crinoid Promachocrinus kerguelensis

Promachocrinus kerguelensis is found throughout Antarctica and the Antarctic Peninsula, South Shetland Islands, South Georgia Island, Bouvet Island, Kerguelen Island and Heard Island, from 10 to 2,100 meters depth [3,4,6]. P. kerguelensis is also found between Australia/New Zealand and the Antarctic continent [3,4]. P. kerguelensis has ten biradiate rays (20 arms), is the most widely distributed and abundant crinoid in Antarctica and subantarctic islands, is the largest comatulid (unstalked) crinoid in southern latitudes, and is the only 20-armed comulatid crinoid in high southern latitudes [3,4]. Here Promachocrinus kerguelensis is seen perched on a large volcano sponge Anoxycalyx (Scolymastra) joubini.

Promachocrinus kerguelensis can be solid colored or banded; its color ranges from ivory to buff with light to dark brown pinnules and if banded, the bands can be dark to reddish brown [3,4]. Individuals from the Ross Sea may be more uniform in color; solid color and banded specimens can occur in the same population [4].



The arms of Promachocrinus kerguelensis are edged with feathery pinnules containing sensory tube feet and reproductive organs. The arms are used to trap drifting plankton and they have grooves down which food particles are carried by hair-like cilia to the upward-facing mouth. Its different feeding postures (a filtration fan, a radial posture with its pinnules in one plane, and a collecting bowl) are suggested as a response to ocean currents [3].

Promachocrinus kerguelensis (and other comatulid crinoids) cling and move by walking on specialized curved structures called cirri (seen at lower right). P. kerguelensis clings to sponges, worm tubes, gorgonians, and rocks as well as mud and gravel [2,3]. This gives P. kerguelensis a high perch above the seafloor which may protect it from fish nibbling on its extended arms [2]. P. kerguelensis is not toxic to fish but there are no Antarctic fish living in the water above the seafloor to nibble at its arms [2]. The predatory brittle star Ophiosparte gigas has been found to have P. kerguelensis in its gut contents [5].

Promachocrinus kerguelensis produces large numbers of buoyant eggs which it spawns into the plankton in November and December in McMurdo Sound; it doesn't brood eggs in its arms as do some Antarctic crinoids [1]. Settlement of its free-floating larvae occurs 2 to 3 months later when the seasonal antarctic plankton bloom is high and offers a rich food source [1].

1: Marine Biology 96(3):375-383, 1987; 2: Polar Biology 9(7):461-465, 1989; 3: Biology of the Antarctic seas XIII. Louis S. Kornicker, ed. Antarctic Research Series Volume 38. Washington, DC : American Geophysical Union, 1983. pp.1-60; 4: Comatulid Crinoids from R/V Eltanin Cruises in the Southern Oceans. Janis A. Speel. University Of Maine PhD dissertation. 1976; 5: Polar Biology 16(5):309-320, 1996; 6: Tethys 6(3):631-653, 1974

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