Bulbozoa

Bulbozoa (meaning 'round animal') is the clade containing all heterotrophic origin, multicellular organisms found on the alien planet.

Bulbozoan evolves from heterotrophic microbes that clustered together into colonies. Eventually, becoming full-fledged multicellular organisms.

Although heterotrophic in origin, some clades derived from Bulbozoa became an autotroph, such as the Polyphyllophyta.

Anatomy
Being the earliest multicellular organism, they retain several traits of their ancestors. Bulbozoa have a rounded body with barely to no symmetry. Later bulbozoa' bodies either become slimmer or more rounded. Some of the slimmer ones evolve up to three pairs of fins, while the more rounded ones rolling around on the seafloor.

Nervous System and Senses
Bulbozoa have a simple, decentralized nerve net innervating the whole body. Covering their body are cilia used for both movement and sensing.

Mesohyl
Similar to sponges on earth, the inside of a bulbozoan is filled with a gelatinous matrix, which helps in retaining their shape. The mesohyl of bulbozoa is composed of collagen and amoebocytes. Amoebocytes transport nutrients, oxygen, and wastes to various parts of the body while collagen fibers provide platforms for cell adhesion.

Behavior
Bulbozoa possess no complex behavior and only able to perform basic tasks needed for surviving, such as catching food and breeding.

Reproduction
The early bulbozoa possess no reproductive system, and reproduce asexually through binary fission, which led them to quickly spread through the whole ocean.

Niche
Bulbozoa feed on planktons floating in the ocean current. Being the earliest multicellular lifeforms, they have no competitors other than themselves at that time period.

As time goes and life emerges, more creatures compete for the same food source, and they easily fall prey to larger creatures as well.

Distribution and Habitats
From the origin point, the population of bulbozoa explodes within a year, spreading through the whole ocean. During the period of 3 billion to 4 billion years, in which bulbozoa are the only multicellular organism on the planet. They can be found everywhere, from a coastline to the deepest trench. They only require a small amount of oxygen, which is a key to their success. Even in the present time, some can be found in an extreme environment within the ocean.