OBSERVATION ON PSOLUS SQUAMATUS (KOREN) FROM THE OKHOTSK SEA (DENDROCHIROTA : PSOLIDAE)

Abstract

Recently, the author had a chance of making some close observations on two specimens of Psolus collected from the Okhotsk Sea off the northeastern coast of Hokkaido Island, Japan. These specimens were easily identified with P. squamatus (Koren) on their general morphology. This is a well-known species found rather commonly in the seas of higher latitudes in both hemispheres. Therefore, little doubts remained about this identifications at first. However, the feature of ossicles seems to differ somewhat significantly between these two specimens, and these differences remind the author of two type of the species, mentioned in detail by Ekman (1923 and 1925). Moreover, some features of ossicles in the present specimens seem to be out of the trends supposed by previous researchers on this species. Thus, it seems to the author that the present only two specimens might give a clue to make clear the morphological range of this species, and this has made the author repeat the morphological descriptions of the specimens, in the present paper, but always keeping the two types of the species and the morphological trends so far proposed by previous researchers in his mind. Prior to enter the description, the author wishes to express his hearty thanks to Mr. Goro Osagawa for his generosity in submitting the specimens to the author's examination and to the Seto Marine Biological Laboratory for every facility in carrying on his studies. Further, the author's gratitudes are due to Dr. Takasi Tokioka for his kindness in reading the manuscript.