Genome assemblies and gene models of of the zoantharians Palythoa mizigama and Palythoa umbrosa

Anthozoan hexacorals are an important animal group in many marine
environments and include at least ~3,500 extant species. Zoantharia is an
order among the Hexacorallia (Anthozoa: Cnidaria) and is a sister group to
a clade consisting of four orders: Actiniaria, Antipatharia,
Corallimorpharia, and Scleractinia. Previously reported genomes from
scleractinian corals and actiniarian sea anemones have illuminated part of
the hexacorallian diversification. However, little is known about
zoantharian genomes and the early evolution of hexacorals. We generated
two Palythoa genomes from the order Zoantharia within Hexacorallia,
providing novel insights into early hexacorallian evolution by comparing
with genomes of diversified scleractinian corals and actiniarian sea
anemones. Draft genomes generated from ultra-low input PacBio sequencing
totaled 373 Mbp and 319 Mbp for Palythoa mizigama (Pmiz) and
Palythoa umbrosa (Pumb), respectively. 30,394 and 24,800 protein-coding
genes were predicted in genomes of Pmiz and Pumb, respectively.
Comparative genomic analyses identified 3,035 conserved gene families,
which were found in all analyzed hexacoral genomes. Some of the genes
related to toxins, chitin degradation, and prostaglandin biosynthesis were
expanded in these two Palythoa genomes and many of which aligned tandemly.
Extensive gene family loss was not detected in the Palythoa lineage and
five of ten putatively lost gene families (GRIN1, TAAR7E, FEZF2, NRXN3,
and SPATA7) likely had neuronal function, suggesting biased gene loss in
Palythoa. These first available gene-sets (gene models) from zoantharians
demonstrate genome conservation with restricted neuronal gene loss.
Overall, our analyses imply that lineage-specific tandem duplication of
enzyme genes have occurred in the genome evolution of Zoantharia.