According to Marjan Swantek, author of The Manx Cat, published in 1987 by TFH Publications, the longhaired gene was probably introduced to the population by a Norwegian Forest Cat, brought to the island by King Mangus of Norway.

The name Cymric (pronounced kim' rick) means Welsh; it was proposed since many longhaired Manx were observed in Wales, at one time. Initially, this name was used within all associations, but eventually, in some associations, the breed is called simply, Long Hair Manx. In ACFA, breeders have continued with the traditional name.

Their tail length classifies both Manx and Cymric cats. The ideal cat is a dimple rumpy, in which there is a complete absence of a tail. When gently touched, the total lack of a tail can be felt. The rumpy riser has a small piece of bone or cartilage at the end of its spine; in a relaxed state, this is not obvious. However, when excited, the rumpy riser can lift this little cartilage in an up and down motion. Both the rumpy and rumpy riser are eligible to be shown in championship classes. Other kittens may have a stump of a tail; these are called stumpies or stubbies. Still other kittens may have a full-length tail; some breeders will dock their tails so that they appear to be stumpies. Both the stumpies and tailed cats can not be shown in the championship classes. It should be noted that all kittens are registered as either Manx or Cymric, regardless of their tail length. In any given litter, there might be any combination of the tail lengths. It should also be noted that the tailless gene could be expressed too severely with the kitten having spina bifida. These unfortunate kittens can not walk properly and have bowel / bladder control problems. Most reputable breeders will have these kittens euthanized as soon as the problem becomes apparent. The tailless gene is a dominant gene which is lethal in the homozygous state (i.e. the kittens do not develop in the uterus) so all tailless cats are heterozygous. Because of the dominant nature of the gene, if a Manx or Cymric were to mate with any other cat, it is possible for tailless kittens to result; however, these are not considered to be pure-breed.

The double coat of a Cymric is a silky, medium length. When kittens are born, the coat is not that much different from a Manx. But, within a couple of weeks, the dense, plushy coat becomes obvious. A longhaired kitten may result from the breeding of two shorthaired if both carry the longhair recessive gene. If one parent is longhair, the kittens might be longhair or shorthair. If both parents are longhair, the entire litter will be longhair.

So, if one had two breeding cats (a Cymric and a Manx), it might take several litters to produce one show quality Cymric kitten. In addition to the tail status and hair length, other qualities that must be present in a show quality kitten include: a short, stocky body, a rounded head that is slightly longer than it is wide, a well-developed squarish muzzle with prominent whisker pads, large round eyes set at a slight angle downward toward the nose, tufted ears that when viewed from behind resemble the rocker of a cradle, a deep broad chest, sturdy front legs that are shorter than the hind legs, and a back that arches up in a gradual curve from the shoulder blades to the haunches with a round rump.

As household pets, these cats are superb. They tend to gravitate toward one person in the household. They become, literally, your best buddies. It is not unusual to find a Manx or Cymric in the lap of its owner or resting next to the owner. They are playful and energetic. Often, they will emit little trills of joy to be with you.