本科は3属からなり,本属は尾部後部が糸状に延長すること,側線が3列であることで他属と区別される。東部北太平洋に産するN. larseniでは,距離ABが距離ACより長い。太平洋,大西洋に産するN. curvirostrisでは,腹部に散在する少数の黒色素胞をのぞき,体はほぼ完全に白色で,体側には皮下の暗色縦帯が透けて見える(Nielsen and Smith, 1978)。 (上野・佐々木)
Distinctive characters:
Jaws long, produced like beak. Posterior end of body narrow and ends as a long filament. Five lateral line pores per segment resulting in 3 longitudinal rows of lateral lines (Fig.). Distance AB is equal to, or shorter than distance AC. No sensory ridges on head. The color is counter shaded, or uniform brown.
Distribution:
Cosmopolitan in tropical and temperate seas.
Remarks:
From the other 2 genera of the family, the present genus discernible by 3 lateral lines and caudal filament. In N. larseni, known from eastern North Pacific, distance AB is longer than distance AC. In N. curvirostris, known from the Atlantic and Pacific, body is completely pale with only few melanophores scattered along the ventral surface, and has subctaneous dark bars (Nielsen and Smith, 1978). (Uyeno and Sasaki)