Phylum Radiozoa. Radiolaria

HOLLIS CHRIS; LUER V; AITA Y; BOLTOVSKOY DEMETRIO; HORI RS; OCONNOR BM; TAKEMURA A

New Zealand Inventory of Biodiversity, Volume Three: Kingdoms Bacteria, Protozoa, Chomista, Plantae, Fungi

Canterbury University Press

Lugar: CHRISTCHURCH; Año: 2012; p. 288 - 305

Radiozoa (‘ray animals’), commonly referred to as radiolaria, are exquisite planktonic organisms with ornate skeletons of opaline silica or the mineral celestite (strontium sulphate). Most have radial symmetry – with spectacular variations of form based on spherical, ellipsoidal, discoidal, and conical skeletal frameworks. Individuals vary in size from hundredths of millimetres to several millimetres. Colonial forms can be very much larger, with tests organised simply as an association of loose rods or there may be no hard parts at all. The cell is organised into a porous central capsule that contains the nucleus, mitochondria, and other important organelles that carry out core cell functions like respiration and reproduction. Radiating from this capsule are ray-like spokes. Pseudopodia (actinopodia or axopodia) surround these spokes, capturing prey, disposing of wastes, and reacting to external stimuli, aided by irregular rhizopodia. Outside the central capsule, surrounding the spokes, the cytoplasm is frothy, with bubble-like alveoli, presumably a flotation device, disappearing when agitated and reforming when the individual has sunk to some depth. This part of the cytoplasm includes fewer mitochondria, digestive vacuoles, and, depending on the species, algal symbionts.