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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Hydrophrya

Hydrophrya Nozawa, 1938 (ref. ID; 3475 original paper)
  1. Hydrophrya miyashitai Nozawa, 1928 (ref. ID; 3475 original paper)

Hydrophrya miyashitai Nozawa, 1928 (ref. ID; 3475 original paper)

Descriptions

The body appears like a hydranth; it is widest at the anterior end, and tapers slightly to the posterior end. The anterior end is evenly convex and surrounded by many tentacles arranged like a crown. The tentacles are thickest at the base and taper to the distal end where they are truncated abruptly. Thus the tentacles resembles closely those of Dendrocometidae and Ophryodendridae (especially Dendrosomides tumides Gajewskaja and Rhabdophrya trimorpha Collin) in their general features. The pellicle is thick, transparent, and covers the entire body and extends even to the tentacles which are not retractile. A bit of hyaline ectoplasm is protruded from the truncated end of tentacles as in the case of the forms belonging to Dendrocometidae. The number of tentacles increases with the growth of the animalcule: there are 10 to 20 tentacles in young, and 50 to 60 in adult individuals. At the posterior end of the body occurs a rudimentary test, which is thin, transparent, obliquely truncated and serves for the attachment of the animalcule. Both the body and the test are bilaterally symmetrical to the plane including the substratum to which the animalcule is attached. The macronucleus is band-shaped, never branched, and elongated along the longitudinal axis of the body. The contractile vacuoles are 8 to 12 in number, and are distributed evenly in the body. The present new species produces a kind of vermiform embryo. This characteristic places the new genus in Ophrydendridae. However, so far as my observation goes, the mode of formation of the vermiform embryo in the present species differs from any other type known in the Suctoria. First, the animalcule begins to divide longitudinally at the anterior end of the body, without any change in the tentacles. Consequently there is formed a monstrous animalcule with two tentacle-bearing heads and a single trunk. As the division proceeds farther, one daughter individuals which is to become the vermiform embryo, becomes longer and more slender than the other individual which remains as the mother animalcule. In the stage in which the fission plane attains close to the border of the test, the tentacles of the daughter individual are gradually absorbed, so that the latter individual assumes the appearance of a typical vermiform embryo. Then the latter is separated from the mother individual. Thus the formation of the vermiform embryo may be regarded as a kind of longitudinal fission accompanied by absorption of tentacles. The vermiform embryo which has become independent, creeps on the substratum by bending is body and adhering to the substratum by means of its anterior and posterior ends in an alternate manner very much like a leech in locomotion. When the embryo gets some suitable footing, it fixes itself to it with the posterior end and secretes a rudimentary test around it. The body thickens and shortens again, and the pellicle at the anterior end of the body differentiates into tentacles, thus the embryo acquiring the features typical of an adult Hydrophrya gradually. The nuclear changes which take place in the division remain still obscure in many points; but as for the macronucleus, the division seems to be performed partly by the longitudinal split and partly by the external budding. The vermiform embryo is much elongate and slender; the macronucleus is band-shaped and never branched the contractile vacuoles are multiple and arranged longitudinally. The ciliated embryo has not been observed, but seems to be present as in other genera of Ophryodendridae. (ref. ID; 3475)

Comments

The reproduction by means of the vermiform embryo has been known in Dendrosomides and Rhabdophrya, as well as in Ophryodendron. The former two genera have been classified into Dendrosomidae by Collin (1912-13), mainly on the basis of their morphological features. Moreover, these genera are distinct from the other genera of the same family in having a rudimentary stalk and in the formation of the vermiform embryo. Collin himself is of opinion that they may be the intermediate forms between Dendrosomidae and Ophryodendridae (Collin, 1912-13, p.379). Recently, Kahl (1934) has classified all the forms that multiply by means of the vermiform embryo into Ophryodendridae, so that the family comprises 4 genera: Collinophrya, Dendrosomides, Ophryodendron and Rhabdophrya. As he puts emphasis on the mode of reproduction more than on morphological characters, the distinctive features of Ophryodendridae have been reduced to two, namely, the production of the vermiform embryo and the longitudinal monaxiality of the body. This classification of Kahl needs some consideration, but for the present it seems best to place Hydrophrya in Ophryodendridae. (ref. ID; 3475)

Etymology

This animalcule seems to have been observed by Mr. Y. Miyashita (1933) who has proposed the generic name of "Hydranthosoma". This name, however, can not claim a priority right, because no specific name accompanies it. Here I propose "Hydrophrya" in place of Hydranthosoma, because the name seems to be more appropriate, while the specific name is dedicated to the discoverer. (ref. ID; 3475)

Type locality

Attached to the antennae of Xiphocaridina, a common fresh-water shrimp, found in a pond in Husimi (Rokuzizo), Kyoto (May 1937), Mizoro Pond, Kyoto (July 1937), and also in Lake Biwa. It occurs probably all the year round. (ref. ID; 3475)

Measurements

Length of body 150-200, breadth of body 30-40; length of vermiform embryo 200-250, its breadth 20-30 um. (ref. ID; 3475)