Arthracanthida, a sub-class of Acantharea

Acantharea

The Acantharea are a group of radiolarian protozoa, distinguished mainly by their skeletons.-Structure:These are composed of strontium sulfate crystals, which do not fossilize, and take the form of either ten diametric or twenty radial spines...

, is a group of marine protozoans. They consist mainly of a gelatinous sheath filled with cytoplasm

Cytoplasm

The cytoplasm is a small gel-like substance residing between the cell membrane holding all the cell's internal sub-structures , except for the nucleus. All the contents of the cells of prokaryote organisms are contained within the cytoplasm...

 and a skeleton of up to 20 radially placed spicule

Spicule

Spicules are tiny spike-like structures of diverse origin and function found in many organisms, such as the copulatory spicules of certain nematodes or the grains on the skin of some frogs.In sponges, spicules perform a structural function....

s made of celestite

Celestite

Celestine or celestite is a mineral consisting of strontium sulfate. The mineral is named for its occasional delicate blue color.-Occurrence:Celestine occurs as crystals, and also in compact massive and fibrous forms...

. While mostly found in the upper areas of the ocean, they are able to move vertically by using microfilament

Microfilament

Microfilaments are the thinnest filaments of the cytoskeleton, a structure found in the cytoplasm of all eukaryotic cells. These linear polymers of actin subunits are flexible and relatively strong, resisting buckling by multi-piconewton compressive forces and filament fracture by nanonewton...

s attached to the spicules to expand and contract the sheath. They are plentiful in the Gulf Stream

Gulf Stream

The Gulf Stream, together with its northern extension towards Europe, the North Atlantic Drift, is a powerful, warm, and swift Atlantic ocean current that originates at the tip of Florida, and follows the eastern coastlines of the United States and Newfoundland before crossing the Atlantic Ocean...

during the summer months, but little is known about their overall distribution.