Nectozoa

	Nectozoa
Classification
;	Eudiktya
;	Episcleria
;	Phasakysta
Kingdom	Nectozoa
Distribution
	Miavegr
Number of species

Nectozoans are one of the three independently evolved animal-like kingdoms on Miavegr . Today Nectozoans can be found across all Miavegr. They form key parts of multiple ecosystems, from the open sea to shallow reefs.

Description

Nectozoans are mainly composed of haploid tissue with only some organs being haploïd. The haploïd organism is basally a tubular plasmodium with one opening, but more complex tissues (with divided cells) and complex organs evolved (mainly in Eunectozoa). They are ancestrally bilateral but their morphology varies heavily, with some clades having developed radial symmetry or an anus.

Reproduction

The adult haploid organism has diploid male gonads while the female gonads are part of the haploid tissue, these can produce gametes. Female gametes are formed by dikaryophysis of the female gonads; while male gametes are formed by tetraphysis of the diploïd tissue, these remain as a ciliated single cell. In Eunectozoans the female gamete already undergoes divisions inside the gonads. Then, somewhere in the development of the female plasmodium, it is fecundated by a male gamete. Some Nectozoans are fecundated early in their development and they can further their development only if they meet a male gamete, in extreme cases the female gamete is fecundated internally and is liberated by the gonads only after. Others can develop in a full organism before being fecundated. The diploid cell usually develops to form the gonads and usually other essential parts of the adult organism. While most of the haploïd tissues are replaced by cells derived from the tetraphysis of the diploïd tissue, after fecundation, the female gonads are always formed this way. Nevertheless some Nectozoans have completely lost their gonads and fully reproduce asexually by budding. Thus these usually contain nuclei with different genetics makeups, derived from the fact that they derive from the mother tissue and from different divisions of the diploïd tissue.

Evolution

Nectozoans evolved in the open seas of the Arizimian (beginning of the Neopoïkiloic) 550 Ma ago. Their history begins from earlier Episclerian colonies that thrived by the end of the Mesopoïkiloic. These formed benthic diploid stromatolithes and had a secondary free moving haploid plasmodium phase. Two of these plasmodia could fuse and form diploid cells. They then settled on the ground to give rise to a new sessile colony. In some of these organisms the haploid phase became more and more important, until the sessile diploid organism persisted only as a small part of the free floating haploid. It was around that time that Nectozoa and Manotnecta diverged. The nerarest common ancestor of Nectozoa, lived around 530Ma BP and was a simple plasmodium 1cm long with a single opening in the front, it fed by filtration thanks to its ciliated mouth. It could digest by liberating enzymes in its internal cavity. The first Eunectozoa appeared later, around the beginning of the Agherian (510 Ma BP), in conjuction with the rapid diversification of the Plicozoa and Diplozoa.