KUBOKAWA, Kaoru*; YAMAMOTO, Tomoko; YAMANAKA, Toshiro; FUJIWARA, Yoshihiro; Ocean Res. Inst., Univ. of Tokyo, Tokyo; Kagoshima Univ., Kagoshima; Kyushu Univ., Fukuoka; JAMSTEC, Yokosuka: Habitat of novel species of amphioxus found in whale fall in Japan

Three species of amphioxus, Branchiostoma belcheri,　Epigonichthys lucayanum, Epigonichthys maldivensis, inhabit in Japan. In 2003, the forth species of amphioxus was found in the 230 m deep bottom of the sea and named later as Epigonichthys (Asymmetron) inferum by Nishikawa (Zool. Sci., 2005). This species has a peculiar urostyloid process which is a part of the notochord elongated backward from the tail. We propose to call E. inferum as the whale bone amphioxus, because the habitat of this amphioxus species is the bottom sand surrounded by whale bones. Sixteen sperm whales landed and died on a beach in Kagoshima Prefecture, southern Japan, in 2002. Twelve of the dead whales were thrown away to the sea and a survey with an echo sounder found six whale bodies in the bottom of the sea later in 2003. Research cruises were conducted to study a new ecosystem presumably generated by dead whale bodies in 2003, 2004, and 2005. We observed the whale bones by means of a remotely operated vehicle equipped with an under water video camera. The vehicle, Hyper Dolphin, belonged to Japan Agency for Marine-Earth Science and Technology (JAMSTEC). A number of the whale bone amphioxus was collected with a scoop from the bottom sand besides the whale bone. The body length of collected the whale bone amphioxus distributed between 10 mm and 30 mm with three peaks that might represent the presence of individuals from three generations in 2004 and 2005. The environment of the habitat of the whale bone amphioxus is considered to be anaerobic with abundant bacteria. This habitat is completely different from habitats of the other three species and the reason why this species had not been found for long time by 2003.