Basic biology of the 'vertebrates'[]

the anatomy snaiadi
All Snaiadi "vertebrates" have a two-headed system. The first head, extending from the "shoulders" and most easily recognized by humans as a head, typically has the eyes and ears (when present), and contains the reproductive organs. The eyes of Snaiad "vertebrates" are liquidless silicate lenses, surrounded by heat-sensing pads in most species, which enhance vision and allow the eyes to be small. The first head also usually has jaws, typically a beak or something analogous, which developed from bony sheaths that protected the reproductive organs of ancestral "vertebrates".
Although the first head often takes the role of biting and chewing, it does not actually consume the food, having no connection to the digestive tract. The true "mouth" is in the second head, which protrudes from the chest and varies from creature to creature, from a simple tongue-like organ of many Snaiad creatures, to the almost ungulate or kangaroo-like muzzle of the more advanced herbivores. A very few species can actually chew with their second head, such as the Tromobrachids, Jetocetes, and the advanced herbivores.
A Snaiadi "vertebrate's" digestive system is very similar to ours. First, the food goes from the mouth of the second head into the stomach, where it is digested. Afterwards, it passes into the intestines. There are two kinds of intestines in Snaiadi animals; thick and thin. Thick intestines seem to play a role analogous to the crop of a bird, and help to further break down the food. The thin intestines are similar to our intestines, both absorbing nutrients from the food and passing out waste products. Snaiadi animal waste products are rather dry and pasty, much like the waste products of the birds of our world.
Like Earth vertebrates, Snaiadi "vertebrates" have an internal skeleton. However, their "bones" are black or brown and made of a wood-like hydrocarbon, rather than calcium. These burn readily, and "vertebrate" fossils are not as common on Snaiad as on Earth. Another key difference between Snaidi "vertebrates" and Earth vertebrates is the presence of numerous hollows and indentations in the skeleton, which serve as anchorage points for the hydraulic muscles.
Most major muscles in Snaiadi vertebrates are hydraulic, working on the principle of pushing out with fluid rather than contracting and pulling the bone. These muscles are filled with fluid, which accumulates in fluid reservoirs in their pectoral armature and skid (the Snaiadi equivalent of shoulders and hips), to be cleaned. The hydraulic system also functions as the lymphatic system, and probably evolved from the water vascular system of their sea cucumber-like ancestors . Snaiadi "vertebrates" also have secondary muscles that are fibrous and work like those of Earth vertebrates.
The brain is located in the shoulders, typically very close to the digestive tract. Much like the muscular system, the nervous system of Snaiadi "vertebrates" displays an unusual duality, consisting of fluid-filled vessels along with more familiar fibrous "nerves"; the latter generate and receive electrical signals, while the former carry them along the body. This duality is also evident in the brain, which is actually two organs working in tandem, one being a dense knot of "nerves" and the other a bizarre, convoluted tangle of microscopic tubules in a sac called the worm basket, which contains millions of glands and vesicles communicating with each other via a cryptic alphabet of chemicals and protein equivalents. The worm basket seems to play a role in recording memories, and its tubules have been observed to twist, coil and corkscrew when an animal is dreaming or working on a complex task.
Snaiadi "vertebrates" were originally ovoviparous, and some (e.g. the Turtiformes and Polydactyls) still are. However, most living species are viviparous, keeping their young in a pouch inside their first head, slightly reminiscent of a marsupial. Snaiadi animals typically give birth by "vomiting" out the eggs or young. In some species with small first-head beaks, the young rip their way out of the pouch with specially developed womb-beaks. This is not harmful to the mother, as the pouch is not needed for anything else and rapidly heals over.