I have already given to you a physical description of a hippocampus (very first page)  but incase you missed it.......  A hippocampus is a mythological creature consisting of a cross between a equine and a dolphin or fish of sorts.  A hippocampus features fins in replace of a hair-like mane, hooves, and it has one large tail in the back. Greatly resembling a mermaid tail.  Anyhow, A hippocampus tends to be bulkier, more stalky than a campchurch.  In most cases it is more muscular and is indeed a better swimmer thanks to it's tail.  Allow me to elaborate....

 

A campchurch is much like a hippocampus in that it is also a cross between a equine and a fish, but a campchurch has four limbs where a hippocampus only has two true limbs.  A campchurch is often depicted without a tail, making it the less efficient swimmer.  A campchurch is also often draw with a real mane, apposed to the fin-mane of the hippocampus.  Campchurches are also depicted with a horn. Campchurches are also known as 'Sea Unicorns', for they have a horn and possess magical qualities that the hippocampus lacks.  I'm not saying this applies to every single hippocampus and every single campchurch, I'm talking about the general majority. There is such a thing as a hippocampus mage, or a fluke non-magical sea unicorn. 

 

Hopefully this has cleared up a few things for those of you who were confused *grins*  ^_~