Ctenophores (Phylum Ctenophora) are carnivorous marine organisms with fragile gelatinous bodies. They are wide-spread in all waters from polar to tropical regions, but they are still very poorly known because of the difficulty in collecting them whole and preserving them intact. The phylum is divided into two classes, Nuda (or Atentaculata) and Tentaculata, depending on the presence or absence of tentacles. Nuda contains the single order Beroida whereas Tentaculata consists of six orders: Cydippida, Platyctenida, Ganeshida, Thalassocalycida, Lobata and Cestida (Harbison & Madin, 1982; Harbison, 1985), though recent research suggests that the Cydippida is polyphyletic (Podar et al., 2001).
Among the families of the order Lobata, Bathocyroidae is a monogeneric family represented by Bathocyroe that includes just two described species, Bathocyroe fosteri, originally collected from the mesopelagic zone below 200 m depth in the North Atlantic, and B. paragaster reported from the surface waters of the Cook Strait of New Zealand in the South Pacific Ocean. These two species of Bathocyroe, both possess the following features: (1) interradial canals issuing from an infundibular canal, (2) branches of paragastric canals extending to lowest edge of oral lobes, (3) subtentacular meridional canals connecting with branches of paragastric canals at lowest edge of oral lobes, (4) substomodaeal meridional canals uniting with subtentacular canals at lower margin of oral lobes, and (5) flapping movement of the oral lobes as seen in Ocyropsis. Several bathocyroids, presumably undescribed species, have been observed in situ by zoologists using research submersibles in the North Pacific, North Atlantic and Mediterranean (e.g., Youngbluth et al., 1988; Lindsay, 2005; Lindsay & Hunt, 2005; Burton & Lundsten, 2008; Mills et al., 1996; Kitamura et al., 2008; Lindsay & Miyake, 2009), but no detailed descriptions of these taxa have been made.
In this paper, we describe a new species in the genus Bathocyroe, based on two intact specimens collected from the epipelagic fauna of Japanese coastal waters.