (2-20 meters) of both the western and eastern Atlantic Ocean, as well as the Mediterranean Sea.
Aplysia fasciata can reach a maximum total length of 40 cm, making it one of the largest species of sea hares, which can reach a weight of 1.5 kg. Its body has a homogeneous black or dark brown color, with some specimens having a red-orange line bordering its appendages. There is a certain degree of chromatic and pattern variability, with some authors considering that the species Aplysia brasiliana present in the western Atlantic Ocean, is actually a color variant of Aplysia fasciata. Some specimens have the body covered by whitish spots. From the body structure, we can distinguish two oral tentacles in the anterior region of the body, as well as two rhinophores located slightly further back and at the base of which we find the eyes. Behind the rhinophores, and running along the entire body, we find on each side the parapods, flattened appendages, which are sometimes used by the specimens to swim thanks to their undulating movements. Inside the body of Aplysia fasciata specimens we find a shell that is not very developed but can reach up to 7 cm in length.
During the day, Aplysia fasciata specimens are usually not very active, and often cover their body with the parapods as a blanket. It is during the night when specimens of this species are most active, tirelessly searching for algae to feed on, especially algae of the genera Ulva, Enteromorpha, Jania, Pterocladia and Laurentia.
It has the ability to release an ink-like substance, purple in color, which despite not being toxic, is used to mislead attacks of potential predators.
During the reproductive season, which takes place at the end of summer, they deposit cream-colored gelatinous masses inside which we find the clutch. It is a simultaneous hermaphrodite species, and is often observed during this reproductive season forming small groups of invidivores placed in a row.
There is the possibility of confusing specimens of Aplysia fasciata with Aplysia punctata. The latter is somewhat smaller (maximum 7 cm in length) and never has the edges of its extremities (parapods, rhinophores and / or oral tentacles) with red edges, something that can occur in some specimens of Aplysia fasciata.
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