Bicephalia

Bicephalians are one of the four major clades of the order Bilatera. As all other bilaterans, their symmetry is bilateral, but it is manifested (at least in some species) in a particular way: the body is separated in two (or three, in case of regular bilateralism) segments: the central part, which contains most of the major organs, and the side heads, which are equal between each other (save for their reproductive organs) and can, as well as eating, mating and expel waste, be repurposed for other uses, such as water expulsion in certain species. some bicephalians repurposed one of their mouths uniquely as the feeding one, while the other, losing this purpose instead, is dedicated to other uses. all bicephalians are hermaphroditic.

the bichepalian clade, with their wide range of forms and many even contrasting with the literal definition, is mostly based on ancestry than else. all the members of this clade cover low ranks in their ecosystems, and even the most succesful ones get quickly replaced by better animals in their niche, due to their fundamental limitations. still, the variety and even adaptability of the clade is not to be underestimated.

### **History**

The ancestors of the Bicephalians actually diverged a long time before every other bilateran, dating back to the first multicellular lifeforms of Nispe. these forms eventually managed to survive and evolve further into this weird bodyplan, giving rise to the true first bicephalians (like the amphisbenas). the form of those ancestors, nematode-like in appearance, is reflected into many of the existing bicephalians during their larval stage. during all of the benicene, all known bicephalian groups evolved, mainly the nematocephalians, the monocephalians and the thoracephalians. with the B-CH mass extinction, the nematocephalians went completely extinct: however, all other groups, in their currently existing forms, still survived and evolved during this time, with a few species of thoracephalians (the most succesful group to date) even venturing outside of water.

### **Groups**

#### **True Bicephalians**

This group is formed by all species that share the original bodyplan of the clade (centralized body with two mouths on the sides), and exclusively consists of bottom-dwelling species. the main representatives are the amphisbenes and the knuckers, more elaborate forms that gave rise to the other two existing main groups. both the mouths in these forms cover the tasks of eating, expelling waste and mating (with a different genital for each mouth), with no further specializations. despite their unfit bodyplan and characteristics for the current biosphere, until the Orchidian some amphisbenas still survived in the chodician as abyssal, anachronistic relics.

#### **Nematocephalians**

First bicephalians to undergo "cephalization" (by developing a mouth to specialize in hunting), the nematocephalians appeared early on during the first half of the benician. with less operation-intensive orifices and a sleeker body, the first nematocephalians were quick to take over their ancestors. but eventually the wirms, the basal species of the group, went extinct for unknown reasons, leaving behind only a diminuitive descendant: while clearly not as competitive as the others, the lengs are among the most derivative bicephalians, from the development of radial eyes, to the beak, down to even developing small protrusinons to move around in it's hideout. **Pitomorphs** are a deviation of the genre that took the adaptations and lifestyle of the lengs to the extreme, with a parasitical form evolved for pinning itself down into the skin of other animals, and even adopted this behavioural adaptation for reproductive purposes. all nematocephalians went extinct during the mass extinction that ended the benician, probably due to overpredation, or the lack of means to provide food due to their biology.

#### **Monocephalians**

The Monocephalian lineage started off with **Transitional forms**, which first evolved during the Benician. these forms, mainly represented by the meduses, are quite similiar to the ancestral bicephalians in shape, even retaining the double mouth structure. however, the main changes concerned the locomotion. no more bound to the sea floor, transitional monocephalians use water propulsion to swim around, provided by powerful muscles and air sacs in the mouth segments, as well as small fins to control their direction (which, in later forms, also took a more prevalent role as propulsion organs themselves). another change is the repurpose of the mouths to manipulators, aided by small tentacles on the sides, to snatch preys and grab/hold. True monocephalians first appeared in the later half of the Benician, with the rise of pillar forests. this group evolved even further by developing a cephalized central segment, even provided with crystalline eyes to scan the surroundings efficiently. another important characteristic is the development of standalone tentacles (more pronounced on later forms like the scilliyas), which took the place of the mouth itself as manipulators. oftentimes these tentacles are provided with claws, which are used as an offensive weapon. other adaptations of the true monocephalians include an external hard shell, which protects the central segment's insides, and fins fully adapted for swimming. During the Orchidian another branch of the monocephalians evolved, deriving from abyssal species developing a quirk in their appearance: **Lopsided Monocephalians**, or simply Lopsideds, are only provived with one manipulator, while the other is atrophied (in the original abyssal forms, it was converted exclusively into a bioluminescent organ). therefore, the main segment is also drastically rebuilt, especially with the mouth, which re-adapts as a propulsion organ, taking the role from the fins.

#### **Thoracephalians**

Thoracephalia is a wide, unified group of seafloor-dwelling, freshwater and even ground-dwelling species that, like nematocephalians, evolved a more traditional cephalization, but are also provided with an external shell, varying in complexity between genres. despite the grouping, in fact, thoracephalians are very diversified, which can make classification confusing at times. the first forms, evolved from similiar ancestors to monocephalians in the Benician, evolved a soft shell to protect their central segment from predators, but also a bite provided with a powerful toxin, another characteristic retained by many members of the clade. in the Chodician, Carcohs, soft-shelled thoracephalians, are among the first animals to reach the surface, but their dominion as main predators ended shorthly after the first keramouth's evolution. however, this genre became widely succesful in it's own ways. while hard-shelled thoracephalians existed well during the late benician, they didn't survive the mass extinction at the end of it. but eventually, these forms re-evolved during the latter parts of the Chodician, albeit way divergent from both these ancient forms and their ancestors themselves. freshwater forms have developed a mobile section of their lower shell, as wel as a saddle-shaped shell in itself, to allow vertical movement for the neck and head. Yuwes use this adaptation to blend among succugrasses, in order to ambush preys under them. other forms developed a big, spacious shell to retract their head in, but also to contain guts adapted to destroy the hard shells of their habitual preys during digestion. these forms, which tend to inhabit lower waters, also possess mobile flaps, developed from the soft central segment, to move and dig into the sand. as their evolution went on, this unique family diverged considerably enough to become a group of it's own, called **Palmicephalia**: among the clade as a whole, they are the most adapted at life outside of water, even spawning important forms in the early Orchidian that sadly went extinct with the ice ages.