Dorataspid acantharean, the cytoplasm is attached to the radiating strontium sulphate spicules by contractile myonemes. The outer cytoplasm (ectoplasmic layer) is filled with vacuoles, and most of the cytoplasmic organelles are located within the central capsule which is orange. The acantharea are one of the four types of large amoebae which occur in the marine water column. Dark ground image by Linda Amaral Zettler. This is one of a collection of images assembled by Dave Caron (University of Southern California, Los Angeles). Image copyright: image used under license to MBL (micro*scope).
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From the collection
Marine planktonic amoebae and other protists
|Description of Acantharea: Circumscription: One of several groups previously referred to as radiolaria;-large marine unicells with radiating axopodia and an inorganic skeleton (in the case of Acantharea composed of 10/20 spicules made of strontium sulphate). Cell with central endoplasm and peripheral ectoplasm separated by a fibrous capsular wall, outside face of cytoplasm coated with a fibrous cortex that is joined to spicules by contractile myonemes. Often with symbionts. No propulsive organelles in trophic form but may have flagellated stage and/ or amoebas and/or cysts in life cycle. Ultrastructural identity: Not well established because of difficulty of good preservation. Mitochondria with tubular cristae. Axopodia arising from unspecified sites in the cytoplasm but having an open hexagonal or larger polygonal arrays of microtubules; periplasmic cortex, axopodial details, extrusomes, and so forth. With concentric extrusomes. Mitosis involves an eccentric spindle located inside an intact nuclear envelope. Synapomorphy: Tubulocristate protists with strontium sulphate skeleton with symmetry based on 20 radial elements. |