An otter is more than the sum of its parts because its individual parts are not alive while the otter is, it is the assembly to a whole being that makes it alive.
The individual parts of the otter must by necessity resemble the characteristics of the otter as a whole, and the characteristics of the otter must be reflected in its individual parts, because it is this integrity that makes the otter what it is.
Every part of the otter must follow and adhere to the essential otter-ness so that the total sum of the parts is an otter. This essential characteristic is "otteriness". If a part of an otter is not ottery then it is foreign, as with things such as parasites and worms which can be found in wild otters, these may be part of the otter's body but they are not ottery hence foreign and destructive.
Imagine this: An otter with the tail of a fox. Is the otter still an otter? The tail of an otter makes up part of the otter's essence while at the same time the otter's otteriness (i.e. its state of being, its character) is reflected in the otter's tail.
If an otter had a tail of a fox, not only would its ability to swim be diminished (one of the key characteristics of an otter), but aesthetically it would no longer truly resemble an otter.
In a similar way the tail of a fox is a part of the fox and makes the creature that bears it more akin to a fox in essence. Hence imagining such a creature, an otter with a fox's tail, it must be neither a fox nor an otter because each of these are only complete with their specific body parts possessing integral characteristics.