Heliorapha

Heliorapha is a genus of heliozoan protists, amoeboid eukaryotes with stiff axopodia radiating from their cells.^[2][3] It contains one species, Heliorapha azurina (previously Ciliophrys azurina). It is classified within a monotypic family Helioraphidae inside the actinophryids, a group of heliozoa that belong to the Ochrophyta along with other protists such as diatoms and brown algae.^[1]

Heliorapha
Scientific classification
Domain:	Eukaryota
Clade:	Sar
Clade:	Stramenopiles
Phylum:	Ochrophyta
Class:	Raphidomonadea
Order:	Actinophryida
Suborder:	Actinophryina
Family:	Helioraphidae Cavalier-Smith, 2013[1]
Genus:	Heliorapha Cavalier-Smith, 2013[1]
Species:	H. azurina
Binomial name
Heliorapha azurina (Patterson, 2001) Cavalier-Smith, 2013[1]
Synonyms[2]
Ciliophrys azurina Patterson, 2001

Morphology

Heliorapha azurina is a heliozoan, a unicellular protist with tapering arms called axopodia sustained by axonemes. Cells of H. azurina have a large, prominent cell nucleus containing a central nucleolus surrounded by peripheral clumps of heterochromatin. The cell body measures 15 μm in diameter, with radiating arms that contain extrusomes. Each cell has a single flagellum that appears at the front of swimming cells or, in non-swimming cells (i.e. during feeding), appears tightly curled, typically in a double "8" shape. Both its large size and the length and shape of its flagellum make it similar to Actinophrys, specifically A. pontica.^[2]

Ecology

Heliorapha azurina is a heterotrophic flagellate exclusively found in tropical climates, in both marine and terrestrial habitats.^[4] It was isolated from Darwin, Northern Territory, Australia, where it was observed consuming diatoms.^[2] It is present in intertidal sediments and surface waters of Darwin.^[5] It has also been observed in Ascension Island.^[6]

Systematics

Heliorapha azurina is a species previously assigned to the genus Ciliophrys of the Pedinellales, a heliozoan order assigned to Dictyochophyceae, a class of ochrophytes. It was created in 2001 by biologist David J. Patterson to describe cells collected in 1994 from East Point and Lee Point, Darwin, Northern Territory, Australia. In its initial publication, H. azurina (then Ciliophrys azurina) was considered an "evolutionary link" between the Pedinellales and the order Actinophryida, on the basis of presenting traits previously thought as exclusive to each order.^[2]

The species differs from Ciliophrys by the presence of tapering axopodia that are too broad at the base to be sustained solely by a triad of microtubules, a characteristic of Pedinellales. This incorrect assignment to the Pedinellales was approached in 2013, when protozoologist Thomas Cavalier-Smith moved the species to its own genus Heliorapha and family Helioraphidae. The family is currently assigned to the Actinophryida, in a suborder known as Actinophryina which unites both Helioraphidae and Actinophryidae.^[1]