brittle star Astrotoma agassizii

Astrotoma agassizii occurs throughout Antarctica and the Antarctic Peninsula, South Shetland Islands, South Georgia Island, Falkland Islands, Shag Rocks, Burdwood Bank, and southern Chile and Argentina in depths from 55 to 1,335 meters [1,2,3,4,8]. The unbranched arms of A. agassizii are stout, tapering, and flexible, reaching a length of seventy centimeters [2,6]. A. agassizii is creamy white in color [2].

The central disk of A. agassizii can reach a diameter of six centimeters [2,6]. From its growth rings, maximum age of A. agassizii is estimated to be 91 years [7]. A. agassizii bears live young, and is hermaphrodite [3].

Here's Astrotoma agassizii at Granite Harbor. A. agassizii is usually found on sponges (as shown here on Anoxycalyx (Scolymastra) joubini), corals, and other organisms on which it can climb to be more advantageously placed to feed on prey drifting by [1,2]. The stomach of A. agassizii contains diatoms, phytoplankton, foraminiferans, chaetognaths, bryozoans, polychaetes, holothurians, ascidians, and primarily crustaceans (including mysids, copepods particularly Euchaeta antarctica and Calanoides acutus, euphausiids, and amphipods, ostracods), indicating that it feeds on plankton, catching them with its flexible long arms, which are armed with hooks and spines to increase catch efficiency [1,2,5,6,7]. One or two arms cling to the perch, while the others extend to feed [6]. The arms of A. agassizii can be looped and twisted, increasing its efficiency at contacting prey [1]. Prey caught by the arm tips of A. agassizii are rolled up into coils, and passed to the mouth [1].

1: Adaptations within Antarctic Ecosystems, Proceedings of the Third SCAR Symposium on Antarctic Biology. GA Llano, ed. Washington, DC : Smithsonian Institution, 1977. pp.293-326; 2: The Fauna of the Ross Sea, Part 1, Ophiuroidea. HB Fell. New Zealand Department of Scientific and Industrial Research Bulletin 142, New Zealand Oceanographic Institute Memoir 18, 1961; 3: Physis 25(69):2-5, 1965; 4: US National Museum Polar Invertebrate Catalog at http://www.nmnh.si.edu/iz/usap/usapdb.html; 5: Journal of Plankton Research 11(6):1315-1320, 1989; 6: Antarctic Research Series 44:1-28, 1986. Biology of the Antarctic Seas, Volume 17. Washington: American Geophysical Union, 1986; 7: Berichte zur Polarforschung 194, 1996; 8: Boletim do Instituto Oceanografico (Sao Paulo) 32(1):33-54, 1983

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