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Cetaceans (Cetacea Brisson, 1762) are an order of Eutherians mammals, completely adapted to the aquatic life. The cetacean name derives from the Greek κeτος (ketos), which means "whale" or "sea monster", and was introduced by Aristotle to designate aquatic animals endowed with pulmonary respiration.
They have a fusiform body, similar to that of fish, which ensures greater hydrodynamics. The forelimbs are modified in fins, while the hind limbs as such are absent: only a few small vestigial bones remain, hidden inside the body, and not connected to the spine due to the absence of the pelvis. The caudal fin is arranged horizontally and divided into two lobes. They are generally free of hair and are thermally insulated from a thick layer of fat.
The Cetacea order includes about 85 species, almost all marine species except 5 species of freshwater dolphins. The species are divided into two suborders: Mysticeti and Odontoceti. There is a third suborder, Archaeoceti, to which only extinct species belong.
Among the mysticetis there are the animals commonly called whales, the largest known in the world: in particular the blue whale is the largest animal on Earth today. Among the odontoceti, instead, there are for example dolphins and killer whales.
The branch of biology that deals with the study of these animals is cetology.
Having evolved from terrestrial ancestors, Cetaceans have had to develop remarkable anatomical and physiological adaptations in order to lead a completely aquatic life:
- the body is fusiform and has assumed a hydrodynamic shape similar to that of a fish;
- on the back a dorsal fin appeared, formed by connective tissue;
- the forelimbs have been transformed into pectoral fins (flipper) and have taken the form of paddles;
- the tail end is flat, formed by two lobes;
- the hind limbs are absent and of them remain small bones hidden inside the body;
- on the top of the head there is a breather;
- the hairs disappear completely after the first months of life;
- the auricles are absent;
- the external genitalia are hidden inside pockets.
At least 8 different species of cetaceans are present in the Mediterranean Sea, plus four considered occasional (this means they rarely enter the Mediterranean Sea through the Strait of Gibraltar).
In the pages below you can find information sheets on the species that can be seen during our excursions, accompanied by beautiful images.