The common trait that defines dartons from other decedents of the mason hexspourous is their quadrilateral symmetry. Two sets of hardened teeth-analogues line the mouth, which, along with the secondary oral appendages, help break down food for the dartons. Four breathing tubes are set around the body, which not only help to exchange gases but also with movement.
Breathing and Blood
The majority of the respiratory system is contained within the breathing tube. In decedents of the hexdarter, water is pumped in and out of the tubes through rippling contractions along those tubes that produce wave-like motions. The interior of the tube consists of a thin mesh of tissues, kept moist by bodily fluids, that perform gas exchanges. Some tissue functions to absorb oxygen, and some to release CO2 and other waste gases, with the oxygen absorbing one being clustered near the front, and the latter near the back. Running around the breathing tubes are a cluster of ring-shaped arteries, which transport the gases via the queft's blood. The "hearts" mentioned are just single-chambered pumps found at even intervals. Aquatic species have less tissues to allow greater mobility, but this is compensated for by the amount of water being moved through the tubes. Decedents of the hexdigger have their tubes closed off at the front to prevent damamage by sediment; instead near-microscopic holes pepper the exterior of the tubes, and allow gas to enter and leave. Like all decedents of the mason hexspourous, their blood is copper based, and therefore blue.
Diet & Energy
All dartons are heterotrophic, although methods vary greatly from lineage to lineage. Decedents of the hexdarter are generally carnivores, while hexdigger decedents can, depending on the line, range from detrivores to parisites.
Both branches use their breathing tubes to move; decedents of the hexdarter force water through their breathing tubes, while hexdigger decedents rotate slowly, allowing their twisted breathing tubes to propel them through dirt or flesh.
Dartons are asexual, and either inject eggs into a carcass, or simply let them gestate inside themselves, letting them eat their way out of the parent.
Dartons have two primary senses, smell and touch. Hexdarter decedents generally have a well developed touch sense, allowing them to form a mental map of their surroundings by detecting vibrations in the water.
The size of dartons varies widely, from just a few millimeters to the some of the largest marine species.