Introduction When sorting the meiofauna from samples of coral sand of Bora Bay, Miyako Island, south of Okinawa (Japan), our colleague Dr. G. Boucher (Muséum National d'Histoire Naturelle, Paris) found many specimens of a very small undescribed Spadella. All stages of the life cycle of this new species were present. Material Thirty nine specimens were found and examined, in three out of five stations located on a transect from the coast to the reef across the lagoon of Bora Bay (coordinates: 24° 38’ N- 125° 35’ E) (Fig. 1), on October 20, 1995. Three replicate 10 cm 2 hand-cores were taken by SCUBA diving at each station and fixed immediately in 5% formalin. Sample collection was limited to the first five cm of the substrate. The meiofauna was extracted by Ludox TM centrifugation in the laboratory and sorted by hand. Cah. Biol. Mar. (2000) 41 : 137-141 A dwarf Spadella (Chaetognatha) from Bora Bay (Miyako Island, Japan) Jean-Paul CASANOVA and Yvan PEREZ Laboratoire de Biologie animale (Plancton) Université de Provence, Place Victor Hugo 13331 Marseille Cedex 3, France Reçu le 27 novembre 1999 ; accepté après révision le 15 mars 2000. Received 27 November 1999; accepted in revised form 15 march 2000. Abstract: A new benthic chaetognath, Spadella boucheri sp. nov., is described from Bora Bay, Miyako Island, near Okinawa (Japan). It is presently the smallest known species of the phylum. Its small size and the narrowness of its lateral fins suggest that it could live occasionally between the sand grains of the superficial substrate, a behaviour that had been previously hypothesized for a Spadella from the European waters. The problem of endemism of chaetognaths living in semi-closed bays of islands scattered in the open ocean is discussed. Résumé : Une Spadelle naine (Chaetognatha) de la baie de Bora (Île de Miyako, Japon). Un nouveau Chaetognathe ben- thique, Spadella boucheri sp. nov., est décrit de la baie de Bora, près d'Okinawa (Japon). C'est actuellement la plus petite espèce du phylum. Sa petite taille et l'étroitesse de ses nageoires latérales suggèrent qu'elle pourrait vivre occasionnellement entre les grains de sable à la surface du substrat, un comportement qui avait déjà été supposé chez une Spadella des eaux européennes. Le problème de l'endémisme des Chaetognathes vivant dans des baies semi-fermées d'îles disséminées en plein océan est discuté. Keywords : Chaetognatha, Spadella, Japan, taxonomy, endemism.