抄録
Ten pelagic juveniles (21.2-16.2 mm in standard length, SL) of the morid Laemonema longipes Schmidt, 1938, collected from off northeastern Japan, are described, with special reference to their ontogenetic changes. The present juveniles all have the following characters: an elongated body, long dorsal and anal fin bases, elongated pelvic fin rays, a bony tubercle on the lower jaw symphysis, absence of both a chin barbel and a ventral luminous organ, heavy pigmentation except on the caudal region and all fins, five first dorsal fin rays, 50-52 second dorsal fin rays, 45-50 anal fin rays, two to five pelvic fin rays, and 16-17 pectoral fin rays. The pelvic fins of specimens of 41.8 mm SL or less have five rays, whereas a single larger specimen of 46.2 mm SL has two rays. Ontogenetic reduction of pelvic fin rays in L. longipes thus evidently occurs at ca. 45 mm SL. In adults, vestiges of the three reduced inner fin rays are attached to the pelvic fin girdle along with the two elongated outer rays. The significance of the reduction of the inner pelvic fin rays in L. longipes is discussed, and some ecological features of the early life history of this species in the western North Pacific are noted.
