Clathrina clathrus or also known as yellow clathrina, is a sponge of the family Clathrinidae within the class Calcarea. It inhabits the waters of the Mediterranean Sea and the eastern Atlantic Ocean, from the Canary Islands to the coasts of the United Kingdom. Generally, we will find this species in shallow waters (3 - 30 meters), with few currents and always in shady places (south facing), usually cave entrances or vertical walls.
The body of Clathrina clathrus consists of a mass of tubes between 0.5 and 3 millimeters in diameter, which are interconnected with each other forming a dense network. The total size of the specimen can reach 10 cm in diameter. It is a translucent sponge whose color is bright yellow, although there are specimens that can be whitish. A characteristic of Clathrina clathrus, although of little relevance if we do not have a microscope, is that in the tubes that make up its body, we will find calcareous spicules in the shape of 3-pointed stars.
Like all sponges, the feeding of Clathrina clathrus is based on the filtration of water through a multitude of small pores present throughout its body. From the water it takes the organic particles and expels the water through larger orifices that are generally present in the upper part of the body.
As for the reproduction of Clathrina clathrus, it is a hermaphrodite species, and therefore they generate both eggs and sperm in the same specimen. During the months between November and February, they release their spermatozoa into the water, which travel with the currents. If one of them is captured by another specimen of the same species through its inhalant pores, the sperm will internally fertilize the ovule. This generates a larva that is expelled from the body of the specimen and will remain swimming freely in the plankton for several weeks. After this period, the larva will settle on the bottom to generate a new specimen of Clathrina clathrus.
There is a possibility of confusing Clathrina clathrus with a close relative, the species Clathrina contorta. Their color and shape are similar. In order to differentiate them, we will have to focus on the thickness of the tubes that make up the body. In the case of Clathrina contorta these tubes are thinner and with a more rigid aspect than the tubes of Clathrina clathrus.
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