(whose outward representation, for now, are the three dolphins Plums in a Box, Guess Who? and Trilldick) are not precisely
dolphins, but are
large-brained marine animals with sonar.
They are written by Mutt, who is willing to share their (originating) setting and species.
Trilldick is the Twine Wars viewpoint character out of the three above named.
All this be subject to change yo.
Their heads are similar to a bottlenose dolphin's 
, although they may have extended, flexible upper lips. (do we think tapir style?  
?) They have blowholes and 'melons', dark eyes set to the side and snouts with teeth.
They have pelvic 'fins' - repurposed ex-hind-legs more recently (evolutionarily speaking) used for grip/stability during mating - that function well enough to hold objects.
They are highly social animals with pod behaviour similar to dolphins'.
They are 'hermaphrodites'. Once they have mated the first time with their 'male' genitalia, they are thereafter 'female'.
[Size comparison with generic human]
They are from a world whose seas are packed with large carnivorous cetaceans that look like something out of a hippie's nightmare (think similar to [Orcas a la Steven Brust]
). As soon as they find a worldgate
, they are outta there