Swimming behavior of the spoon worm Urechis unicinctus (Annelida, Echiura).
Large numbers of swimming and stranding Urechis unicinctus were observed at night during low tide in Sasuhama, Miyagi Prefecture, northeastern Japan, during the periods from January to February in 2012 and 2013. Worms did not drift passively but swam actively, therefore hinting at a certain purpose for such behavior. As trochophore larvae of U. unicinctus were observed to occur simultaneously in the plankton, we infer the possibility that this is an event of reproductive swarming. Anatomical observations of both swimming and stranding U. unicinctus showed that none of the specimens had gametes, which may suggest that these were completely spent after spawning. Urechis unicinctus seemed to begin swimming after dusk and the observed swimming behavior occurred during the evening ebb tide throughout the night low tide during winter time. Stranding U. unicinctus have long been known in Japan and have been attributed to sea storms. The present study shows for the first time the possibility that U. unicinctus swims in order to reproduce at night and that this swimming behavior is closely linked to the stranding of U. unicinctus individuals.
Laboratory of Biological Oceanography, Graduate School of Agricultural Science, Tohoku University, 981-8555, Japan. Electronic address: abehiro13@gmail.com.
Hirokazu
H
Abe
Laboratory of Biological Oceanography, Graduate School of Agricultural Science, Tohoku University, 981-8555, Japan.
Waka
W
Sato-Okoshi
Laboratory of Taxonomy, Department of Biology, Faculty of Science, Toho University, 2-2-1, Miyama, Funabashi, Chiba 274-8510, Japan.
Masaatsu
M
Tanaka
Laboratory of Marine Biology, Department of Environmental Science, Faculty of Science, Toho University, 2-2-1, Miyama, Funabashi, Chiba 274-8510, Japan.
Kenji
K
Okoshi
Laboratory of Biological Oceanography, Graduate School of Agricultural Science, Tohoku University, 981-8555, Japan.
Wataru
W
Teramoto
Laboratory of Biological Oceanography, Graduate School of Agricultural Science, Tohoku University, 981-8555, Japan.
Tomohiko
T
Kondoh
Laboratory of Biological Oceanography, Graduate School of Agricultural Science, Tohoku University, 981-8555, Japan.
Goh
G
Nishitani
Laboratory of Biological Oceanography, Graduate School of Agricultural Science, Tohoku University, 981-8555, Japan.
Yoshinari
Y
Endo
D000818:Animals; D000845:Annelida / Q000235:genetics / Q000502:physiology*; D007564:Japan; D008969:Molecular Sequence Data; D012337:RNA, Ribosomal, 18S / Q000235:genetics; D012726:Sexual Behavior, Animal / Q000502:physiology*; D013550:Swimming
D012337:RNA, Ribosomal, 18S
Echiura; Reproductive swarming; Stranding; Swimming behavior; Urechis unicinctus