during the postembryonic period. This can scarcely be a pure coinci- 

 dence. In conclusion one must say that the system of the Ancyrocephalinae 

 as a whole demands a rather substantial and careful revision, and that the 

 first priority should be given to the study of the species, which are so far 

 classified by us in the genus Ancyrocephalus. 



5. The development of Protancyrocephalus Bychowsky 



During our work on South Sakhalin in 1946 and on the Island of 

 Shikotan in 1949^ we studied the development of a new species and genus of 

 Ancyrocephalinae — Protancyrocephalus strelkowi Bychowsky parasitizing 

 the gills of young flounders, Lemanda aspera (Pallas). The absence of 

 connecting plates between the two pairs of middle hooks appears to be a 

 characteristic trait (of this species, nobis). The basic traits of organi- 

 zation are clear from the drawing of the adult form. 



The development of Pr. strelkowi from the moment of egg- 

 deposition to the emergence of the free -swimming larva takes place 

 during 8 to H days at average temperatures of 18° to 20°. The free- 

 swimming larva of this type has a length of 0. 08 - 0. 10 mm, it has a 

 relatively blunt anterior end and an elongated and sharpened posterior 

 end (Fig. 165). The ciliary covering is distributed just as it is annong 

 the larvae of Dactylogyrus, but both anterior groups do not merge at 

 their anterior ends, whereas the third group consists of tw^o clearly 

 divided sections of ciliary epithelium lying along the sides of a special 

 cone which is more sharply expressed than in Dactylogyrus and falls off 

 at the same time as the ciliary epithelium. The attaching disc js already 

 delineated from the body at the time of emergence of the larva from the 

 egg, but the 14 edge hooks have not yet cut through at this time and lie 

 with their points oriented toward the center of the disc. Their length is 

 about 0. 015 mm with terminal little hooks about 0. 005 mm. There are two 

 groups of head glands and four well-developed pigmented eyes in the 

 free -swimming larva just as in the adult aninaal. The digestive system 

 is of the customary type with a large pharynx and circular intestine. The 

 nervous system is almost invisible with the exception of the more 

 noticeable heau ganglia located at the level of the eyes. The excretory system 

 is unnoticeable. The development of edge hooks takes place as usual, p. 159 



their growth is insignificant because among fully matured egg -laying indi- 

 viduals the edge hooks have a length of not more than 0. 018 - 0. 020 mm. 

 The larvae which have just settled on the gills have 4 large transparent 



1 



We observed the settling of the larva on the gills during the entire time 

 of study (July-September): however, in the Bay of Anam on the Island of 

 Shikotan this process was of more concentrated nature (occurring, nobis) 

 at the end of July --beginning of August. In our diary it is noted that the 



170 



