ascidian Cnemidocarpa verrucosa

Cnemidocarpa verrucosa is found throughout Antarctica and the Antarctic Peninsula, South Shetland Islands, South Orkney Islands, South Sandwich Islands, South Georgia Island, Kerguelen Island, Bouvet Island, Crozet Island, Falkland Islands, and Tierra del Fuego from 5 to 761+ meters depth [2,7,8,10]. The body shape of C. verrucosa may be cylindrical, ovate, or barrel shaped [2]. C. verrucosa has a thin, tough, flexible, opaque body covering (test) whose surface may be smooth or roughened by furrows, wrinkles, and conical or low wart-like papillae [2]. The test of ascidians is an acellular covering secreted by the epidermis; it is largely made of tunicin, a substance allied to plant cellulose and the only cellulose-like substance to occur in the animal kingdom [6]. The body wall of C. verrucosa is thin and adheres closely to the test [2]. C. verrucosa may have a short stalk with larger specimens having a expanded jelly-like plate at the stalk's base [2].



Cnemidocarpa verrucosa lives at least four years and can be quite large; maximum size has been described as up to twenty centimeters in diameter or as eighteen centimeters long and nine centimeters in diameter [1,2,9,10]. The larger incurrent branchial siphon of C. verrucosa is curved over with its flared opening facing downward; the smaller excurrent atrial siphon faces upward from the body [2].

C. verrucosa color varies among specimens and with age: white, white with a rosy and yellow tinge, bright yellow (a predator Marseniopsis mollis is bright yellow), yellowish-brown, orange, brown, or gray and it can be bright yellow around its apertures [2,10].

C. verrucosa feeds on diatoms, nanoplankton, bacteria, and detritus [13].



Here Cnemidocarpa verrucosa is perched on top of the slimy sponge Mycale (Oxymycale) acerata.

C. verrucosa is the largest and most abundant Styelidae ascidian in the Antarctic Ocean [9]. C. verrucosa is oftentimes attached to cobblestones or boulders and may be clustered with several others of its species; one study site had a C. verrucosa population density of 0.4 individuals per square meter at 20 - 30 meters depth [1].

C. verrucosa has released gametes for external fertilization in the laboratory in November and their planktonic larvae appear to be yolk-feeders [1].

Younger Cnemidocarpa verrucosa are almost cylindrical, attached by their posterior, and are covered with characteristic pointed test protuberances [2,5,9].

The bright yellow prosobranch mollusc Marseniopsis mollis is the primary predator of C. verrucosa; no seastars or fish have been observed eating C. verrucosa [3,4]. Marseniopsis mollis is shell-less and appears to be protected from predation itself by a chemical, homarine, which deters feeding [3]. M. mollis appears to obtain its defensive chemical homarine from bryozoans and hydroids growing on the surface of C. verrucosa [3]. M. mollis has been observed drilling into the tunic of C. verrucosa to deposit its eggs [4]. The gastropod Phyline antarctica also deposits its eggs in the tunic of C. verrucosa [12].

1: Journal of Experimental Marine Biology and Ecology 147(2):163-175, 1991; 2: Antarctic Ascidiacea; Monographic Account of the Known Species Based on Specimens Collected under U.S. Government Auspices, 1947-1965. Kott, Patricia. Washington, DC : American Geophysical Union, 1969. Antarctic Research Series. Volume 13; 3: Antarctic Journal of the United States 29(5):151-153, 1994; 4: Ecological Monographs 44(1):105-128, 1974; 5: Further Zoological Results of the Swedish Antarctic Expedition 1901-1903. Volume 4, Number 4. Ascidiacea Part 2. A Arnback-Christie-Linde. Stockholm : PA Norstedt and Soner, 1950; 6: Patricia (Kott) Mather, personal communication, 1999; 7: Biology of the Antarctic Seas 4:11-82, 1971. Antarctic Research Series 17; 8: Memoires du Museum National d'Histoire Naturelle. Nouvelle Serie. Serie A, Zoologie 125:1-168, plates, 1983; 9: Bulletin du Museum National d'Histoire Naturelle. 4e Serie. Section A, Zoologie, Biologie et Ecologie Animales 16(1):13-37, 1994; 10: Tethys 5(4):611-628, 1974; 11: Polar Biology 20(4):229-247, 1998; 12: Berichte zur Polarforschung, Reports on Polar Research 286, 1998; 13: Polar Biology 25:58-64,2002

Text ©Peter Brueggeman. Photographs ©Norbert Wu. Photographs may not be used in any form without the express written permission of Norbert Wu. Norbert Wu no longer grants permission for uncompensated use of his photos under any circumstances whatsoever; want more info?