Polyphyllophyta

Polyphyllophyta (meaning 'many leaves plant') is the clade containing all multicellular organisms that form a symbiotic relationship with phototrophic microbes, granting them virtually unlimited food source and becoming strictly autotrophs.

Polyphyllophytes evolves from phyllostomes that live in shallow water, making them in constant contact with the microbes. They started as the microbes residing in phyllostomes' shells for protection. Eventually, the phyllostomes take the microbes into their bodies, which proved to be even more beneficial to both organisms. The microbes within the body proliferate quickly and widely spread through the whole body. The phyllostomes gain even more nutrients from the numerous microbes within the body, which in turn making them becoming larger.

Some species grow so large that they need air sacs to keep them straight up and their "root" can't hold them against water current anymore. Those that detached float around on the water surface and never replant themselves again.

Anatomy
Being a phyllostome lineage, polyphyllophytes have a body with radial symmetry. Unlike any of their cousins, however, some species of polyphyllophytes are gigantic, while some others are not much larger than a euphyllostome.

Photosynthesis
The relationship between the two organisms starts as the microbes take refuge in the shell of phyllostomes. Microbes that wander too close to the appendages are eaten normally. Over time, the microbes release excess sugar into the water, which is taken by the phyllostomes, nourishing them. Eventually, the hosts no longer seek other food sources than sugar, causing them to lost the ability to digest other substances. While consuming sugar, they sometimes accidentally swallowed the microbes. Instead of expelling them, the microbes are kept within their bodies, which is a perfect condition for the microbes to proliferate. Over time, the microbes merge with the cells of their host and enter cell division at the same time as the host cells. In the end, the two organisms became one, inseparable from one another.

"Leaves"
As they became an autotroph, the appendages are no longer needed to catch planktons. Instead of losing them, the appendages are repurposed to be a photosynthetic site. Over time, with the increased size, grow more of these "leaves" to increase the photosynthesis capability, potentially increasing their size to the upper limit. They can regenerate the leaves when lost at a very rapid rate, only taking five days for the new leaf to become fully functional.

Nervous System and Senses
Though not needed, polyphyllophytes still retain the nerve net present in the phyllostomes. This making them somewhat capable of "swim" to some degrees.

Loss of Shells
Due to the increased size, forming hard shells of calcium sulfate becomes problematic. Calcium sulfate is also not flexible. Instead, they form cellulose cell walls out of the excessive sugar on every epithelium cells. The cellulose cell walls offer a rigid yet flexible body structure. Later species of polyphyllophytes even reducing their mesohyl into only several connected tubes use to transport nutrients and gases. The cells also grow inward which strengthen the stem even further.

Behavior
Unlike their ancestors, phyllostomes no longer need complex behavior due to them becoming autotrophs, making them not needing to move their leaves around as much as their ancestors. However, they can move their leaves around to reposition themselves.

Reproduction
Polyphyllophytes retain the technique used by their ancestors. Due to the increased size, their gonopore is relocated to be near the "canopy" as well as developing to have several gonopores. Unlike their ancestors, they are capable of producing both the sperms and the eggs, however, only the sperms are released while the eggs are kept exposed on a stalk waiting for sperms. The eggs then detach when fertilized. The egg cells also contain chloroplasts to be utilized by the young.

Competitors and Predators
Polyphyllophytes only have to compete between themselves and photosynthetic microbes in the water for sunlight and carbon dioxide. Although they are sometimes eaten by pachypterids, they are not the popular target due to them having tough cell walls that are hard to tear and digest.

However, there emerges a creature that is capable of effectively eating the leaves of polyphyllophytes.

Diet
With the photosynthesis capability obtained from the microbes, polyphyllophytes no longer need to consume other microbes. Their choanocytes are no longer served for catching nutrients but instead used to exchange gases needed for photosynthesis. However, this prevents them from living in a place with no sunlight.

Distribution and Habitats
Polyphyllophytes can be found nearly everywhere, but the populations are higher in the tropical zones where there's high sunlight all year round. They thrive well up to a depth of around 200 meters. Those that live in shallow water have short stature while those that live deeper can reach the height of several meters.