Odanian

The Odanians were a sentient non-humanoid, Cetacean species. They were Federation members by late 24th century. ( episode: "SB-24")

Physiology and psychology
Physically, Odanians were large, averaging at least 6 meters in length, and were similar in appearance to Earth dolphins, though slimmer, with darker gray skin. They could not survive out of water.

Their brains had a remarkable ability to process spatial acuity, making them excellent at navigation, pattern recognition and scientific theory.

The Odanian language consisted of a series of clicks and whistles, again similar to dolphins, as well as higher frequencies and multiple wavelengths. Were a dolphin to hear an Odanian's calls, it would sound like two dolphins were "speaking" instead of one.

Odanians were known to be friendly and curious, and historically, were highly amused by the similarities between themselves and the dolphins of Earth. Likewise, they also found interacting with humanoids who visited their aquatic environment amusing. ( episode: "SB-24")

Within the Federation
Odanians were renowned as navigators and some of the most gifted physicists within the Federation.

Some Odanians served as Starfleet officers in the 24th century. In 2381, 22 Odanians led by Dr. Yata joined the crew of the USS Ross (NX-76710) at Starbase 24, comprising the ship's Cetacean Operations department.

Odanians serving aboard Starfleet vessels typically had L-shaped neural implants on either sides of their heads that allowed them to connect with the ship's computer cores and utilize the universal translator's vocorder capabilities, allowing them to speak with the humanoid crew. ( episode: "SB-24")