Symphyacanthida

Astrolithium (astro-lith-ee-um) is one of the more commonly encountered acantharea. These star-shaped organisms used to be grouped with polycystines and phaeodarea as radiolaria. These three groups all have inorganic skeletons to which the cytoplasm attaches, usually have an inner condensed area of cytoplasm and an outer more open region, and have a star-like morphology. Like other acantharea, the spines of Astrolithium are made of strontium salts which readily dissolve when the cells die. There are 20 radiating spines which are linked together at the centre of the cell. The outermost region of cytoplasm attaches to the arms with contractile ligaments or myonemes about halfway along their length. The cells often have an orange or brown colour because of the presence of symbiotic dinoflagellates. Phase contrast.

Astrolithium (astro-lith-ee-um) is one of the more commonly encountered acantharea. These star-shaped organisms used to be grouped with polycystines and phaeodarea as radiolaria. These three groups all have inorganic skeletons to which the cytoplasm attaches, usually have an inner condensed area of cytoplasm and an outer more open region, and have a star-like morphology. Like other acantharea, the spines of Astrolithium are made of strontium salts which readily dissolve when the cells die. There are 20 radiating spines which are linked together at the centre of the cell. This image has been taken with polarised light so the the crystalline appearance of the arms is more evident. Phase contrast with polarised light.

Astrolithium (astro-lith-ee-um) is one of the more commonly encountered acantharea. These star-shaped organisms used to be grouped with polycystines and phaeodarea as radiolaria. These three groups all have inorganic skeletons to which the cytoplasm attaches, usually have an inner condensed area of cytoplasm and an outer more open region, and have a star-like morphology. Like other acantharea, the spines of Astrolithium are made of strontium salts which readily dissolve when the cells die. There are 20 radiating spines which are linked together at the centre of the cell. As can be seen in this micrograph, the outermost region of cytoplasm attaches to the arms with contractile ligaments or myonemes about halfway along their length. Phase contrast.

Astrolithium (astro-lith-ee-um) is one of the more commonly encountered acantharea. These star-shaped organisms used to be grouped with polycystines and phaeodarea as radiolaria. These three groups all have inorganic skeletons to which the cytoplasm attaches, usually have an inner condensed area of cytoplasm and an outer more open region, and have a star-like morphology. Like other acantharea, the spines of Astrolithium are made of strontium salts which readily dissolve when the cells die. There are 20 radiating spines which are linked together at the centre of the cell. The outermost region of cytoplasm attaches to the arms with contractile ligaments or myonemes about halfway along their length. Phase contrast.

Astrolithium (astro-lith-ee-um) is one of the more commonly encountered acantharea. These star-shaped organisms used to be grouped with polycystines and phaeodarea as radiolaria. These three groups all have inorganic skeletons to which the cytoplasm attaches, usually have an inner condensed area of cytoplasm and an outer more open region, and have a star-like morphology. Like other acantharea, the spines of Astrolithium are made of strontium salts which readily dissolve when the cells die. There are 20 radiating spines which are linked together at the centre of the cell. The symbiotic dinoflagellates which give the acantharea an orange or brown colour can be seen here. Differential interference contrast.

Astrolithium (astro-lith-ee-um) is one of the more commonly encountered acantharea. These star-shaped organisms used to be grouped with polycystines and phaeodarea as radiolaria. These three groups all have inorganic skeletons to which the cytoplasm attaches, usually have an inner condensed area of cytoplasm and an outer more open region, and have a star-like morphology. Like other acantharea, the spines of Astrolithium are made of strontium salts which readily dissolve when the cells die. There are 20 radiating spines which are linked together at the centre of the cell. This image shows a young cell attached to a larger cell. Phase contrast.

Haeckel says: The central capsule contains numerous spherical nuclei and is enclosed by the hyaline calymma, which forms conical sheaths around the spines.