Sequence alignments of Corallicolids, apicomplexan symbionts of coral

Corals (Metazoa; Cnidaria; Anthozoa) have recently been shown to play host
to a widespread and diverse group of intracellular symbionts of the phylum
Apicomplexa. These symbionts, colloquially called ‘corallicolids’, are
mostly known through molecular analyses, and no formal taxonomy has been
proposed. Another apicomplexan, Gemmocystis cylindrus (described from the
coral Dendrogyra cylindrus), may be related to corallicolids, but lacks
molecular data. Here, we isolate and describe motile trophozoite (feeding)
corallicolids cells using microscopic (light, SEM, and TEM) and molecular
phylogenetic analysis to provide the basis for a formal description.
Phylogenetic analyses using nuclear and plastid rRNA operons, and three
mitochondrial protein sequences derived from single-cell transcriptomes,
all confirm that these organisms fall into a discrete deep-branching clade
within the Apicomplexa not closely related to any known species or major
subgroup. As a result, we assign this clade to a new order, Corallicolida
ord. nov., and family, Corallicolidae fam. nov. We describe a type
species, Corallicola aquarius gen. nov. sp. nov. from its Rhodactis sp.
host, and also describe a second species, Anthozoaphila gnarlus gen. nov.
sp. nov., from the coral host Madracis mirabilis. Finally, we propose
reassigning the incertae sedis taxon G. cylindrus from the order
Agamococcidiorida to the Corallicolida, based on similarities in
morphology and host localization to that of the corallicolids.