[Animals] The sheep-faced sea slug that 'photosynthesises'

[#Wittels-]

These curious sheep-faced sea slugs get energy from the sun, just like plants do. Their trick: they don't digest the chloroplasts of the algae they feed on, which allows them to take advantage of the photosynthetic process and thus get extra energy

Sea slugs are extraordinarily biodiverse animals, so it is very common to find very unique species. Among them is Costasiella Kuroshimae, a gastropod mollusk measuring just over 10 millimeters that is causing a sensation on social media due to its more than reasonable resemblance to a sheep. So much so that in English it is known by the nickname of 'sea sheep'. It was discovered in 1993 off the coast of the island of Kuroshima, in Japan, although it has also been located in the waters of the Philippines and Indonesia. But, beyond their appearance, the most curious thing about these marine creatures is their way of getting the most out of the algae they feed on on the seabed, with which they maintain a very particular symbiotic relationship.

The bumps on these slugs' heads are not sheep's horns, but 'rhinophores', a sensory organ of prosobranch mollusks that serve as chemical sensors.

In nature there are numerous examples of symbiotic relationships between organisms of different species: in most cases both species help to reduce each other, but on some occasions one of them takes advantage of the other, which is known as kleptoplasty. An example of this process can be found in the sacoglossus, some gastropod molluscs from the group of opisthobranchs to which this sea slug with a face similar to a sheep belongs.

It turns out that when these slugs ingest algae, they do not digest the chloroplasts, the organelles that algae and plants have and that are used to carry out photosynthesis, but rather 'reserve' them inside, so that they continue to perform their function. In this way, these sea slugs can not only feed on the content of the algae, but also take advantage of the sugars manufactured by the chloroplasts that they maintain in their organism, which provides them with a very useful alternative source of food to grow and reproduce in an environment with very few resources. Although these slugs aren't particularly good at photosynthesis, some species can live for months feeding on chloroplast activity alone.

Another of the particularities of these organisms are the protuberances similar to ears that they have on their heads. Although they look like the characteristics of sheep's ears, they are rhinophores, chemical sensors that many sea slugs have and use as taste receptors. These small filaments allow these organisms to scrutinize the chemical elements present in the water in search of food, or a partner, although they practically do not need it, since they are hermaphrodites. Once reproduction begins, they will lay between 2,000 and 4,000 eggs that hatch after about 4 days, giving rise to larvae that will soon acquire that characteristic sheep shape.

 

Link: https://www.nationalgeographic.com.es/mundo-animal/estas-babosas-marinas-cara-oveja-hacen-fotosintesis_19773