This species was first reported by ISHII (1916) under the name of Filaria cyprini. Molphological studies were made on 16 mature female nematodes gathered form the subcutaneous tissue of two year old carp, Cyprinus carpio, in Shimane prefecture in April and May, 1970, and led to the following conclusion. This species should be combined with Philometroides based on the RASHEED opinion (1963) in respect of its cuticular condition and should be, morphologically and ecologically, separated from the other species of the genus Philometroides: P. anguillae (ISHII, 1916), P. maplestonei (TRAVASSOS, ARTIGAS and PEREIRA, 1929), P. masu (FUJITA, 1940), P. plectroplites (JOHNSTON and MAWSON, 1940), P. sanguinea (Run., 1819) and P. seriolae (ISHII, 1931), and some closly related species bearing cuticular bosses on the surface of body; that is Philometra carassii (ISHII, 1931) and P. nodulosa THOMAS, 1929. Description: Body slender and almost uniformly broad except at extremities, 9.012.2 cm long, 0.62.0.90 mm broad; cuticle with numerous minute, irregularly distributed lobelike structures. Head bluntly rounded with four cuticular thicknings, but without any cephalic papillae. Mouth triangular formed with three anterior swellings of esophagus (0.0760.082 mm broad); esophagus, 2.89 3.32 mm long, 0.026 0.039 mm broad, with greatly developed esophageal gland, 0.16 0.21 mm maximum broad, which beginning at about level of nerve ring, 0.210.26 mm from head end. Intestine, about 0.29mm broad, gradually tapered and finally become a solid cord attached to body wall at tail and. Uterus voluminous, occupding most of body cavity; a pair of ovary short and uncoiled, 0.3960 mm Iong, 0.100.18 mm broad. Vulva and anus atrophied. Tail bluntly pointed with two or three cuticular thicknings, or without any shield.
A large number of encapsuled, philometrid nematodes were obtained from the fin and operculum of a right-eyed flounder, Limanda yokohamae, which was collected in Otsuchi Bay, Iwate Prefecture, in August, 1966. The present specimens closely resemble Philometpra mariae LAYMAN;this species was detected from the fin of Protopsetta herzensteini and Limanda sehrenki and the ovary of Sebastodes schlegelii in Peter the Great Bay. LAYMAN's description and figures are not detailed, and the present specimens are generally larger than LAYMAN's ones (Table 1). In philometrid nematodes, however, the size of the same species varies so much that the size is of little classificatory importance. The two worms were collected from the fin of the same pleuronectid fishes in the neighboring seas. Consequently, the present specimens are considered to belong to Philometra mariae. On the other hand, this species also resembles Clavinema parasiluri YAMAGUTI, 1935, which was obtained from the operculum and submaxilla of the catfish, Parasilurus asolus, in Lake Ogura, Kyoto. RASHEED(1963) revised the genus Philometra and asserted the invalidity of the genus Clavinema;main reason was the immaturing of C.parasiluri. Classificatory discussion is postponed to another occasion, however, it is conceived that the genus Clavinema is valid and Philometra mariae is transferred to the genus Clavinema.