Birkeland, Charles (בפברואר 1974). "Interactions between a Sea Pen and seven of its predators". Ecological Monographs. 44 (2): 211–232. doi:10.2307/1942312. JSTOR1942312. {{cite journal}}: (עזרה)
jstor.org
Birkeland, Charles (בפברואר 1974). "Interactions between a Sea Pen and seven of its predators". Ecological Monographs. 44 (2): 211–232. doi:10.2307/1942312. JSTOR1942312. {{cite journal}}: (עזרה)