The outer skeleton of the foraminifera Spiculosiphon oceana is formed by silica spicules of dead sponges glued together with organic matter. The organism is a hollow petiole 4 cm long and 0.5 cm in diameter, consisting of long and thin spicules neatly fitted together, glued to each other parallel to the petiole axis. Another representative of the genus Spiculosiphon , Spiculosiphon radiata , is half the size and is found in Norway . Spiculosiphon oceana is a real giant of the world of unicellular organisms , the largest species of foraminifera in the Mediterranean [1] [2] . The end of the petiole is closed and slightly swollen into the bulbous structure, which is not permanently attached to the substrate. The other end of the petiole is a hollow spherical structure containing the main part of the protoplasm and reaching a diameter of 1.2-1.8 mm. It is composed of spicules sparsely spaced, separated by irregularly shaped gaps so that pseudopodia can pass through it. The spherical part forms long and thin outgrowths-spicules that do not branch and form a crown with a diameter of 4 mm. They also provide structural support for pseudopods protruding into the water. The outgrowths are arranged so that the contact area of the pseudopods trapping food particles and water is largest. Spiculosiphon oceana lie on its side, not firmly attached to the substrate, and releases pseudopodia, which serve to capture plankton [3] . Thus, the structure and lifestyle of Spiculosiphon oceana are very similar to the organization of carnivorous sponges, so it can be concluded that the two groups converge [1] . Moreover, initially this type of foraminifera was mistaken for a sponge [4] .
Scanning electron microscopy of the petiole
Spiculosiphon oceana In addition to the species Spiculosiphon oceana , the genus Spiculosiphon includes the species Spiculosiphon radiata , found in sand collected from the bottom in the waters of northern Norway . Morphologically, both species are similar to each other, but there are differences between them. The hollow stalk of S. oceana is almost twice as large as the petiole in S. radiata and forms a closed bulbous extension at the proximal end. In addition, thin radial spicules emerging from the distal spherical expansion of S. oceana are not divided into thinner branches, unlike S. radiata spicules [1] .
The species Spiculosiphon oceana was discovered in caves near the seamount Seco de Palos, located 48 km southeast of Spain . This is the first representative of the genus Spiculosiphon , described in the Mediterranean. Interestingly, predatory sponges were first discovered in the same caves [2] . The species epithet is given in honor of the non-profit group , which opened the view with the Centro de Estudios Avanzados de Blanes (CEAB-CSIC) [1] . The holotype and paratype of the species are kept at the National Museum of Natural Sciences in Madrid [2] .
In 2014, the species Spiculosiphon oceana was included in the list of “ Ten most remarkable species ” by the [3] .
