There are many dolphins present in the ocean of Ecco's universe. Although some live solitary lives, most live in family units known as pods. Communication is done via clicks and sonar, also known as songs.
Most dolphins are friendly creatures that will aid Ecco throughout his adventures, either by giving him hints or rewarding him for meeting goals such as bringing a fish or winning a race. Some dolphins are aggressive, most notably the Clan.
Bottlenose Dolphins are the main cetacean species in the Ecco games. Ecco and his pod are Bottlenose dolphins. These species are fairly large. Breaching, chasing and playing is common for the species. Bottlenose dolphins occur in Ecco the Dolphin, Ecco Junior, Ecco: The Tides of Time and Ecco: Defender of the Future.
Short-beaked Common Dolphins are a secondary species of dolphin in Ecco: Defender of the Future that can be found throughout The Isle of Tranquility and making its first debut on Aquamarine Bay.
Atlantic Spotted Dolphin
Skyfins are an evolved species of dolphins featured in Ecco: The Tides of Time from the distant future with levitation abilities. They are larger than typical bottlenose dolphins, though resemble them in colouration. Some of them appear to have the ability to time travel at will. Trellia is the only notable (named) individual of her own kind throughout the entire game.
Orcas are a largest species of dolphin that appear in the classic series. They are not aggressive towards Ecco in any of the games and helps Ecco in search of his pod. Tara is a playable character in Ecco Junior.
Circle dolphins are a pale dolphin that resembles an Indo-Pacific Humpbacked Dolphin and similar to the Crimson and make its appearance in the Shrine of Controversy. In the Process that Never Ends, a Circle dolphin is shown to be capable of turning on the machinery back into working order once they knew what the prophecy needed to be done.
Crimson dolphins are noted by their red-tipped pectoral fins and resembles an Indo-Pacific Humpbacked Dolphin shape wise and similar to the Circle except they are smaller in comparison. They first appear in the Shrine of Controversy in Ecco: Defender of the Future.
Mover dolphins are brightly coloured and usually yellowish and colouration wise resemble Cuvier's Beaked Whale. They first appear in the Shrine of Controversy in Ecco: Defender of the Future and Movers tend to be the more aggressive compared to both the Circle and Crimson and caring for only themselves.
The Outcast are green dolphins which serves a prominent role (alongside with their arch-nemesis, the Clan) in the Dolphin's Nightmare scenario of Ecco: Defender of the Future. They have developed gills which removes the need to surface for air and making evasion somewhat easier. The Outcast's real enemies are the more notorious race, the Clan who are out to get them.
The Clan are an aggressive breed of dolphin first seen in Entrapment and serves a prominent role (alongside with the Outcast) in the Dolphin's Nightmare scenario in Ecco: Defender of the Future. These large half-orca species feature multiple spines and tusks. Most are yellow, green and black. Clan dolphins use crimson markings to identify their rank in the pod. The Clan often discriminate and harass the Outcast and other cetaceans in seek for power and superiority over others, seeing them as little to nothing in their eyes, even to the point where they use the Humpbacks in the Powers of Levitation to power up the generators to Hanging Waters.